Download initial LIGO construction

LIGO M030023-00M
Project Description
Advanced LIGO: Context and Overview
Advanced LIGO
Gravitational waves offer a remarkable opportunity to see the universe from a new perspective,
providing access to astrophysical insights that are available in no other way. The initial LIGO
gravitational wave detectors have started observations, and are already yielding data that are
being interpreted to establish new upper limits on gravitational-wave flux.
The sensitivity of the initial LIGO instruments is such that it is perfectly possible that discoveries
will be made. If they succeed, there will be a strong demand from the community to improve the
sensitivity allowing more astrophysical information to be recovered from the signals. If no
discovery is made, there will be no lesser urgency to improve the sensitivity of the instrument to
the point where there is a general consensus that gravitational waves will be detected often and
with a good signal-to-noise ratio. The development of the next generation of instrument must be
pursued aggressively to make the transition from the initial to the Advanced detector in a timely
way – after the complete science run of the initial detector, but as quickly as possible thereafter.
The Advanced LIGO detector upgrade meets these requirements for an instrument that will
establish gravitational-wave astronomy. It is more than ten times more sensitive, and over a much
broader frequency band, than initial LIGO. It can see a volume of space more than a thousand
times greater than initial LIGO, and extends the range of compact masses that can be observed
at a fixed signal strength by a factor of four or more.
This proposal to build Advanced LIGO has grown out of the LIGO Scientific Collaboration and has
broad support both nationally and internationally from that community. A closely coordinated
community R&D program, exploring the instrument science and building and testing prototype
subsystem elements, has brought the design to a highly refined state. The LIGO Laboratory will
lead and coordinate the fabrication and construction of the instruments, with the continued strong
participation of the community.
Advanced LIGO can lead the gravitational-wave field to maturity.
The LIGO Mission
From its outset, LIGO has been approved by the National Science Foundation to directly observe
gravitational waves from cosmic sources, and to open the field of gravitational wave astronomy.
The program and mission of the LIGO Laboratory is to:






observe gravitational wave sources,
develop advanced detectors that approach and exploit the facility limits on interferometer
performance,
operate the LIGO facilities to support the national and international scientific community,
provide data archiving for the LIGO data and contribute computational resources for the
analysis of data,
develop the software infrastructure for data analysis and participate in the search and
analysis,
and support scientific education and public outreach related to gravitational wave
astronomy.
1
LIGO M030023-00M
LIGO is envisioned as a new capability contained in a set of facilities and not as a single
experiment. The LIGO construction project has provided the facilities that support the scientific
instrumentation, and the initial set of laser interferometers to be used in the first LIGO scientific
observation periods.
The facilities include the buildings and vacuum systems at the two observatory sites. The two
observatories are located at Hanford, Washington and Livingston, Louisiana. The performance
requirements on the LIGO facilities were intended to accommodate the initial interferometers and
future interferometer upgrades and replacements, and possible additional interferometers with
complementary capabilities. The requirements on the LIGO facilities were intended to permit
future interferometers to reach levels of sensitivity approaching the ultimate limits of groundbased interferometers, limited by reasonable practical constraints on a large facility at a specific
site.
This proposal is for the second generation of instruments to be installed in the LIGO
infrastructure, and is expected to bring the science of gravitational radiation from a discovery
mode to a mode of astrophysical observation.
LIGO Detector Scientific Goals
The scientific program for LIGO is both to test relativistic gravitation and to open the field of
gravitational wave astrophysics. More precise tests of General Relativity (and competing theories)
will be made. LIGO will enable the establishment of a brand new field of astronomy, using a
completely new information carrier: the gravitational field.
Initial LIGO represents an advance over all previous searches of two or three orders of
magnitude in sensitivity and in bandwidth. Its reach is such that, for the first time, foreseeable
signals due to neutron-star binary “inspirals” from the Virgo Cluster (15 Mpc distant) would be
detectable. At this level of sensitivity, it is plausible, though not certain, that the first observations
of gravitational waves will be made. If signals are not observed with initial LIGO, we will have set
challenging upper limits on gravitational wave flux, far beyond the capability of any previously
existing technology.
The Advanced LIGO interferometers proposed here promise an improvement over initial LIGO in
the limiting sensitivity by more than a factor of 10 over the entire initial LIGO frequency band. It
also increases the bandwidth of the instrument to lower frequencies (from ~40 Hz to ~10 Hz) and
allows high-frequency operation due to its tunability. This translates into an enhanced physics
reach that during its first several hours of operation will exceed the integrated
observations of the 1 year LIGO Science Run. These improvements will enable the next
generation of interferometers to study sources not accessible to initial LIGO, and to extract
detailed astrophysical information. For example, the Advanced LIGO detectors will be able to see
inspiraling binaries made up of two 1.4 MO• neutron stars to a distance of 300 Mpc, some 15x
further than the initial LIGO, and giving an event rate some 3000x greater. Neutron star – black
hole (BH) binaries will be visible to 650 Mpc; and coalescing BH+BH systems will be visible to
cosmological distance, to z=0.4.
The existence of gravitational waves is a crucial prediction of the General Theory of Relativity, so
far unverified by direct observation. Although the existence of gravitational radiation is not a
unique property of General Relativity, that theory makes a number of unambiguous predictions
about the character of gravitational radiation. These can be verified by observations with LIGO.
These include probes of strong-field gravity associated with black holes, high-order postNewtonian effects in inspiraling binaries, the spin character of the radiation field, and the wave
propagation speed.
2
LIGO M030023-00M
The gravitational wave “sky” is entirely unexplored. Since many prospective gravitational wave
sources have no corresponding electromagnetic signature (e.g., black hole interactions), there
are good reasons to believe that the gravitational-wave sky will be substantially different from the
electromagnetic one. Mapping the gravitational-wave sky will provide an understanding of the
universe in a way that electromagnetic observations cannot. As a new field of astrophysics it is
quite likely that gravitational wave observations will uncover new classes of sources not
anticipated in our current thinking.
Detector Design Fundamentals
The effect of a propagating gravitational wave is to deform space in a quadrupolar form. The
effect alternately elongates space in one direction while compressing space in an orthogonal
direction and vice versa, with the frequency of the gravitational wave. A Michelson interferometer
operating between freely suspended masses is ideally suited to detect these antisymmetric
distortions of space induced by the gravitational waves; the strains are converted into changes in
light intensity and consequently to electrical signals via photodetectors.
Limitations to the sensitivity come from two sources: extraneous forces on the test masses, and a
limited ability to sense the response of the masses to the gravitational wave strain. The thermally
excited motion of the test mass and the suspension is a fundamental limitation, intrinsic to the
way in which the measurement is performed; this influence is managed through the selection of
low-mechanical-loss materials and designs which capitalize on them. Seismic motion causes
forces on the mirrors due to the direct coupling through the isolation and suspension system, a
technical noise source which is minimized through design; and due to the time-varying mass
distribution near the mass (the Newtonian background).
Sensing limitations arise most fundamentally due to the statistical nature of the laser light used in
the interferometry, and the momentum transferred to the test masses by the photons (linking the
sensing and stochastic noise limitations to sensitivity). Technical noise sources that limit the
ability to sense include frequency noise and intensity fluctuations in the laser light. Scattered light,
which adds random phase fluctuations to the light, can also mask gravitational signals.
In the limit, valid for LIGO, that the instrument is short compared with the gravitational
wavelength, longer arms give larger signals. In contrast, most competing noise sources remain
constant with length; this motivates the 4km baseline of the Observatories. More generally, the
scientific capability of LIGO is defined within the limits imposed by the physical settings of the
interferometers and by the facility design, by the design of the initial detectors and ultimately by
future interferometers designed to progressively exploit the facility capabilities.
Although the rates for gravitational wave sources have large uncertainty, an improvement in
strain sensitivity linearly improves the distance searched for detectable sources. This increases
the detection rate by the cube of the sensitivity improvement.
The Observatories
LIGO Facility Scientific Capability
The LIGO facility design envisaged a progression of increasingly sensitive interferometers
capable of extending the physics reach of the observatories. In the design of the observatories,
LIGO incorporated critical design features into its facilities in order to optimize LIGO’s ultimate
performance capabilities. These features include a building foundation and infrastructure which
provides a clean, quiet environment for the instruments; a 4km long “L” ultra-high vacuum beam
tube system that brings scattered light and index fluctuations due to residual gas to a negligible
level; and a system of large vacuum chambers and pumping subsystems capable of providing a
flexible envelope for a wide range of detector designs, and delivering a vacuum quality that
3
LIGO M030023-00M
complements the beam tube subsystem. Advanced LIGO requires no changes in this
infrastructure to meet its scientific goals.
The LIGO Observatories
LIGO Hanford Observatory (LHO), located on the U.S. Department of Energy Hanford site in
eastern Washington, comprises 5 major experimental halls for the interferometer spread over 5
miles. 1.2-m diameter ultrahigh vacuum tubing connects these halls. Three support buildings
house laboratories, offices, and an amphitheater, and two additional buildings are associated with
maintenance and operations. Approximately 90,000 square feet of this space is under tight
environmental control to minimize contamination of sensitive equipment. The physical plant has
been designed to provide a low vibration environment similar to the surrounding undeveloped
shrub-steppe environment.
LHO houses two interferometers with arm lengths of 4 km and 2 km. The 4-km equipment is
installed in vacuum chambers in the corner station and the two end stations on each arm. The 2km equipment uses vacuum chambers in the corner station and the two mid-stations situated
halfway down each arm. The two interferometers share 2 km of beam tube along each arm. The
beam tube can eventually accommodate up to 5 interferometer beams and the current station
buildings can accommodate up to 3 interferometers to accommodate future growth.
Figure 1 LIGO Hanford Observatory (LHO) in aerial view. The 4-km interferometer
arms are shown with the 5 main buildings shown along the orthogonal arm layout.
4
LIGO M030023-00M
Figure 2 LIGO Livingston Observatory (LLO) corner region in aerial view.
The LIGO Livingston Observatory, located in pine forests between Baton Rouge and New
Orleans, Louisiana, is the site of a single 4-km laser interferometer gravitational wave detector.
Construction of its physical facilities, scaled to accommodate one interferometer, is complete. The
beam tube dimensions are identical to those at LHO.
Initial LIGO
Status of the LIGO Construction Project
The NSF Cooperative Agreement of May 1992 initiated LIGO Construction and Construction
Related Research and Development. The Project schedule and cost estimates were reviewed by
the NSF during September 1994 and presented to the National Science Board in November
1994. The total funding established by the Board for Construction and Construction Related R&D
were $272.1 million and $20.0 million, respectively. In addition, the NSF provided $68.7 million for
Operations through September 30, 2001 covering the period of Installation and Commissioning.
The LIGO construction effort is effectively complete, on cost and close to schedule.
Initial LIGO Detector Commissioning
Installation is complete for the three interferometers. The commissioning of the instruments
continues, with most subsystems completely operational and in use in the first science runs.
Several subsystems are coming on-line in preparation for the next science run. The instruments
have shown a steady improvement in sensitivity, at all frequencies in the planned observation
band, during the commissioning process. An example of progress is seen in Figure 3. All of the
instruments have made very significant progress toward the requirements proposed for initial
LIGO through a process of identification, tuning, and incremental changes in the detector
hardware as needed. The present limits to performance are understood through a combination of
5
LIGO M030023-00M
measurement and system modeling, and measures to bring the contributors to an acceptable
level are underway or in preparation.
Figure 3 This figure shows the progression in the strain sensitivity as a function of
frequency for the Hanford 4-km interferometer over the year from December 2001 to
December 2002. The most recent noise level is a factor 20 above the final specification
over a broad frequency range; many of the sources of excess noise have been identified
and are being addressed.
Future improvements to reach the design sensitivity will involve some modifications to the
electronics and to the mechanical infrastructure, and optimization of control systems and filters.
Substitute recycling mirrors (with an optimized radius of curvature for the observed mirror optical
properties) will be installed during favorable opportunities. It is anticipated that this series of
improvements in performance will largely take place between the upcoming second science run,
and the third science run, planned for the Fall of 2003.
The LIGO Science Runs
The observatories are now interleaving continued commissioning with science runs. The timing of
the runs is designed to balance the competing demands for improvements to the performance of
the machines (in sensitivity and duty cycle) with the need to observe.
6
LIGO M030023-00M
The first science run, S1, took place from 23 August through 8 September 2002, and involved the
three LIGO interferometers, the UK-German GEO-600 interferometer, with some overlap in
observing with the Japanese TAMA detector. The LIGO instruments operated in their design
configuration, and accumulated roughly 100 hours of observation in triple coincidence between
the two sites during the S1 run. LIGO Scientific Collaboration (LSC, please see below) “upper
limit” groups are undertaking the search for chirp signals from binary inspirals, periodic signals
from neutron stars, burst signals from e.g., supernovae and gamma ray bursts, and from a
possible stochastic noise background. The data analysis pipelines utilize a variety of
sophisticated filtering techniques – templates, time-frequency analysis, inter-interferometer
correlations, and use of the auxiliary and environmental data channels, as examples. Data are
also being correlated with relevant optical data and, in the case of supernovae, with neutrino
signals. Results from the analysis of S1 data, providing new upper limits to the gravitational wave
flux, are being prepared for publication.
The second science run, S2, is planned to take place from 14 February 2003 until 14 April 2003.
The objective for this run is to improve the upper limits on gravitational wave flux by at least an
order of magnitude compared to the S1 run. The present sensitivity of the instruments (January
2003) enables this goal. The third science run, S3, is planned for late 2003, following a significant
commissioning interval, and will represent a transition to a mode where observation dominates
over commissioning at the Observatories. We plan to intersperse science runs with periods
dedicated to detector improvements that will be coordinated with the LSC. The overall goal is to
obtain at least one year of integrated data with an RMS strain sensitivity of h ~ 10-21 (integrated
noise level in a 1 kHz band) within the first three years of observation (ending in 2006). Once that
goal is achieved and the physics results have been obtained, installation of improved
interferometers can commence.
LIGO Scientific Collaboration
A fundamental goal of LIGO has been to become a true national facility available to the scientific
community. In order to accomplish this, LIGO has broadened the participation to include the
community of scientists interested in participating in the LIGO research program by creating the
LIGO Scientific Collaboration (LSC)1. There are now some 470 members, from 38 institutions in
both the US and internationally. The LSC consists of both LIGO Laboratory scientists and those
from collaborating groups. The LSC is organized so as to provide “equal scientific opportunity” to
all members whether they are from within LIGO Laboratory or the broader LSC. It is growing
steadily and will remain open to new members over the coming years. It is worth noting that the
LSC has significant international participation, including collaborating groups from India, Russia,
Germany, U.K, Japan and Australia. The international partners are involved in all aspects of the
LIGO research program.
The full LSC collaboration meets twice yearly in an extended meeting, and various working
groups meet more frequently. The LSC has produced White Papers that outline the plans for
technical development of LIGO and for science data analysis. A publication policy and a
conference committee are active, as well as the other functions necessary to make it a ‘full
service’ organization.
The Advanced LIGO design, both in basic conception and in the detailed R&D, is very much a
product of the LSC (with a strong LIGO Laboratory element). The technical working groups have
been and continue to be central to the advancement of the design, and this proposal is made with
the strong support of the many participating institutions in the LSC.
In addition, LIGO has been organized such that the search for astrophysical signals and
interpretations will be performed through the LSC. The collaboration members committed to
1
http://www.ligo.org
7
LIGO M030023-00M
"LIGO I", the initial LIGO detector science runs, will be responsible for the science in this
beginning phase of observation. This group in LIGO is well defined and presently consists of 111
LIGO Laboratory scientists and 134 scientists from collaborating institutions.
Preparation tasks for the runs are organized within the LSC, LSC members participate in the data
taking runs, and the analysis of the data is coordinated through the LSC proposal driven process.
LIGO is available to all interested researchers through participation in the LSC, an open
organization. To join, a research group defines a research program with the LIGO Laboratory
through the creation of a Memorandum of Understanding (MOU) and relevant attachments 2. The
group then presents its program to the LSC. When the group is accepted into the LSC it becomes
a full scientific partner in LIGO.
Exploiting the LIGO Capability: Advanced LIGO
As noted above, LIGO is designed to evolve and to support improvements in gravitational wave
detectors. A natural time for an upgrade to the instruments can be foreseen once the initial LIGO
goal of one year of integrated observation has been met. The initial LIGO infrastructure is well
designed to deliver its planned performance, and small advances in sensitivity at higher
frequencies may be possible with e.g., modest increases in the input laser power. However, a
large improvement will require an upgrade of the entire detector in a coordinated fashion. The
considerable research and development in the Laboratory and the greater community that has
taken place since the initial LIGO interferometer design was frozen enables this improvement.
The Advanced LIGO instrument fulfills our requirements of a significant step forward in sensitivity,
and can be delivered on a time scale that meshes with the end of the Initial LIGO observation
plan.
Overview of Advanced LIGO
The sensitivity goals for the Advanced LIGO detector systems are chosen to enable the advance
from plausible detection to likely detection and rich observational studies of sources. These
sensitivity goals require an instrument limited only by fundamental noise sources over a very wide
frequency range. To achieve this sensitivity, almost every aspect of the interferometer must be
revised from the initial LIGO design. The system briefly described below is the reference concept
that is the basis for structuring the R&D program and the detailed studies of system tradeoffs
performed as R&D results define the feasible parameters. A more complete description of the
proposed detector, organized by subsystem, is found in the Advanced LIGO Project book,
starting on page 43 of this document.
The basic optical configuration is a power-recycled and signal-recycled Michelson interferometer
with Fabry-Perot “transducers” in the arms. Using the initial LIGO design as a point of departure,
this requires the addition of a signal-recycling mirror at the output “dark” port, and changes in the
RF modulation and control systems. This additional mirror allows the gravitational wave induced
sidebands to be stored or extracted (depending upon the state of “resonance” of the signal
recycling cavity), and leads to a tailoring of the interferometer response according to the
character of a source (or specific frequency in the case of a fixed-frequency source). The planned
upgrade includes the three LIGO interferometers, allowing e.g., one interferometer at Hanford
and the interferometer at Livingston to be tuned to be broadband, and the second interferometer
at Hanford to be used as a higher-frequency narrowband detector.
2
http://www.ligo.org/mou/mou.html
8
LIGO M030023-00M
To improve the quantum-limited sensitivity, the laser power is increased from the initial LIGO
value of 10 W to ~200 W. The conditioning of the laser light follows initial LIGO closely, with a
ring-cavity mode cleaner and reflective mode-matching telescope.
Whereas initial LIGO uses 25-cm, 11-kg, fused-silica test masses, the test mass optics for
Advanced LIGO are larger in diameter (~30 cm) to reduce thermal noise contributions and more
massive (~40 kg) to keep the radiation pressure noise to a level comparable to the suspension
thermal noise; sapphire is the baseline material for the test masses. Compensation of the thermal
lensing in the test mass optics (due to absorption in the substrate and coatings) is added to
handle the much-increased power – of the order of 1 MW in the arm cavities.
The test mass is suspended by fused silica fibers, in contrast to the steel wire sling suspensions
used in initial LIGO. The resulting suspension thermal noise is anticipated to be less than the
radiation pressure noise (in broad-band observation mode) and to be comparable to the
Newtonian background (“gravity gradient” noise) at 10 Hz. The complete suspension has four
pendulum stages, contributing to the seismic isolation and providing multiple points for actuation.
The seismic isolation system is built on the initial LIGO piers and support tubes but otherwise is a
complete replacement, required to bring the seismic cutoff frequency from 40 Hz (for initial LIGO)
to 10 Hz. RMS motions (frequencies less than 10 Hz) are reduced by active servo techniques.
The result is to render the seismic noise negligible at all observing frequencies. Through the
combination of the seismic isolation and suspension systems, the required control forces on the
test masses will be reduced by many orders of magnitude in comparison with initial LIGO,
reducing also the probability of non-Gaussian noise in the test mass.
The overall performance of Advanced LIGO is dominated at most frequencies by the quantum
noise of sensing the position of the test masses, with a contribution at mid-frequencies from the
internal thermal noise of the test masses. This design, with modest enhancements after it enters
scientific use, should take this interferometer architecture to its technical endpoint; it is as
sensitive as one can make an interferometer based on familiar technology: a Fabry-Perot
Michelson configuration with external optical readout using room temperature transmissive optics.
Further advances will come from R&D that is just beginning, such as the exploration of cryogenic
optics and suspensions, purely reflective optics, and a change in the readout to one which fully
exploits our nascent understanding of the quantum nature of the measurement (e.g., quantum
non-demolition speed meters). These later developments will be timely for instruments to be
developed in the second decade of this century.
Advanced LIGO R&D 2002-2006
During 2002 through 2006, most LIGO Laboratory detector R&D is being directed at the
challenges posed by the Advanced LIGO design. This R&D program is a significant part of the
larger R&D program of the LIGO Scientific Collaboration. The LSC program has been developed
in a collaborative manner and is coordinated through the LSC Working Groups and by the LIGO
Laboratory.
The R&D program currently underway, supported by the NSF under cooperative agreement PHY0107417, is designed to support this construction proposal. This proposal requests that
construction funding commence at a time when the major R&D issues are satisfactorily resolved,
and the subsystems are ready for fabrication.
The activities carried out prior to construction funding include small-scale fundamental research
motivated by Advanced LIGO. Examples of this are studies of core optic substrate absorption,
measurement of mechanical losses in suspension fibers, and studies of candidate photodetectors
for the gravitational wave readout. The R&D program also includes large-scale prototypes of
subsystems such as full-scale seismic isolation systems, full-scale suspensions, and full-scale
9
LIGO M030023-00M
core optics. In order to carry out this research, in most cases these components must be fully
engineered to the realistic requirements and configuration of Advanced LIGO. In order to study
the performance and control of a suspension subsystem, for example, the prototype studied must
represent the Advanced LIGO design down to details such as suspension fiber material, bonding
technique, as well as control electronics design, component selection, and physical layout. This
kind of rigorous full-scale development program is needed to reduce risks prior to defining and
committing to a construction project and to minimize the time between installation and the start of
observations at the design sensitivity.
Advanced LIGO Schedule and Cost
The Advanced LIGO fabrication and construction schedule grows out of the tightly coordinated
R&D program currently underway. The objectives in establishing the schedule are to
 Allow the initial LIGO instruments to be fully exploited, and in particular to ensure the
commitment to a full integrated year of observation with initial LIGO instruments.
 Allow a complete R&D cycle, with extensive testing of final designs, before committing to
fabrication.
 Bring the Advanced LIGO instruments on-line as quickly as possible to meet the
demands of the community for the observing capability of the Advanced LIGO detector.
The schedule is based on our extensive experience with the design, fabrication, construction, and
commissioning of the Initial LIGO detectors.
The highlights of the schedule are
 Receipt of funding for the fabrication and construction project in early 2005, with some
advance funding for critical long-lead items in early 2004.
 Delivery of first interferometer hardware to the observatory staging facilities in mid-2006.
 Decommissioning of initial LIGO at the LIGO Livingston Observatory in early 2007, and
simultaneous start of installation of Advanced LIGO there.
 Decommissioning of initial LIGO at the LIGO Hanford Observatory in late 2007, and
simultaneous start of installation of Advanced LIGO there.
 Both observatories in commissioning by mid-2008.
 Both observatories in operation by late 2009.
The cost estimate developed for this proposal was performed at the lowest feasible level, given
the present level of development in the WBS, in a bottom-up manner. Most subsystems have
been costed at a level of detail comparable to initial LIGO; several have not achieved the maturity
in R&D to allow this level of detail, but carry contingency appropriate to the basis. The techniques
used were the same methods used to estimate initial LIGO construction costs, though our cost
experience in initial LIGO substantially improved the input knowledge base for the new estimate.
Contingency was estimated using the formal graded approach to assessing technical, cost and
schedule risk that was used in initial LIGO.
The joint United Kingdom/German GEO Project3 has proposed to provide a capital investment in
this construction project. The UK proposal is for approximately $11.5 million. They propose to
apply these resources to providing the suspension subsystem, including suspension assemblies,
their controls, and installation and commissioning. The German proposal is for the design and
fabrication of the pre-stabilized laser subsystem, and the contribution is also planned to be valued
at $11.5 million. The GEO Project is a full partner in Advanced LIGO, participating at all levels in
the effort.
3
http://www.geo600.uni-hannover.de/
10
LIGO M030023-00M
A significant role in Advanced LIGO R&D, construction and implementation is also proposed by
the Australian Consortium for Interferometric Gravitational Astronomy4 (ACIGA). The Australian
proposal is for approximately $2.9 million, and will support part of the output mode filtering
system and R&D to develop a variable transmission signal-recycling mirror.
With the GEO and ACIGA capital contributions, and with funds already applied to Advanced LIGO
from funds awarded in the current LIGO Cooperative Agreement and continued in the presumed
successor agreement, this proposal requests $ XXXXX K in as-spent funds for Advanced LIGO
construction and early commissioning.
4
http://www.anu.edu.au/Physics/ACIGA/
11
LIGO M030023-00M
Results and Accomplishments from Prior Support
This section describes the state of the LIGO Laboratory at the close of 2002, summarizing the
status of the construction, commissioning, operations, data analysis, collaborative research and
support of the involved community, advanced detector R&D and efforts on education and
outreach designed to produce broader impacts of LIGO. Further details are available in the
references.
The narrative description of progress follows the task organization of the LIGO Laboratory in
2002.
Observatory Operations and Detector Commissioning
The Detector and Engineering Groups and the Observatory staff are focused on commissioning
and operating the interferometers. Emphasis is on reducing noise and improving duty cycle and
on refining the design and implementation of interferometer subsystems based on our growing
operational experience.
At the close of 2002 we had achieved strain sensitivity better than has been achieved with any
previous broadband detector for all three interferometers. This was the case over the entire
gravitational wave band from 100Hz to several kHz. These improvements contributed to a very
successful first Science Run (S1) and position us well for the S2 run in February, 2003.
Hanford and Livingston Observatories
The sensitivity of the interferometers continued to improve in 2002. This improvement resulted
from control subsystems being brought into operation, improvements in the performance of
electronics and software subsystems, and tuning of the controls system. The best noise
equivalent strain sensitivity (January 2003) is better than 710-22/Hz in the four-kilometer
interferometer (H1) and 2x10-21/Hz in the two-kilometer interferometer (H2), and 310-22/Hz I at
the Livingston four-kilometer interferometer.
Engineering runs 6, 7 and 8 were conducted to test the interferometers. During E7 the
interferometers were operated in coincidence between the two Observatories, with GEO-6003,
and with ALLEGRO5, the cryogenic resonant bar detector at Louisiana State University (LSU).
All interferometers participated in the first Science Run (S1) from August 23 to September 9,
2002, collecting nearly 100 hours of triple-coincidence data. GEO-600 and TAMA6 also scheduled
observing runs to coincide with S1.
At both Hanford and Livingston we completed the last phase of facilities construction, providing
laboratory, office and meeting space. We hired additional staff required as we approach twentyfour-hour-per-day, seven-day-a-week operation.
5
6
http://gravity.phys.lsu.edu
http://tamago.mtk.nao.ac.jp/
12
LIGO M030023-00M
Figure 4 Strain sensitivity improvement for the Livingston 4-Km interferometer during
2002.
Engineering Runs
The seventh engineering run started on December 28, 2001, and data collection was completed
January 15, 2002. The Livingston four-kilometer interferometer and the Hanford two-kilometer
interferometer had a combined duty cycle of about 40 percent. The overlap was primarily at night
when the seismic conditions at Livingston were relatively quiet (this operational limitation is being
addressed; see below). Combined observations with the bar detector at Louisiana State
University (LSU) began on Wednesday, January 9. Concurrently, GEO operated a powerrecycled Michelson interferometer.
We conducted an engineering run (E8) from June 8 to June 10, 2002 at the LIGO Hanford
Observatory. The objective was to evaluate the Data Monitoring Tool (DMT) software developed
by the LIGO Scientific Collaboration (LSC) in preparation for the first science run (S1). We tested
sixteen monitoring programs under real operating conditions. Useful recommendations for
needed modifications were provided to software authors. As a result, DMT programs ran reliably
and usefully during S1.
DMT is an elaborate and useful suite of programs that continuously review the interferometer
data streams, watch for various potential problems, and record summary information for later use
concerning the three interferometers and their environments. DMT also supports interactive
exploration of the data in the gravitational-wave channel and of non-linear noise processes. It
supplies the non-strain-channel 'vetoes' used to improve the statistics of the processed strain
data.
13
LIGO M030023-00M
Science Runs
We have planned an initial progression of three science runs, interleaving interferometer
development and improvement with increased scientific reach for each run. Important data
analysis, and interferometer commissioning and development work are implemented between the
scientific running periods. The three consecutive runs will provide a baseline for LIGO Data
Analysis System (LDAS) development, detector modeling and diagnosis, as well as
interferometer commissioning, modification, and revision. All three science runs are the joint
responsibility of the Laboratory and the LSC.
We completed a very successful first science run (S1), ending on September 9, 2002. Analysis of
the data from this run, and further interferometer commissioning and modification is under way.
Release of results for publication from the S1 analysis is planned for February 2003.
The S1 run included coincidence operation with the GEO3 600 interferometer and TAMA6 300
detector. This coincidence effort promises additional results and early experience running a
network of detectors across the globe.
The experience gained during S1, including complete upper-limit operation and orientation of the
LIGO-LSC scientific and operations staff, will help us to prepare for the second science run (S2),
which is scheduled to start in February 2003.
Further commissioning prior to S2 is nearing completion and there is a staged “freeze” to the
configuration of the three interferometers that will take place in late January 2003. The goal for S2
is at least an order of magnitude improvement in scientific reach, and we plan S2 to last
approximately 8 weeks. With the presently realized improvements in strain sensitivity and
duration, S2 will provide an opportunity to set very significant upper limits. We expect that S1 and
S2 data will provide new publishable limits on the broadband gravitational wave flux, well beyond
what has been previously reported.
Following S2 we plan additional commissioning including the important installation of the
Livingston seismic pre-isolation system. S3, scheduled for late 2003, will mark the beginning of
the first true search for gravitational waves with astrophysical significance.
Commissioning
At the close of the year we had achieved similar performance levels with all three instruments (H1
and H2 at Hanford, L1 at Livingston). We accomplished this by upgrading all hardware to the
same revision and sharing commissioning experience through close collaboration and personnel
exchanges between observatories.
The most significant changes were the installation of and completion of the commissioning of the
digital suspension controllers. This second version of the electronics for pointing and actuating
the test masses provides great flexibility in the design of (digital) filters to allow large actuation
forces outside of the gravity-wave band to counter seismic motion, but very low noise operation in
the target band. In addition, mechanical cross coupling in the suspensions can be 'inverted' to
decouple length and angle motions.
In a related effort, the optical levers were refined and tuned. The optical levers provide an
independent measure of optical alignment and are used to establish the initial alignment of the
instruments in preparation for locking (brought into the linear control regime). They can also be
used to maintain the alignment during operation for those degrees of freedom, in anticipation of
the completion of the wavefront sensor commissioning. The digital filtering capabilities of the
14
LIGO M030023-00M
suspension controllers improved the low-frequency performance of the optical levers and thus the
overall interferometer sensitivity.
In the length control system, experience indicated that a change in control topology could provide
a significant reduction in the appearance of frequency noise in the strain output. Once the
instrument is locked an automated script transfers actuation away from the test masses and to
the mode cleaner and laser systems. This also provided improvements in the low-frequency
regime.
The improvements in the controls allow us to increase the light intensity on the main sensing
photodiodes, reducing the photon shot noise at high frequencies. We moved from being
dominated by electronics noise to seeing the quantum noise, as anticipated by the interferometer
design.
At the Livingston Observatory, seismic noise in the 1-3Hz band arising from tree harvesting,
traffic, and other human activity in the area surrounding the site continues to limit the operation of
the interferometer to periods of low seismic noise, generally night time and weekends. Weatherinduced seismic noise in the 0.1-0.3 Hz band has also interfered with operation at times. In
response to these disturbances, several technical approaches have been initiated. We worked
together with our LSC collaborators at Louisiana State University (LSU), to incorporate the fine
actuators at the end test masses into a feedback loop to reduce the seismic motion of the stacks
between 1 and 10 Hz. These actuators remove the differential motion due to the tides and reduce
the microseism. Using four longitudinal actuators at the corners of the support beams and two
geophones as inertial sensors mounted on the beams, we reduced the Q's of the stack mode at
1.2 and 2.1 Hz by a factor of seven. These are the key modes for the excess test mass
excursions driven by seismic motion at Livingston. This near-term solution to reduce excess
seismic noise due to logging in the vicinity of the interferometer will be supplanted by the preisolator after S2 (see section Seismic Isolation Upgrade below.) In the interim, we can achieve
higher duty cycle and greater sensitivity.
Investigations of Radio-Frequency Interference (RFI) and Electromagnetic Interference (EMI) in
the detectors indicate that we have been suffering contamination from the switching-mode power
supplies used as well as cross-coupling from digital electronics to low-level analog electronics. By
modifying some power supplies (to linear models) and changing cabling and cabling configuration
we successfully reduced the RFI/EMI in the subsystems selected. We have developed a
comprehensive plan to address the contamination, which will be executed in stages starting after
the end of S2.
Seismic Isolation Upgrade
We are developing a pre-isolator to address the excess seismic noise at Livingston. The technical
solution is an early implementation of the external pre-isolator for Advanced LIGO. Our LSC
Stanford University collaborators transferred their basic conceptual design for the hydraulic
portion of the system to the LIGO-LSC collaboration for continued development. Prototypes for
both the Hydraulic External Pre-Isolation (HEPI) and Electro-Magnetic External Pre-Isolator
(MEPI) prototypes are complete and testing and control law development is underway. We plan
to complete the testing and to fabricate and install the pre-isolator at Livingston shortly after the
S2.
15
LIGO M030023-00M
Data and Computing Group
Simulation and Modeling
We improved the second generation LIGO simulation package based on the end-to-end (e2e)
time domain simulation engine to incorporate more realistic hardware and servo system models
with the latest detector designs. Notably important recent additions include the Wave Front
Sensor (WFS) and the Alignment Control System using WFS signals, and the common mode
servo. Our ability to simulate LIGO end-to-end is nearly complete.
Sample sensitivity curves simulated by the model and the LIGO sensitivity measured during S1
are shown in Figure 5.
Figure 5 Actual and simulated sensitivity noise for S1.
While additional adjustment of the input parameters of the simulation in Figure 5 is needed, the
good agreement demonstrates the relative completeness of this model. Note that the simulated
noise curve is calculated from simulated time-series data (ground noise, input photon shot noise,
electronics noise, etc.), enabling simulation ‘experiments’ of changes in e.g., the isolation system,
or control law tuning, without disturbing the actual interferometer.
We have improved the time domain simulation code to support the more demanding
functionalities of the simulation code. Recent improvements include a more accurate treatment of
the response of the Core Optics Component to the frequency noise and improvements of the
16
LIGO M030023-00M
Modal Model. Other improvements include an interface, which makes it possible to run the
simulation under different conditions, analogous to changing the hardware or software setup
during LIGO operation, without human intervention. These changes make it even easier for nonexpert to use and extract more useful information.
A new object-oriented field/optics model is being developed. The new scheme makes it possible
to easily implement realistic features like wedge angles or internal reflections in substrates.
Commissioning Modeling
Interferometer locking at the Livingston site is being compromised due to seismic noise induced
by passing trains and on-going logging activity near by. The effects of these seismic noise
sources on the interferometer performance are being modeled to support the required design
modifications in the seismic isolation system.
Now that the wave front sensing is fully implemented in the simulation, we have begun a
collaboration to understand the complex response of the real LIGO wave front sensing. We have
modified the simulation program interface to make it easier for the non-expert to use it and
analyze the response.
We investigated the effect of heating of the input test mass (ITM) after a long time in lock at a
high input power using the Han2k package (the first generation LIGO simulation model used for
the lock acquisition design). The study showed that the model could cover a satisfactorily wide
range of ITM deformation.
Near Term Plans
Now that the simulation package is almost completed, the focus will move to the application
simulation to assist in the noise reduction effort for all three interferometers. We are working
towards establishing an effective simulation effort at each LIGO site. Three major development
areas are planned: support of mirror imperfections, implementation of a refined field/optics model
in the e2e simulation engine framework, and speed improvements of the simulation code. Alfi5
development will continue. Although basic features have already been incorporated, further
refinements are needed to improve productivity.
LIGO Data Analysis System (LDAS)
LDAS Software Development
LDAS software development continued through 2002. Preparations for engineering run E7 and
the first science run (S1) drove our effort. We applied lessons learned during E7 to our current
LDAS release (0.5.0), which was used during S1. Intense use of LDAS during E7 and S1
enhanced our understanding of the user and usage modes. LDAS systems are now being used at
all Laboratory sites as well as at several LIGO Scientific Collaboration (LSC) Institutions
(University of Wisconsin at Milwaukee, Penn State University, University of Texas at Brownsville,
and Australian National University). LDAS 0.5.0 uses the new international standard (FRAME 6)
for frame data storage.
We used LDAS version 0.5.0 during S1, and subsequently for all upper limits analyses. We
achieved significant improvements in the system performance, grid safety, and memory
management. LDAS 0.5.0 is the first release to have the ability to manage raw data on the large
17
LIGO M030023-00M
RAID7 storage systems now on-line at Hanford and Livingston. This release performed reliably, to
the 99 percent level, on S1, up from the approximately 90 percent level for the release used
during E7. LDAS 0.5.0 also produces reduced frame data files, which are easier to share.
Experience with the more than 10 terabytes of data collected during E7 has underscored the fact
that we will need this capability for longer data runs.
We made significant improvements in the processing efficiency and enhanced the interface
protocol used by the search codes to support raw sequences in data exchanges. Thorough
testing and the sharing of pre-release frame files with the Virgo8 project (Italian-French laser
interferometer collaboration) have allowed us to significantly improve the reliability of the code,
and assure compliance with the specification.
The LIGO Scientific Collaboration (LSC) upper limits groups used LDAS online during the science
run S1, and nearly 230,000 jobs were submitted to the Hanford, Livingston, and MIT systems
during the run. This is roughly twice the number of jobs submitted during E7. These jobs inserted
over 7,000,000 rows into the databases. This represents roughly the same number of triggers
and events as were produced during E7 even though the burst group chose not to enter their
event candidates into the database during this run.
LIGO data collected during E7 and S1 was successfully transferred from the remote
observatories to the Caltech archive and from there, using secure mechanisms based on
GriPhyN9 (see “Grid Computing and Related Research” below) tools, to the LSC Tier 2 centers
where members of the LSC are conducting a significant proportion of the LIGO science.
LDAS Hardware
The primary activity was upgrading the Storage Area Network (SAN) and the compute clusters at
the Hanford and Livingston Observatories in preparation for the first science run (S1). The
production analysis system at Caltech is fully operational with all of the servers integrated with
Beowulf clusters. In addition to an initial 16-node Beowulf cluster, we installed a 17-terabyte-disk
farm holding all of the S1 data. All of the LDAS servers in five of the six LIGO Laboratory run
LDAS systems have been upgraded to Gigabit Ethernet networks. The Gigabit Ethernet network
was also replicated at the Observatories where it connects the main buildings housing data
acquisition equipment to the new facilities housing the LDAS equipment.
SunFire880 servers were integrated into the existing LDAS systems to operate as the main data
servers. The large disk storage systems at the observatories were moved to the new servers.
All engineering and science run data generated by the LIGO Laboratory have been archived at
Caltech in the LIGO data archive running HPSS10. The current archive11 contains 54 terabytes.
After a thorough review and with consultation from experts in the field, we decided to replace
HPSS platform with SAM-QFS12. The SAM-QFS archiving platform offers a number of important
enhancements relative to HPSS namely: simplicity, reliability, ability to move media between
systems without data replication, sufficiently low licensing fees to allow use at the Observatories
as well as Caltech, disaster recovery, metadata performance, and minimization of the number of
vendors supporting LDAS. Initial testing and disaster recovery experiments have gone well. A
7
RAID - Redundant Array of Independent Disks
http://www.virgo.infn.it/
9 GriPhyN: Grid Physics Network, the GriPhyN Project is developing Grid technologies for scientific
and engineering projects that must collect and analyze distributed, petabyte-scale datasets. GriPhyN
research will enable the development of Petascale Virtual Data Grids (PVDGs) using a Virtual Data
Toolkit (VDT). (http://www.griphyn.org/index.php)
10 The High Performance Storage SystemTM--IBM (HPSS); http://www4.clearlake.ibm.com/hpss/index.jsp
11 http://www.ldas-sw.ligo.caltech.edu/archive/hpss
12 SUN Storage and Archive Management system
8
18
LIGO M030023-00M
demonstration run during S1 verified SAM-QFS performance as well as its capability to archive
and retrieve the 17 terabytes of S1 data without corruption.
We are adding a grid interface currently installed at Caltech to the LIGO LDAS systems at
Hanford and Livingston Observatories, and at MIT. We are expanding the existing LIGO compute
clusters at Caltech, Hanford, Livingston, and MIT with additional nodes to establish sufficient
processing capability for scientific analysis. A procurement of up to1000 central processing units
is anticipated during the first half of the next fiscal year. A trade study is currently under way to
choose between the currently used Intel hardware and newer technology that offers significant
cost or performance advantages.
We are also planning to expand our data storage capability at all LIGO sites. We have been
evaluating the feasibility of using Large Disc Storage IDE technology for non-critical path
components. The IDE tape storage alternative is a factor of 10 less expensive than the
comparable SCSI product. IDE disc technology, though less expensive, might even surpass SCSI
disc storage capability. We have purchased 10 terabytes of IDE disc storage to support a
technology demonstration.
Grid Computing and Related Research
LIGO is making strides towards performing scientifically significant data analysis using Grid
resources. As part of the collaboration this past year between the LIGO and the GriPhyN9
projects, we have focused on a specific LIGO problem: the gravitational-wave periodic source
(“GW pulsar”) search. The data needed to conduct the search spans a significant period of time
(~4 months, 2×1011 points). A source would appear on the frequency-time image as a wavering
line, whose frequency might be 1 kHz, but modulated by a few parts in 106 over a day and a few
parts in 104 over a year. In addition, if the source exhibits any secular variations due to slowing
down of its rotational period, these will be encoded in the data as well. We successfully ran more
than 50 pulsar searches, collecting useful statistics on the performance of the system for future
improvements13.
We have successfully integrated LIGO's existing data analysis with a Grid environment interface.
The LIGO Data Analysis System (LDAS) can perform a wide range of sophisticated and
computationally intensive data analysis. We are developing an infrastructure in which LDAS can
be accessed as a Grid resource and to also enable LDAS to schedule its jobs on the Grid.
General Computing
We have completed and implemented the General Computing Policy. An accompanying
computing and IT security plan was also developed and adopted. A baseline security audit was
conducted at all four LIGO sites. A number of issues were discovered and addressed.
We are developing a schedule for additional audits during FY 2003. Security and related services
have a high priority. Additional network security hardware will be installed at all locations.
We converted the Hanford Observatory network connection to the DOE ESnet through PNNL 14
from a T1 line to 10 Megabit Ethernet-over-fiber. This required purchasing and installing media
converters at both ends of the connection, PNNL and Hanford. We are preparing to move from
the Ethernet network to an OC3 network connection through ESnet. This upgrade is scheduled to
take place during the first half of FY 2003.
A new web server was added that is devoted exclusively to LIGO Scientific Collaboration (LSC)
web sites. We acquired the domain name, ligo.org, for this server through a charitable gift.
13
14
The statistics are summarized at http://smarty.isi.edu:8680/cgi-bin/final.pl
Pacific Northwest National Laboratory
19
LIGO M030023-00M
Campus Research Facilities
40-Meter Laboratory
LIGO operates a 40-Meter prototype gravitational-wave interferometer on the Caltech campus. To
prototype the Advanced LIGO optical configuration and controls, and study its performance, a
fully instrumented suspended-mass interferometer is needed. The 40-Meter facility is dedicated to
this task.
A Conceptual Design Review for the 40-Meter Dual Recycling project was held in October 2001.
At that time, detailed conceptual designs were presented (with accompanying documentation) for
the overall project, the tentative optical configuration and control scheme, the optical layout, all
sensing table instrumentation, core suspended optics, mechanical suspensions, digital
suspension controllers, and auxiliary optics (stray light control, initial alignment system, optical
levers, video monitoring, etc), laboratory infrastructure and vacuum systems, environmental
monitoring, data acquisition, computing and networking.
As of January 2003, we are on schedule. In particular, the following components and subsystems
are implemented:







The infrastructure has been brought to specifications. The laboratory building has been
expanded and upgraded, all electronics racks needed for the full interferometer controls
have been installed, and all optical tables and optical enclosures have been installed.
Vacuum equipment (pumps, gauges, RGAs) have been upgraded.
The existing vacuum envelope has been augmented with a new output optic chamber
with seismic stack, a 13-meter mode cleaner beam tube, a small chamber and seismic
stack for the end mode cleaner suspended optic.
A commercial active seismic pre-isolation system (STACIS) was installed on all four test
mass chambers and is now in continuous use.
An Initial-LIGO pre-stabilized laser (PSL) was installed in spring 2001. It has been fully
commissioned and characterized, and is in continual use.
The optics and suspensions for the 13-meter mode cleaner were produced, and in April
2002, the three suspended optics for the mode cleaner were hung, tested, and installed
into the vacuum envelope.
The characterization of the mode cleaner performance, and its interaction with the prestabilized laser system, occupied much of fall 2002. By the end of December 2002, the
noise performance of the system met specifications.
All of the core optics and suspensions for the main dual recycled interferometer (including
spares) were produced August 2002. Three core optics (the beamsplitter, ITMx, and
ITMy) were suspended and damped in September 2002.
Thus, there has been considerable progress in the fabrication and commissioning of a full dualrecycled interferometer with LIGO-engineered controls. To complete the fabrication phase, the
remaining optics and suspensions must be installed, and some additional sensing and control
electronics must be designed and fabricated. These systems will be installed, and the process of
commissioning them begun, by summer 2003. First experiments in dual recycled configuration
response, lock acquisition, and control are planned for 3Q 2003, and are expected to take at least
a year. We expect that LSC members, as well as students, will participate in this most interesting
phase of the project.
20
LIGO M030023-00M
MIT Facilities (LASTI)
The LIGO Advanced System Test Interferometer (LASTI) facility is designed to develop and test
advanced and improved LIGO subsystems at full mechanical scale, without disrupting or delaying
scientific operations at the observatory sites. Located in a purpose-built high bay laboratory on
MIT's northwest campus, LASTI comprises a suite of vacuum chambers and beam tubes (on a
much-reduced 16m baseline), seismic isolation supports, lasers, and electronic and computing
infrastructure closely replicating those found at the Livingston and Hanford LIGO observatories.
Figure 6 The LASTI vacuum envelope. The system consists of three ‘HAM’ auxiliary
optics chambers, one ‘BSC’ test mass chamber, connecting tube, and pumping system.
The photo is looking along one arm, and was taken before the seismic isolation support
piers and clean rooms were installed.
During fiscal 2002, LASTI was primarily dedicated to accelerated development of seismic preisolators for the Livingston Observatory, which has been impacted by excess environmental noise
due to nearby human activity. Prior to discovery of this phenomenon, LASTI had been slated to
next receive prototypes of the fully active seismic isolation systems planned for Advanced LIGO.
To accommodate testing the initial LIGO pre-isolator retrofit, we instead rapidly installed an initial
LIGO isolation stack into our BSC (Basic Symmetric Chamber) early in the year. Another
chamber, one of our three HAM (Horizontal Axis Modules), already carried an initial LIGO
isolation stack used in prior work commissioning our laser stabilization system (see below).
21
LIGO M030023-00M
We systematically characterized these initial LIGO stacks to establish similarity with the
Livingston instantiations and to explore off-diagonal modes not previously measured. These
measurements allowed development and confirmation of a dynamic numerical model that
predicts the reactance and transmissibility of these fairly complex "payloads" for external forces15
Two variants of an external isolator were prepared for testing, differing principally in their force
actuator technology. The HEPI (Hydraulic External Pre-Isolator) system is based on laminar-flow
hydraulic differential pistons, originally developed by Stanford University16. Eight prototype
actuators and a regulated hydraulic supply system were engineered by a collaboration of
engineers and scientists from Stanford, LIGO Livingston, Caltech and MIT and installed near the
end of 2002 on the LASTI BSC chamber. This system is currently undergoing actuation trials.
A second external actuator variant, dubbed MEPI (Magnetic External Pre-Isolator), was
simultaneously developed at MIT. This alternative may potentially afford lower complexity and
cost than the hydraulic system, at the expense of somewhat lower stroke and force capability. A
suite of eight MEPI force actuators was fitted to one of the LASTI HAM chambers in the third
quarter of 2002 and is undergoing closed-loop control tests. The two-actuator variants share a
common physical mounting, designed for direct compatibility with existing LIGO structural
interfaces. Selection of one of the variants is expected in the first quarter of 2003, to be followed
by intensive development to refine, test and replicate the design for installation at the LIGO
Livingston observatory.
During 2002 the LASTI pre-stabilized laser also served as the development platform for an
improved Pre-Stabilized Laser (PSL) frequency/phase control system. The fielded laser
stabilization electronics operate reliably, but have routinely failed to achieve unity-gain
bandwidths in excess of 200 kHz. This has limited the performance of successive phase and
frequency loops, which depend hierarchically on this initial stabilizer to determine their own
bandwidths. Using the LASTI PSL as a trial platform, modified electronics were developed and
tested; a bandwidth exceeding 1 MHz was achieved along with significant improvements in
robustness and reliability. These developments are now being engineered into an upgrade for the
observatory laser systems, slated for installation in the second quarter of 2003 17
Finally, during 2002 LASTI scientists wrapped up characterization of a full quadruple-pendulum
Advanced LIGO suspension mockup. This prototype, with metallic dummy masses and wires in
place of the eventual sapphire and silica mirrors and fibers, was assembled by collaborating
scientists from University of Glasgow, Caltech and MIT in the LASTI high bay and tested to
validate dynamical and control models. Several iterations to both the mechanical system and its
simulation brought them into sufficient agreement to develop a refined design for the advanced
mirror suspensions. This design is now in fabrication at Caltech, and a first article is scheduled for
delivery to LASTI in the first quarter of 2003.
The LASTI, along with the Caltech 40 meter prototype, forms the backbone of the Advanced
LIGO R&D program. Each subsystem’s critical elements are tested in a realistic environment,
allowing verification of the principles of operation as well as details of installation and
implementation. When possible, the subsystem interfaces are tested, along with cabling and
other constraints. The objective is to minimize the risk in cost and schedule when we reach the
point of installation and commissioning at the Observatories through a thorough prototyping cycle.
“Vibrational Modes of the BSC Seismic Isolation System,” T020046; “Vibrational Modes of the
HAM Seismic Isolation System;” Hytec Inc., 1998, T020045
16 S. Peirce, H. Tran, M. Wiedemann, and D. DeBra, “Quiet Hydraulics for Ultraprecision”
Actuation,” in Proceedings of ASPE Spring Topical Meeting on Mechanisms and
Controls for Ultraprecision Motion, Tucson Az., 1994.
17 McKenzie, Rollins, Ottaway & Zucker, T020097-00-D, LIGO-T030012-00-D (in preparation)
15
22
LIGO M030023-00M
Research and Development toward Advanced LIGO
This year we initiated or continued a broad range of research and development to support the
Advanced LIGO concept. This effort is very strongly collaborative, and the highlights of the
progress in 2002 described below are often the result of collaborations with other institutions in
the LIGO Scientific Collaboration (LSC).
Seismic Isolation
The seismic isolation team focused on the pre-isolator development for initial LIGO described
above. This advance implementation of the pre-isolator is, in addition to an important near-term
aid for the Livingston interferometer, also a significant step forward for the Adv LIGO seismic
isolation system. A photograph of the hydraulic-actuator variant is shown in Figure 7.
Figure 7 Hydraulic pre-isolator (HEPI) vertical isolator. On the left, the vertical
actuator is shown; differential pressure in the bellows exerts force on the septum in the
middle, which is carried to the load via the pyramidal flex joint at the top. On the right,
the actuator is shown as installed at the MIT LASTI testbed.
A second-generation active isolation system prototype was designed by the LSC team and
fabricated by the LIGO Laboratory. It is currently being commissioned at the Stanford Engineering
Test facility. A photograph of the prototype is shown in Figure 8. This technology demonstrator
will be used to (a) inform the development of the full-scale LASTI seismic systems for the HAM
and BSC chambers, which will be developed this coming fiscal year and (b) serve as a controls
test bed for the active isolation systems. Initial testing of the demonstrator show that a key
measure of intrinsic mechanical alignment, the coupling from a requested horizontal actuation to
an accidental tilt of the platform, is very low, which will ease the low-frequency controls design.
Other measurements indicate that the first internal mechanical resonance, which will limit the
maximum control loop bandwidth, is roughly 200 Hz, compatible with the design goal of 50 Hz for
the loop bandwidth.
23
LIGO M030023-00M
Figure 8 Photograph of the prototype at the Engineering Test Facility (ETF), at
Stanford, of the in-vacuum seismic isolation system. The trapezoidal springs which
support the outer and inner stages can be seen; the cavity at the lower left is one of six (3
outer, 3 inner) cavities that receive a plug-in unit containing sensors and actuators
Testing and control law development will continue on this system during 2003. A request for bid
for the next generation prototype is in preparation and will be issued in early 2003, enabling the
delivery to LASTI in late 2003.
Suspensions
An all-metal test mass quadruple suspension prototype was developed at the University of
Glasgow GEO lab and then sent to MIT for testing. All of the solid body modes were identified,
and the model for the suspensions developed at Caltech, Stanford, and Glasgow was refined.
Further trade studies on the lengths and masses were made based on the updated model. A
challenge in the design is to damp the solid-body modes of the suspension without introducing
excess noise in the gravitational-wave band (10 Hz and higher). Several approaches are being
followed: using passive eddy-current damping, development of a miniaturized interferometric
sensor, and an approach using a split feedback system has been developed in VIRGO 18.
An analysis of the thermal noise of tapered fused silica fibers at Caltech showed that this is an
attractive alternative to ribbons for ease of fabrication and ultimate thermal noise performance.
Some first samples have been fabricated for tests. Development of ribbons continued at Glasgow
as the baseline design. Refinement of the attachment technique of the fused silica suspension
fibers to the masses, using hydroxy-catalysis bonding, to sapphire (for the test mass) and highdensity glasses (candidate for the penultimate mass) was made with good success.
18
VIRGO, French-Italian gravitational-wave detector and consortium, http://www.virgo.infn.it/
24
LIGO M030023-00M
We have completed the design and fabrication of the first prototype auxiliary optics suspensions;
see Figure 9. This suspension design carries the mode-cleaner optics, and will first be exercised
at Caltech to check the solid body modes and damping characteristics, and then transferred to
the MIT LASTI facility to look at installation and control issues.
Figure 9 Photograph of the prototype of a triple suspension design for the Mode Cleaner
mirrors. The dummy optics is made of aluminum with holes bored to match mass and
inertia for the final silica optics. The prototype has coil actuators on all three levels,
identifiable as white ceramic cylinders.
A significant step in 2002 was the installation of the complete set of triple-pendulum fused-silica
fiber suspensions in the GEO-600 interferometer by the GEO project. The Advanced LIGO
suspension design is directly derived from the GEO-600 design, and the test of fabrication,
installation, and now ultimately performance of the working design will be invaluable for refining
the Advanced LIGO design.
25
LIGO M030023-00M
Optics
We made significant progress in producing and characterizing sapphire as the preferred test
mass material for Advanced LIGO. Our industrial partner fabricated full-sized boules (see Figure
10) that will now be polished to allow a more complete characterization.
Figure 10 Sapphire substrate pathfinder. This piece, fabricated by Crystal Systems, Inc.,
is the full size of an Advanced LIGO test mass, 32 cm dia, 40kg mass. (Courtesy Insaco)
To address absorption of the substrate of the 1-micron laser light, annealing processes were
refined in collaboration with Stanford, resulting in promising reductions. Industrial partners
successfully pursued approaches to compensating for inhomogeneity. The notion is to polish a
surface, which has features complementing the defects in transmission, on the anti-reflection side
of the optic using two different approaches. One (Goodrich) involves a small rotary abrasive tip
and an x-y table; the other (CSIRO) uses an ion-milling technique. Both can bring the net optical
path seen by the light to an acceptable level. In parallel, manufacturers were able to produce
material with improved homogeneity.
The Thermal Noise Interferometer (TNI) research at Caltech produced its first preliminary results
with fused silica test masses, and noise hunting and noise reduction is underway.
Optical Coatings
One important measure of the optical coatings is the optical absorption. Acceptable (sub-ppm)
losses have been demonstrated this year with conventional coatings by several vendors.
We pursued a strong LSC/LIGO Laboratory program this year to identify the magnitude and
source of coating mechanical losses, and to improve the model of the coating thermal noise. The
mechanical losses lead to thermal noise; the coating is an important contributor due to the
geometry of the test mass, coating, and laser beam, There is a limited choice of materials and of
processes which lead to both low mechanical and low optical losses. We are executing a program
26
LIGO M030023-00M
to identify the source of loss and to explore alternative coating materials and processes that meet
the combined optical and mechanical requirements.
Significant progress has been made: We were able to demonstrate the source of the mechanical
losses in the coating. The high-index tantalum material, rather than the low-index material or
interfaces, is responsible. We are now pursuing alternative coating materials with several vendors
with incremental progress in reducing losses.
Thermal Compensation
The initial prototyping of the two schemes for thermal compensation concluded this year and
resulted in the PhD thesis of a LIGO student19. The lens formed in the substrates due to the
absorption of the laser light in the substrate make the interferometer sensitive to the power level.
Including a thermal compensation system allows the interferometer to be used with a wide range
of input powers, allowing e.g., better low frequency sensitivity with a reduction in the power. It
also allows a trade to be made with the material properties of the substrate; this is useful for
sapphire, and necessary in the fallback case of fused silica.
The basic approach for compensation is to add a complementary additional heat source, so that
the sum of the laser and compensation heating leads to a uniform optical path. In one technique,
a circular heater adds heat to the edge of the optic. In this way, the scattering effect of lensing
can be reduced (in experiments and models, which show excellent agreement) by more than a
factor of 50; see Figure 11, upper plots. This is a very effective approach for the case of uniform
absorption, which is expected to dominate.
R. Lawrence, “Active Wavefront Correction in Laser Interferometric Gravitational Wave Detectors,”
MIT Ph.D Thesis, 2002, P030001-00-R
19
27
LIGO M030023-00M
Figure 11 Thermal compensation demonstration results. Top left: The contour map for a
uniform absorption of a Gaussian beam. Top right: The residual deformation after
compensation with a ring heater. Bottom left: the distortion due to a ‘point absorber’
(mimicked by a small probe laser beam); Bottom right: the map after compensation with
a scanned compensation beam.
In the second approach, a scanning laser beam is played on the substrate and the dwell time
and/or intensity can be modulated to deposit heat in a pattern optimized to compensate for a
specific defect, for example a volume of higher thermal absorption. As shown in the lower plots in
Figure 11, an additional suppression of a factor of 8 can be achieved for this example of point
defect.
Pre-stabilized Laser
The programs to develop 200 W laser sources continued at Adelaide, Stanford, and Hannover.
During this year, each group has built up a prototype of their approach to making the high-power
head: an injection-locked end-pumped rod design from Hanover, an injection-locked stableunstable slab in Adelaide, and a slab amplifier at Stanford. The near-term goal is to make a
selection based on a set of criteria developed at Hannover, one of which is to produce 100 W by
February 2003. Greater than 90 W have been produced in several designs, although not in the
final configurations; see Figure 12 for an example output curve for a linear resonator using the
Hannover approach.
28
LIGO M030023-00M
multimode Resonator ( M2 < 7 , OC = 12% )
100
non polar ized
90
%
2
C
O
R
H
B
Pe
5
Q
a
X
5
tprR
rfi3
e
l8
d
n
u
b
m
b
e
1
0
W
p
o
y
s
ic
t4
w
h
a
c
output power [W]
80
70
60
50
40
30
20
50
100
150
200
250
pum p power / Head [ W]
Figure 12 Laser Zentrum Hannover early prototype of a high-power laser head in a
linear cavity configuration (at left). The final configuration is a ring-resonator. At right,
the power output of the system as a function of the pump light input power; the system
approached the initial goal of 100 W.
Input Optics
The University of Florida and their collaborators made progress on the challenges in the Input
Optics subsystem. A novel Faraday Isolator design was developed which uses a pair of crystals
in a compensation technique to deliver high isolation at high powers. In this design shown in
Figure 13, two 22.5° Faraday rotators and a reciprocal quartz polarization rotator placed between
them replace the traditional single crystal 45° Faraday rotator. In such a configuration,
polarization distortions that a beam experiences while passing the first rotator will be
compensated in the second. Tests to the maximum power available are encouraging.
29
LIGO M030023-00M
-20
-25
Conventional FI
-30
Isolation
-35
Ratio
(dB opti cal) -40
-45
Compensated Design
-50
-55
0
204
0
608
0
100
Laser Power (W)
Figure 13 Top: compensated Faraday isolator design. Bottom: isolation for a
conventional and the compensated designs.
We favorably reviewed the Input Optics Design Requirements prepared by the group at the
University of Florida, and the group was given approval to proceed to the preliminary design.
Systems and Interferometer Sensing and Control
We refined the baseline design and conducted a System Design Requirements Review. A
number of subsystem requirements and trade studies were concluded. We initiated a study of the
data readout approach for the signal-recycled interferometer. The preliminary result is that the DC
readout (in contrast to the traditional RF-modulation technique) appears to take advantage of the
coupling that exists in a signal-recycled interferometer between the shot-noise fluctuations and
the photon pressure on the test masses. We have also been working with industry to develop a
low noise Digital-to-Analog Converter (DAC). Test results on the first prototypes should be
available before the end of this year.
30
LIGO M030023-00M
LIGO Scientific Collaboration (LSC)
The LIGO Scientific Collaboration20 (LSC) is the means for organizing technical and scientific
research in LIGO. Its mission is to insure equal scientific opportunity for individual participants
and institutions by organizing research, publications, and all other scientific activities.
It includes scientists from the LIGO Laboratory as well as collaborating institutions. The
organization is separate from the LIGO Laboratory, with its own leadership and governance, but
reports to the Laboratory Directorate for final approval of its research program, technical projects,
observational physics publications, and talks announcing new observations and physics results.
The March 2002 LSC meeting was held at the Livingston Observatory. In conjunction, Louisiana
State University (LSU) hosted a symposium honoring Bill Hamilton. Numerical relativists with an
interest in collaborating with LIGO and LISA made presentations and participated throughout the
LSC meeting. LIGO-LSC and the numerical relativists initiated plans for useful activities that will
support LIGO observational programs and guide theoretical research.
The eleventh meeting of the LIGO Scientific Collaboration (LSC) was held at the Hanford
Observatory August 19-23, 2002. The significance of the upcoming science run and the
organization of the subsequent data analysis effort were discussed. The schedule for Advanced
LIGO was also presented.
The first science run (S1) included active participation from LIGO Laboratory scientists and staff
but also, in numerous ways, from the broader community of scientists composing the LSC. LSC
scientists contribute to real-time monitoring of the interferometer data for detector diagnostics and
conduct analyses of the data.
The LSC scientists, as members of “upper limits” groups, pioneer the analysis of LIGO data in the
search for gravitational waves. Several of these collaborating groups perform real-time searches
using computers at the observatories. These searches are useful in providing rapid feedback to
the control room on any instrumental pathology that might mimic a true gravitational-wave source.
Keeping the LIGO interferometers running smoothly and continuously requires a cadre of skilled
operators at each site, working in teams on rotating shifts. The operators must bring the
interferometers into lock, tune the alignment and gains to optimize sensitivity, and try to preserve
those optimum conditions. Beyond operating the interferometers, the quality of the science data
must be assured. This requires a parallel implementation of scientific monitoring shifts.
LSC scientists have been staffing the scientific monitoring shifts. The scientists serve as “science
monitors” who focus on ensuring that the interferometer data is of the highest quality. Since the
monitors start with diverse specialties and backgrounds, formal training was instituted for bringing
new participants up to speed. An expert monitor is paired with a “trainee,” a pattern that began
back in November 2000. As a result, the pool of science monitor experts has steadily increased.
This will be essential to support the anticipated periods of steady state, multi-month data runs.
More than 180 eight-hour shifts were staffed by scientists from Caltech, Carleton College, the
University of Florida, Hanford Observatory, Livingston Observatory, Louisiana Tech., the
University of Southeastern Louisiana, Loyola University, Louisiana State University, the University
of Michigan, Massachusetts Institute of Technology, the University of Oregon, Pennsylvania State
University, the University of Rochester, Syracuse University, the University of Texas at
Brownsville, Washington State University–Pullman, and the University of Wisconsin-Milwaukee.
20
http://www.ligo.org
31
LIGO M030023-00M
Just prior to the start of S1, several of the upper limits groups verified that an emulated
gravitational-wave signal could be detected in the data. They simulated the response of the LIGO
mirrors to a variety of gravitational waveforms, allowing downstream confirmation that the signal
did indeed appear as expected.
We have scheduled the next LSC meeting at Livingston, March 17-20, 2003. At this meeting,
results from the S1 data analysis will be discussed; the pre-stabilized laser head downselect will
be presented; and a preliminary assessment of sapphire/fused silica test mass downselect data
will be made.
32
LIGO M030023-00M
Astrophysics and Data Analysis
The work on astrophysical data analysis is an LSC activity with a strong Laboratory contribution.
The present effort is organized into four groups, with the objective of setting interesting upper
limits on the flux from short-term burst sources, stochastic sources, binary inspiral ‘chirps’, and for
continuous-wave sources.
Searches for Un-Modeled (Burst) Sources
The LSC Bursts Working Group (BWG) pursues the search for gravitational wave bursts in LIGO.
The group has more than 40 members from LIGO and the LIGO Scientific Collaboration (LSC).
The goal of the BWG is to look for short transients (lasting less than one second) of gravitational
radiation of unknown waveform. These include burst signals from supernovae and black hole
mergers for which the physics and computational implications are complex enough that make any
analytical calculation of the expected waveforms extremely difficult. The detailed knowledge of a
signal waveform would have allowed the use of matched filtering which is the optimal detection
technique; this is something that falls outside the goals of the BWG and the Inspiral Working
Group rigorously pursues it. Only general considerations regarding the duration and the
requirement for the signal to have significant strain amplitude in LIGO's sensitive frequency band
are made and general time-only domain and time-frequency domain search techniques are
employed. These aspects of search strategy make the search for bursts with LIGO open to any
unanticipated source of gravitational radiation that falls under the general time-frequency
considerations, an issue that should not be neglected in these early stages of gravitational wave
astronomy.
An additional focus of the BWG is to look for correlations of gravitational wave bursts with -ray
bursts (GRBs). A number of GRB progenitors are plausible gravitational wave burst emitters and
a comparison of the correlation function of the LIGO detectors immediately before a GRB (“on
source”) and at random times (“off source”) may statistically establish their association 21.
Finally, the BWG plans to integrate the GEO and LIGO data in a single analysis making the most
out of a multi-detector coincidence analysis.
The LIGO S1 run reflects an integrated ~96 hours of coincidence observation with the three LIGO
detectors. The gravitational wave channel, AS_Q, was analyzed within the LDAS (LIGO Data
Analysis System) environment after it was whitened. Three main astrophysical search algorithms
were employed for the detection of bursts; these are referred to as Event Trigger Generators
(ETGs) and, technically, they are Dynamical Shared Objects (DSOs) running within LDAS.
The “SLOPE” ETG is a time-domain algorithm (commissioned by Ed Daw and inspired by Arnaud
et al.22 that fits the AS_Q time series to a least-squares line and selects candidate events based
on the value of the slope. The algorithm reports the start time and significance (value of the
slope) of the excursion.
The “TFCLUSTERS” ETG is a time-frequency method (developed and commissioned by Julien
Sylvestre23) relying on successive spectrograms taken every 0.125 seconds, which are then
subjected to a threshold to identify time-frequency tiles (“pixels”) with statistically significant
excess of power. These pixels are then clustered and the total power, central frequency,
bandwidth, start time and duration of the formed cluster are reported.
21
Finn et al., Phys. Rev. D 60, 12110 (1999)
Arnaud et al., Phys. Rev. D 59, 82002 (1999)
23 J. Sylvestre, gr-qc/0210043, to appear in Phys. Rev. D
22
33
LIGO M030023-00M
A third method, “POWER24” uses, like “TFCLUSERS”, Fast Fourier Transforms to calculate power
spectra of the raw time series for any given start time and duration. The algorithm then compares
the power in the data over every user-defined time-frequency tile to the statistical distribution of
noise power. A burst signal is detected if the excess of power is greater than expected from the
statistical fluctuations of the noise. For each search method the candidate bursts and their
features were stored in the LDAS database.
At the same time, a set of interferometer and environmental channels (with insignificant or null
coupling to gravitational radiation) were analyzed within the DMT (Data Monitoring Tool) for the
identification of transients of non-astrophysical origin, i.e., glitches attributed to the instrument and
its environment. Following some high-pass filtering (typically 30Hz cut-off), glitch-finding methods
based on time-over-threshold (both in absolute -ADC counts- and relative -sigma- sense)
methods were invoked in identifying the start time, duration and significance of non-astrophysical
transients. These defined the so-called veto triggers and their temporal coincidence with
gravitational wave event triggers resulted in excluding the latter from further consideration. The
use of vetoes in the burst analysis pipeline was thus able to reject a significant fraction of the
candidate events at the cost of relatively small loss of detector lifetime.
Requiring their temporal coincidence in the three LIGO interferometers attained further reduction
of the remaining candidate events. A transient signal of astrophysical origin is expected to yield
time-correlated triggers in the three LIGO detectors subject only to the propagation time between
the sites and any dispersion introduced in establishing the burst time via the search algorithms.
Further correlation in burst duration, frequency band and amplitude as well as that of the raw time
series themselves between the sites is to be expected.
So far we have employed only the temporal coincidence of burst triggers across the three LIGO
interferometers as well as the frequency band matching for the event trigger generators
performing a time-frequency analysis. The exploitation of the full power of the multi-detector
search for bursts is expected to take place in the near future.
A central element in analyzing the S1 data has been the definition of ~10% of the S1 coincidence
data as the “playground” set. In order to avoid any statistical biases in the search for bursts, we
have allowed any tuning involved in setting the search algorithm and veto parameters to be
performed only on this set. Once this was done, the analysis was applied to the remaining ~90%
of the S1 coincidence data.
The bursts analysis pipeline we have just described was applied to the S1 triple-coincidence data
and an upper bound on the rate of events observed by the three detectors was established using
the unified approach on setting upper limits of Feldman and Cousins 25. A full set of Monte Carlo
simulations was also used to inject Gaussian and sine-Gaussian signals of variable strength,
width and frequency content onto the real interferometer time series. This allowed us to establish
the efficiency of the entire bursts analysis pipeline to selected ad hoc benchmark bursts. We were
thus able to translate the bound on the event rate to an exclusion plot of fluxes versus strength of
gravitational wave bursts originating from fixed strength sources positioned on a fixed sphere
centered on earth. These plots will be released as soon as the bursts analysis is internally
reviewed and approved by the entire LIGO Scientific Collaboration (LSC). A richer interpretation
invoking astrophysics motivated signal waveforms as well as source depth and angular
distributions are currently being worked on and will be reported in the near future.
24
25
Anderson et al., Phys. Rev. D 63, 042003 (2001)
Feldman and Cousins, Phys. Rev. D, 57(7), 3873
34
LIGO M030023-00M
Search for a stochastic gravitational wave background
Stochastic backgrounds are signals produced by many weak incoherent sources. They are nondeterministic and can only be characterized statistically. Such signals can arise from earlyuniverse processes (analogous to the electromagnetic CBR) and from present-day phenomena.
They give rise to a (probably stationary and Gaussian) signal that is correlated between the two
detectors. It will have the same spectrum in each detector, and is differentiated from detector
noise by its inter-detector correlation, which depends in a known way on the signal spectrum and
the detector separation and orientation. The greatest risk is that similar correlations may be
produced by the (electromagnetic) environment.
Stochastic signals are expected to be quite weak compared to the intrinsic noise of an individual
LIGO interferometer; consequently, detecting or placing a limit on a stochastic gravitational wave
signal will require long observation periods over a bandwidth a few times the inverse light travel
time between the interferometers.
Activities of the Stochastic Upper Limit group have centered on the analysis of two data collection
runs, the E7 and the S1 science run. During these runs, the LIGO Hanford and LIGO Livingston
Observatories recorded coincident data suitable for analysis for stochastic gravitational wave
sources. More detailed information is available in the group's E7 26 and S127 reports. However,
vetted science results are not yet available from S1 analysis.
GEO600 also took coincident data with LIGO detectors during the E7 and S1 runs; however,
GEO/LIGO correlations are not reported on here. Although a GEO-LIGO correlation will not
improve the upper limit by much due to the small overlap between the GEO and LIGO
interferometers, it will provide insight about any inter-continental cross-correlated environmental
noise. The ALLEGRO28 resonant bar detector took data in three different orientations during E7.
Analysis of these data will not be reported on here.
The search for a stochastic background of gravitational radiation in the E7 and S1 data employs
the standard optimally filtered cross-correlation technique. We have summarized this procedure
in a LIGO technical document29.
For the S1 data analysis, 7.5 hours of triple coincidence (L1-H1-H2) data were set aside for
stochastic upper-limit playground analyses. These data were purposely chosen to be scattered
throughout S1, and to represent "typical" instrument performance (both bad and good). All
investigations that could bias our final upper-limit on the stochastic background signal strength
were initially performed on the playground data.
In addition, simulated stochastic background signals were injected into two 1024-second
stretches of post-S1 data in the Hanford 2-km and Livingston-4km interferometers. The hardware
injections allowed us to test the full data analysis pipeline-from mirror movement to upper-limit
values-for large SNR signals where we knew (a priori) the expected results.
In an actual search for a stochastic background signal, we work with discretely sampled data
broken up into segments T = 90s in length. Within the LIGO data analysis system (LDAS), we
request the gravitational wave data in 15-minute chunks (each 15-minute chunk representing a
single job), originally sampled at 16384 Hz. We then down-sample the data to 1024 Hz for LHOLLO correlations (2048 Hz for H1-H2 correlations), and estimate power spectra for each detector,
26
http://www.phys.utb.edu/stochastic/, "E7 report"
http://www.phys.utb.edu/stochastic/, "S1 report''
28
W. O. Hamilton et al., "Resonant detectors and interferometers can work together," Proceedings of the
SPIE conference, Hawaii, 2002.
29 “Detecting a Stochastic Background of Gravitational Radiation - Background Information,” LIGO
Technical Document, http://www.ligo.caltech.edu/docs/T/T020166-00.pdf.
27
35
LIGO M030023-00M
which are used in the calculation of the optimal filter for a stochastic background with gw(f) =
const := 0.
Within the stochastic search code, we calculate instrument response functions, which are valid for
the particular job we are analyzing. We then split the data into 10 (90-second) segments, each of
which is windowed in the time domain, zero-padded to twice its length, and discrete Fouriertransformed. A value of the optimally filtered cross-correlation statistic is calculated for each T =
90-sec segment, while the theoretical variance is calculated only once for the whole 15-minute
job. For each 15-minute job, we calculate the sample mean, and sample standard deviation of the
10 cross-correlation statistic values. Finally, we then form a weighted average to obtain a point
estimate of the stochastic background signal strength. Frequentist methods are used to convert
the composite cross-correlation measurements to limits on gw(f)×h1002.
As an example of the expected 90% confidence level upper-limits for a pair of LIGO
interferometers, we consider H2-L1. An upper-limit was calculated, solving for gw(f) = const in
the 40Hz - 265Hz frequency range, with SNR set to 1.28 (for 90% confidence), and typical S1
power spectra substituted for P1f) and P2(f). The observation time (corresponding to the amount
of clean, coincident H2-L1 S1 locked data) was 100h, resulting in an expected upper limit of
gw(f) x h1002 < 15. This serves to set the scale of expected performance for the LIGO
interferometers during the S1 run.
Simulated stochastic background signals with gw(f) = const were injected into two 1024-sec
stretches of post-S1 data in the LHO and LLO interferometers (so-called hardware injections).
gw(f) x h1002 = 24414 and 3906 for these two injections, corresponding to SNRs of roughly 10
and 5 in a 15-minute observation. The effect of these two hardware injections on the power
spectral densities of the interferometers is evident as excess noise in the injected frequency
band.
Averages of the point estimates of gw(f) x h1002 as produced by the stochastic DSO analysis
software for the times of the hardware injections fall within one or two standard errors of the
injected point estimate, giving us confidence that the full data analysis pipeline is working as
expected.
In addition to performing the hardware injections, we are able to inject via software simulated
stochastic background signals into the data. Functionality exists within LAL to simulate stochastic
signals (with power law dependence gw(f) = f) for the LHO and LLO interferometers, convolved
with the appropriate instrument response functions. Results of the stochastic DSO analysis of
software injections were consistent with that of the hardware injections, up to an overall sign. It is
interesting to note that this comparison of hardware and software injections first discovered an
overall sign difference between the interferometer transfer functions of LHO and LLO, which was
subsequently measured and confirmed at the sites.
We are also studying a hierarchical approach in collaboration with IUCAA, Pune, India. We have
defined and prototyped an improved hierarchical scheme in searching for inspiraling binaries. The
earlier hierarchical scheme developed by Mohanty and Dhurandhar used the two masses of the
constituent stars for implementing the hierarchy. This scheme is being currently implemented into
LAL in order to make the algorithm available for the next phase of LIGO science runs. The
improved scheme extends the hierarchy to yet another parameter, namely, the time-of-arrival, so
that the hierarchy is now in three parameters. This procedure is expected to reduce the cost by a
factor of 4 or 5 over the Mohanty-Dhurandhar search and by a factor of about a 100 over the flat
search. The algorithm and its prototyping results have been discussed in several conference
proceedings30,31 and is pending publication32.
30
31
Amaldi Conference 2000.
GWDAW 2002
36
LIGO M030023-00M
Search for Binary Inspiral signals
The Inspiral Upper Limit Working Group is focussed on the search for gravitational-wave “chirps”
emitted by compact binary systems as the bodies spiral ever closer to one another and ultimately
coalesce. The group’s charter is to extract astrophysically significant results (presumably upper
limits rather than detections) from early LIGO data, collected while the detectors have modest
sensitivity. So far, the group has focused on low-mass systems, including binary neutron star
systems (in which each body is expected to have a mass of ~1.4 solar masses).
We search for gravitational wave signals from binary inspirals in the LIGO data using matched
filtering. This method uses linear filters constructed from the expected waveforms that are
computed using post-Newtonian methods. The waveforms used to generate the filters in this
analysis are the stationary phase approximation to the Fourier transform of the second postNewtonian order. We neglect spin effects. This gives a two parameter family of waveforms; the
parameters being the masses of the objects in the binary system. We further restrict the binary
systems to circular orbits. These waveforms are known as 2pN inspiral chirps.
The group began its work in earnest in early 2002, using data from the E7 engineering run to
develop data analysis procedures and to explore ways of using environmental and instrumental
auxiliary channels to identify transient disturbances in the detectors, in order to “veto” false
gravitational-wave candidates. One of the key concepts introduced was to set aside a small
fraction of the data as a “playground” in which analysis cuts and veto conditions can be studied
and tuned freely; then, after freezing all details of the analysis, the final result can be extracted
from the remainder of the data without fear of human bias. The main gravitational-wave inspiral
search uses the standard technique of optimal Wiener filtering with a bank of inspiral templates
covering the mass parameter space of interest, utilizing code from the LIGO Algorithm Library
(LAL) and using the job control, data conditioning, parallel processing, and database functionality
provided by the LIGO Data Analysis System (LDAS). In addition, an exploratory analysis was
done using the Fast Chirp Transform (FCT) algorithm running within LDAS.
In September, the focus of the group naturally shifted to the greatly improved data from the S1
science run, in which binary-neutron-star inspiral signals are detectable to a greater distance than
ever before.
Matched filtering requires a good set of template waveforms that accurately predicts the possible
signals. Ideally the signal from a binary inspiral would be computed from an exact two-body
solution to the Einstein equations for the general relativistic gravitational field. However, the exact
two-body solution is not known and one must use some kind of approximation. We use the
restricted second-post-Newtonian (2PN) Taylor-series approximation to waveforms for nonspinning compact (point) objects in quasi-circular orbits. Restricted 2PN means that the amplitude
is computed only to leading order in GM/rc2 (where M is the total mass and r is the orbital
separation in harmonic coordinates), while the phase evolution of the waveform is computed to
two orders in GM/rc2 beyond leading order. The waveform phase can be approximated, in this
case by a Taylor series, in either the time domain or the frequency domain. Since the difference
between these two approximations can give us some idea of the errors due to the failure of the
post-Newtonian approximation in the late stages of inspiral, we use both: The template bank and
the actual templates used to filter the data are constructed using the frequency-domain
approximation, and the injected waveforms used to test the efficiency of the analysis use the
time-domain approximation.
As an additional pathology check, we compute the overlap of each template — put into the
frequency domain with a discrete FFT — with a stationary-phase approximation of itself in the
32
http://www.ligo.caltech.edu/docs/P/P020015-01.pdf
37
LIGO M030023-00M
frequency domain. Since the stationary phase approximation is known to go bad only when the
post-Newtonian expansion goes bad, this is an independent and tighter check that sidesteps
issues of time-domain vs. frequency-domain approximations. We find that the overlap is below
90% for binaries of M > 2.5Mo with the H2 noise curve and much better for the others. The
physical reason for this is that the frequency of the last circular orbit, about when the merger
waveform begins, is in the interferometer’s sensitive band for such high masses.
The IUL detector characterization sub-group initially considered all control channels and all PEM
channels as possible sources for vetoes. The approach adopted for S1 built upon experience
developed during the E7 analysis. Numerous software tools were used to examine the data; DMT
programs, home made MATLAB scripts, and examination by eye using DTT. In the E7 analysis
there was much hope that a smoking gun would be found among the observatory Physics
Envionmental Monitor channels. Virtually all of the accelerometer, seismometer, microphone, and
voltage line monitor and magnetometer channels were examined. After a careful search,
however, we found that the inspiral-template-based L1: LSC-AS I veto (the interferometer
antisymmetric output signal, demodulated at 90 degrees to the strain channel) does the best job
with moderate dead time.
The group is now in the process of refining the analysis, especially in the areas of applying
appropriate auxiliary-channel vetoes and modeling the spatial distribution of sources in the Milky
Way, so that the efficiency of the search can be calculated accurately. The group expects to
publish at least one result in 2003 based on the S1 data.
Search for Periodic signals
The primary astrophysical candidates for periodic emission of gravitational waves are spinning
neutron stars, either isolated or in binary systems. Continuous gravitational waves are emitted
from these candidates when there are asymmetries due to either rotation about a nonsymmetry
axis, precession, or stellar pulsations. A subset of these objects is observed in the
electromagnetic spectrum, for example as pulsars or in x-ray binary systems. A further subset of
these objects spins fast enough to put their potential gravitational wave emission frequency into
the LIGO and GEO band. (For the simplest case the gravitational wave frequency is emitted at
twice the spin frequency.) However, there should be many more neutron stars than those
observed, and there is always the possibility of an unknown class of periodic sources. Thus, both
targeted and untargeted searches are warranted. Targeted searches include known pulsars, for
which the position, spin frequency, and spin evolution are known, and low-mass x-ray binaries,
for which the position is known, but a search over a limited frequency band and orbital
parameters is needed. Targeted searches could also include a targeted set of positions on the
sky (such as that of a globular cluster or the galactic center) for which a search over the other
signal parameters is needed. Untargeted searches involve a search over many sky positions and
intrinsic source parameters. Note that in addition to intrinsic source evolution, the changing
velocity and orientation of the detector relative to the source induces amplitude and phase
modulations into the data. And since periodic signals are expected to be weak, long observation
times are required for detection. An untargeted search is very interesting, but doing so using
coherent techniques (i.e., tracking the phase of the signal, such as in matched filtering) is
computationally expensive in terms of the required CPU cycles. Incoherent and hierarchical
methods must be used to make the untargeted searches feasible. Note that all incoherent and
hierarchical searches invoke coherent methods as part of their strategies. Targeted searches
using coherent techniques are computationally affordable and relatively easy to implement
compared with untargeted searches. Targeted searches are of interests in their own right, but
also much of the code developed for a targeted search can be used in an untargeted search as
well, making this an important first step in that direction.
In the last year PULG has consider four types of searches. Each search is described briefly
below.
38
LIGO M030023-00M
Time Domain Searches for Signals from Known Isolated Pulsars
The time domain analysis is based around the idea of heterodyning—unwinding the expected
phase of the pulsar signal by multiplying (mixing) the data with a complex function of the form
exp(-2π ift), where f is the expected frequency of the gravitational wave signal. The procedure is
done in several steps of heterodyning, filtering, and down sampling of the data. This reduces the
volume of data by factors of about 106, which is of great practical importance in data
management. If carried out with the right pulsar timing parameters, the only time-varying quantity
remaining in the signal left in the data is the antenna pattern of the interferometer, which varies
on timescales of a day. The procedure should, by the central limit theorem, give the noise a nearGaussian probability density. This is checked very carefully, and if satisfied, the probability of the
data for sets of signal parameters is found using chi-squared. Standard Baysian statistical
techniques are used to assign posterior probabilities to the parameters. Using fake data and
injections of fake signals into real data has validated this code. This code has been used in the
preliminary analysis of LIGO and GEO S1 data.
Frequency Domain Searches For Signals from Known Isolated Pulsars
The frequency domain analysis is being implemented both as a stand-alone code and as a DSO
under LDAS. Both the stand-alone code and a stand-alone version of the DSO have also
been used as a test-bed for distributed grid computing under the GriPhyN project the DSO in
conjunction with LDAS. Both realizations use match filtering to coherently sum the data to extract
the signal, correcting for phase and amplitude modulation. The output of the matched filtering
code is the optimal statistic, defined as the F-statistic; F is derived using the principle of maximum
likelihood. The scheme involves two steps. Step 1 is to split the observation time into shorter
segments and generate a Short-time Fourier Transform (SFTs) for each segment using ordinary
FFT routines. Step 2 is to input the SFT data for a narrow frequency band of interest from all the
SFTs that cover the observation time and to send this data into the LAL functions that calculate
the F-statistic. A Monte Carlo simulation that injects signals into the real data finds the distribution
of F, and classical statistical analysis is used to find confidence intervals or upper limits on the
signal amplitude. (The estimated parameters that maximize F can also be computed; this has not
yet been implemented.) Some Monte Carlo simulations have been completed. This code has
been used in the preliminary analysis of LIGO and GEO S1 data.
Blind Unbiased Incoherent Searches
An “unbiased” all-sky search for sources of periodic gravitational radiation is under way.
It is unbiased in the sense that few assumptions are made about the nature of the sources. In
particular, no attempt is made to track the phase of such a source over extended time intervals.
The technique used is based on incoherent averaging of one-sided power spectral density
estimates, that is, on averaged periodograms. Incoherent averaging is generally less sensitive to
weak sources than is coherent integration, but its reduced computational load permits a search
over the entire sky, and the phase-insensitivity of power averaging makes the technique robust
against uncertainties in source parameters. A statistically independent determination of
background noise level is found using nearby (but not quite neighboring) bands to a given narrow
frequency search range. Regions of the spectrum with sharp features, e.g., near a 60 Hz
harmonic will be excluded from consideration or handled (in the long term) with a more
sophisticated algorithm. The effects of the modulations will be determined empirically and
parameterized, as detection efficiency corrections, using Monte Carlo software signal injections.
This search makes use of the SFTs generated for search 2 above. This search method has been
used in the preliminary analysis of LIGO and GEO S1 data.
39
LIGO M030023-00M
Targeted Search for a Signal from the Pulsar in the Binary System ScoX1
The accretion of hot material onto the surface of a neutron star was suggested over 20 years ago
as a possible mechanism to generate quasi-monochromatic gravitational waves. In this scenario
the induced quadrupole moment is directly related to the accretion rate (which can be copious)
allowing the gravitational energy reservoir to be continuously replenished: gravitational radiation
balances the torque due to accretion.
Such scenario has attracted considerable new interest in the past few years and has been fully
revitalized by the launch of the Rossi X-ray Timing Explorer, designed for precision timing of
accreting NS’s. The observational evidence that Low Mass X-ray Binaries (LMXBs) -- binary
systems where a compact object accretes material from a low mass companion -- in our Galaxy
are clustered around a rotation frequency ~ 300 Hz, led Bildsten to propose a mechanism to
explain this behavior. The fundamental idea is that continuous emission of GW’s radiates away
the angular momentum that is transferred to the NS by the infalling material. The fact that the rate
of angular momentum loss through GW’s scales as frequency to the fifth power, provides a very
natural explanation for the clustering of rotation frequency of several sources. The physical
process responsible for producing a net quadrupole moment is the change of composition in the
NS crust, which in turn is produced by the temperature gradient caused by the in-falling hot
material.
Recently, Ushomirsky et al 33 have posed this initial idea on more solid theoretical grounds.
More recently Wagoner has argued that LMXBs could reach a stable equilibrium state by emitting
GW through r-modes, allowing GWs from Sco X-1 and other LMXBs to be potentially detectable
by advanced LIGO. If one of these mechanisms does operate, LMXBs are extremely interesting
candidate sources for Earth-based detectors. Several systems would be detectable by advanced
LIGO, if the detector sensitivity is tuned, through narrow-banding, around the emission frequency.
In particular, Sco X-1, the most luminous X-ray source in the sky, might be marginally detectable
by “initial” LIGO, and GEO600 (the latter in narrow-band configuration), where an integration time
of approximately 2 years would be required.
The implementation of the data analysis scheme follows the frequency domain search for known
pulsars. Code has been developed which generalizes LALDemod in order to take into account
the orbital motion of the source. This code represents the core of the search together with a
function designed to place filters in the space defined by the orbital parameters. At present the
code implementation allows us to search only for binary systems in circular orbits. Some effort is
on-going to generalize the codes to handle the more general case of binaries with nonzero
eccentricity.
33
http://www.arxiv.org/abs/astro-ph/0210175 and references therein
40
LIGO M030023-00M
Outreach
During 2002, the LIGO Laboratory has worked with Jill Andrews (Caltech Assistant to the Provost
for Educational Outreach) and with NSF to plan an enhancement of existing LIGO Laboratory
outreach efforts. LIGO has already conducted an impressive range of local educational outreach
activities at both its Observatories 34.
To leverage previous successful NSF-funded education and outreach (E&O) program experience,
each Observatory Head is recruiting local educators and community leaders who form a “Local
Educators’ Network” (LEN). Focus groups and, as necessary, a more permanent advisory group
will be recruited from the larger group of LEN participants. All existing or planned activities will
undergo assessment in the context of relevance and feasibility by Observatory Heads with their
LEN focus groups. The goal is to develop and maintain long-term, interactive partnerships to
inspire, excite, and motivate a broad spectrum of learners through inquiry, exploration and
experience in science and engineering research. With collective input from our LEN focus groups
(which we expect to underscore outcomes from similar efforts based at Caltech and other
universities) LIGO Observatory Heads will implement a plan that features a balanced set of LIGOrelated educational activities, programs and products with broad impact in formal education,
informal education, and public learning venues.
In November 2002, LIGO presented updated plans NSF. We are submitting a proposal to the
MPS Internships in Public Science Education (NSF 01-39) for continued and supplemental
support of existing and/or new programs in three main areas. These are:
1. Formal Education: Internships in Public Science Education. We plan to seek funds in
order to continue hosting science educators at each Observatory. These educator
interns work with LIGO researchers in developing resource materials and products that
both capitalize on LIGO science and satisfy the needs of local educators.
2. Informal Education: To reach broader audiences, we will seek supplemental resources
and form partnerships in the local communities to create museum-quality exhibits in each
Observatory. We will work to reach teachers and students who are unable to visit the
Observatories by pursuing the resources necessary to create a “Mobile Science Unit,”
and will seek out community youth programs already in place to enhance their programs
with our people and products.
3. Public Outreach: We are planning products such as educational videos for Television,
radio public service announcements or “spots,” and a more interactive website.
Educational Outreach – Hanford
LIGO Hanford Observatory has contributed to the expansion of high-school science education by
directly involving students in LIGO research. This year approximately 70 students from Gladstone
High School (in northwest Oregon) worked on LIGO-related projects throughout the academic
year. On May 28, 2002, students from grades 9-12 described their contributions to LIGO research
to a packed audience of community members at Gladstone High School. (See story at
http://www.ligo.caltech.edu/LIGO_web/0205news/0205han.html for additional details.)
In the summer, a high-school teacher and a middle-school teacher held visiting appointments at
the observatory, helping us to develop in-classroom and informal educational resources. This
work has been disseminated using the "teacher’s corner" web pages (http://www.ligowa.caltech.edu/teachers_corner/teachers.html at LIGO Hanford Observatory.
34
LIGO NSF Proposal for Continuing Operations 2002-2006 (Dec 2000), pgs 24, 84, 165,
http://www.ligo.caltech.edu/docs/M/M000352-00.pdf
41
LIGO M030023-00M
A special emphasis was put on science and math lesson plans in both high-school and middleschool versions, that not only include plans, activities and worksheets, but also the web pages
(http://www.ligo-wa.caltech.edu/teachers_corner/lessons.html) highlight lesson-plan alignment to
the state education standards for Oregon and Washington.
The observatory hosted five undergraduate research students through the REU/SURF program
this summer. Eric Adelberger (University of Washington) gave the LIGO Public Lecture this
summer, entitled "How Many Dimensions Are There to the Universe?” to an enthusiastic
audience of approximately 225 people, ranging in age from pre-teens to retirees.
Approximately 600 visitors toured the observatory this year.
We have formed a Local Educators Network to advise us on future outreach effort. This group
consists of teachers and education professionals, members associated with museums and other
informal education activities, and people actively working with Native American and Hispanic
groups.
Educational Outreach -- Livingston
We continue to be involved in a wide range of educational outreach activities aimed at
communicating to the public what we do in LIGO. Approximately 2000 students and teachers visit
the LIGO site each year as part of school sponsored field trips, and about 1000 adult visitors also
tour the site as part of community and professional groups and as informal participants in weekly
tours for the general public.
We have implemented a summer Research Experiences for Teachers (RET) program that
provides opportunities for teachers to participate in the research activities at Livingston and
simultaneously to develop materials and plans that they can take back to their home schools.
Our Research Experiences for Undergraduates (REU) program continues to grow. This year we
hosted seventeen students participating in Caltech’s “SURF” program or similar REU or summer
programs at LSC member institutions.
We have also hosted several regional workshops for teachers in order to enhance our
interactions with K-12 educators in the region.
LIGO Laboratory and Southern Louisiana University (SLU) exchanged a Memorandum of
Understanding (MOU). LIGO effort at SLU includes improvements of the LIGO end-to-end model
(e2e), and the use of e2e simulation in the education outreach. Prof. Yoshida and his students
have been measuring seismic spectra at the LIGO Livingston Observatory, vital information for
the LIGO simulation. They are analyzing the measured data using the e2e simulation package to
extract more fundamental data for e2e use and to understand the noise due to the beam jitter
caused by mirror motions before the recycling mirror.
42
LIGO M030023-00M
Advanced LIGO Project Book
1. Overview
Insert costs and schedule
Following the initial LIGO scientific observation period, planned for 2003 through 2006, LIGO
detector systems will require an upgrade to significantly improve the detection sensitivity. Such
staged improvements were a central part of the original LIGO design and program plan35.
LIGO consists of conventional facilities and the interferometric detectors. The LIGO facilities
(sites, buildings and building systems, masonry slabs, beam tubes and vacuum equipment) have
been specified, designed and constructed to accommodate future advanced LIGO detectors. The
initial LIGO detectors were designed with technologies available at the initiation of the
construction project. This was done with the expectation that they would be replaced with
improved systems capable of ultimately performing to the limits defined by the facilities.
In parallel with its support of the initial LIGO construction, the National Science Foundation (NSF)
initiated support of a program of research and development focused on identifying the technical
foundations of future LIGO detectors. At the same time, the LIGO Laboratory36 worked with the
interested scientific community to create the LIGO Scientific Collaboration (LSC) that advocates
and executes the scientific program with LIGO 37.
The LSC, which includes the scientific staff of the LIGO Laboratory, has worked to define the
scientific objectives of upgrades to LIGO. It has developed a reference design and an enhanced
R&D program plan. This development has led to this proposal for construction of the Advanced
LIGO upgrade following the initial LIGO scientific observing period.
In this Advanced LIGO Project Book, the definition and conceptual program plan for construction
of Advanced LIGO are described. It is intended that this Project Book will be developed further
and formally maintained as a working baseline definition document for Advanced LIGO.
35
LIGO Project Management Plan, LIGO M950001-C-M
(http://www.ligo.caltech.edu/LIGO_web/ligolab/m950001-c.pdf); LIGO Lab documents can be accessed
through the LIGO Document Control Center (http://admdbsrv.ligo.caltech.edu/dcc/)
36 LIGO Laboratory Charter, LIGO http://www.ligo.caltech.edu/docs/M/M010213-01/
(http://www.ligo.caltech.edu/LIGO_web/ligolab/charter.html)
37 http://www.ligo.org/charter.pdf
43
LIGO M030023-00M
2. Reference Design Baseline Definition
The LIGO Scientific Collaboration, through its Working Groups, has worked with the LIGO
Laboratory to identify a reference design for the Advanced LIGO detector upgrade. The reference
design represents a dramatic improvement over the initial complement of LIGO instruments. The
reference design is planned to lead to a quantum noise limited interferometer array with
considerably increased bandwidth and sensitivity.
The basic optical configuration is a power-recycled and signal-recycled Michelson interferometer
with Fabry-Perot “transducers” in the arms; see Figure 14. Using the initial LIGO design as a
point of departure, Advanced LIGO requires the addition of a signal-recycling mirror at the output
“dark” port, and changes in the RF modulation and control systems. This additional mirror allows
the gravitational wave induced sidebands to be stored in the arm cavities or extracted (depending
upon the state of “resonance” of the signal recycling cavity), and allows one to tailor the
interferometer response according to the character of a source (or specific frequency in the case
of a fixed-frequency source). For wideband tuning, “quantum noise” dominates the instrument
noise sensitivity at most frequencies (see Figure 15). Additional details may be found in Section
12. Interferometer Sensing and Controls Subsystem (ISC)38.
38
Please see http://www.ligo.caltech.edu/LIGO_web/docs/acronyms.html for a dictionary of acronyms
44
LIGO M030023-00M
SA PP HIR E,
4
SIL IC A,
35 C M 
KM
T =0.5%
A C TIV E
TH ER M AL
C OR R EC TION
MOD .
HE RA EU S SV
SIL IC A, IN ITIAL L IGO GR A DE
28.5CM 
INPUT MOD E
CLEAN ER
LASER
31.4 C M 40 K G 
ARM CAVITY
125 W
BS
PR M
T ~6%
830K W
ITM
SR M
POWER &
SIGNAL R EC YC LING
CAVIT IES
ETM
T=5%
OUT PUT MODE
CLEAN ER
PD
GW
R EAD OU T
Figure 14 Schematic of an Advanced LIGO interferometer, with representative mirror
reflectivities optimized for neutron star binary inspiral detection. Several new features
compared to initial LIGO are shown: more massive, sapphire test masses; 20  higher
input laser power; signal recycling; active correction of thermal lensing; an output mode
cleaner. (ETM = end test mass; ITM = input test mass; PRM = power recycling mirror;
SRM = signal recycling mirror; BS = 50/50 beam splitter; PD = photodetector; MOD =
phase modulation). Mode-matching and beam-coupling telescopes not shown.
The laser power is increased from 10 W to 100-200 W, chosen to be optimal for the desired
interferometer response, given the quantum limits and limits due to available optical materials.
The resulting circulating power in the arms is roughly 0.5 MW, in comparison with the initial LIGO
value of ~10 kW. The Nd:YAG pre-stabilized laser design resembles that of initial LIGO, but with
the addition of a more powerful output stage; see Section 8. Prestabilized Laser Subsystem
(PSL)). The conditioning of the laser light also follows initial LIGO closely, with a ring-cavity mode
cleaner and reflective mode-matching telescope, although changes to the modulators and
isolators must be made to accommodate the increase in power; see Section 9. Input Optics
Subsystem (IO)).
Whereas initial LIGO uses 25-cm diameter, 11-kg, fused-silica test masses, the test mass optics
for Advanced LIGO are larger in diameter (~32 cm) to reduce thermal noise contributions and
more massive (~-40 kg) to keep the radiation pressure noise to a level comparable to the
suspension thermal noise. Two materials are under study: sapphire and fused silica, and both
can be configured to lead to a satisfactory LIGO upgrade. The baseline choice for the core optics
substrate material is sapphire. Sapphire promises superior sensitivity for the measured material
parameters, and full-size samples are now under characterization. The beamsplitter and other
suspended optics, where thermal noise is less important, are made of fused silica. Polishing and
coating are not required to be significantly better than the best results seen for initial LIGO; see
Section 10. Core Optics Components (COC). Compensation of the thermal lensing in the test
mass optics (due to absorption in the substrate and coatings) is added to handle the much-
45
LIGO M030023-00M
increased circulating power – of the order of 1 MW in the arm cavities; see Section 11. Auxiliary
Optics Subsystem (AOS)
The test mass is suspended by fused silica ribbons or tapered fibers attached with hydroxycatalysis bonds, in contrast to the steel wire sling suspensions used in initial LIGO. Fused silica
has much lower loss (higher Q) than steel, and the fiber geometry allows more of the energy of
the pendulum to be stored in the earth’s gravitational field while maintaining the required strength,
thereby reducing suspension thermal noise. The resulting suspension thermal noise is anticipated
to be less than the radiation pressure noise and comparable to the Newtonian background
(“gravity gradient noise“) at 10 Hz. The complete suspension has four pendulum stages, and is
based on the suspension developed for the UK-German GEO-600 detector. The mechanical
control system relies on a hierarchy of actuators distributed between the seismic and suspension
systems to minimize required control authority on the test masses. The test mass magnetic
actuators used in the initial LIGO suspensions are eliminated (to reduce thermal noise and direct
magnetic field coupling from the permanent magnet attachments) in favor of electrostatic forces
for locking the interferometer and photon pressure for the operational mode. The much smaller
forces on the test masses reduce the likelihood of compromises in the thermal noise performance
and the risk of non-Gaussian noise. Local sensors (electrostatic and occultation) and
magnets/coils are used on the top suspension stage for damping, orientation, and control; see
Section 7. Suspension Subsystem (SUS).
The isolation system is built on the initial LIGO piers and support tubes but otherwise is a
complete replacement, required to bring the seismic cutoff frequency from ~40 Hz (initial LIGO) to
~10 Hz. RMS motions (dominated by frequencies less than 10 Hz) are reduced by active servo
techniques, and control inputs complement those in the suspensions in the gravitational-wave
band. The attenuation offered by the combination of the suspension and seismic isolation system
eliminates the seismic noise contribution to the performance of the instrument, and for the lowfrequency operation of the interferometer, the Newtonian background noise dominates. See
Section 6. Seismic Isolation Subsystem (SEI).
46
LIGO M030023-00M
Reference Design Parameters
The Advanced LIGO reference design is summarized in Table 1.
Table 1 Principal parameters of the Advanced LIGO reference design with initial LIGO
parameters provided for comparison
Subsystem and Parameters
Advanced LIGO
Reference
Design
Initial LIGO
Implementation
Observatory instrument lengths;
LHO = Hanford, LLO = Livingston
LHO: 4km, 4km;
LLO: 4km
LHO: 4km, 2km;
LLO; 2km
Strain Sensitivity [rms, 100 Hz band]
8×10-23
10-21
Displacement Sensitivity [rms, 100 Hz band]
8×10-20 m
4×10-18 m
Fabry-Perot Arm Length
4000 m
4000 m
Vacuum Level in Beam Tube, Vacuum
Chambers
<10-7 torr
<10-7 torr
Laser Wavelength
1064 nm
1064 nm
Optical Power at Laser Output
180 W
10 W
Optical Power at Interferometer Input
125 W
6W
Optical power on Test Masses
800 kW
30 kW
Input Mirror Transmission
0.5%
3%
End Mirror Transmission
15 ppm
15 ppm
Arm Cavity Power Beam size
6 cm
4 cm
Light Storage Time in Arms
5.0 ms
0.84 ms
Test Masses
Sapphire, 40 kg
Fused Silica, 11 kg
Mirror Diameter
32 cm
25 cm
Test Mass Pendulum Period
1 sec
1 sec
Seismic/Suspension Isolation System
3 stage active,
4 stage passive
Passive, 5 stage
Seismic/Suspension System Horizontal
Attenuation
10-12 (10 Hz)
10-9 (100 Hz)
Comparison With initial LIGO Top Level
Parameters
Reference Design Sensitivity Goal
The anticipated improvement in the performance of the reference design detector for wideband
tuning is indicated in Figure 14 (equivalent strain noise as a function of frequency). This
instrument is designed to deliver an improvement over initial LIGO in the rms noise and limiting
sensitivity by a factor of more than 10 over a very broad frequency band. This translates into an
increase of event rate by more than 1000 for extragalactic sources, so that several hours of
operation will exceed, in physics reach, the integrated observations of the 1-year initial-LIGO
47
LIGO M030023-00M
h(f)/Hz
1/2
Science Run. These Advanced LIGO interferometers will also have a greater frequency range
with both a reduced lower cutoff (10 Hz vs. 40 Hz) and a better high frequency performance (~8
times greater in frequency for comparable sensitivity). Finally, they will have the capability for a
reshaping of the noise curve. This allows e.g., narrowbanding with much enhanced sensitivity
near some chosen frequency as shown in Figure 15.
10
O
22
10
LIG
23
nts
adie
y gr
it
grav
Equivalent strain noise,
in
l
itia
24
10
1
10
Susp. thermal
Internal thermal
Quantum noise
Total noise
2
3
10
10
4
10
Frequency (Hz)
Figure 15 Noise Anatomy of Advanced LIGO. This model of the noise performance is
based on our current requirements set, and represents the principal contributors of the
noise and the least-squares sum of those components expressed as an equivalent
gravitational wave strain.
At the initial LIGO sensitivity, it is plausible but not probable that gravitational waves will be
detected. With Advanced LIGO it is probable to detect waves from a variety of sources and
extract rich information from them. Specifically (cf., Figure 16), Advanced LIGO is capable of the
following science:39

Inspiraling neutron star (NS) and black hole (BH) binaries: 1.4 MO• NS+NS binaries
will be detectable to a distance of 300 Mpc (estimated event rate ~2/yr to 3/day); 1.4 M O•
NS+10 MO• BH, detectable to 650 Mpc (estimated ~1/yr to 4/day); 10 M O• BH+BH,
detectable to redshift z=0.4 (estimated ~1/mo to 30/day – if black holes form in
completely symmetric events, then none will be seen, but this possibility is actually not
supported by current astronomical observations). The inspiral waves will reveal the
bodies’ masses and spins and will enable precision tests of general relativity at far higher
For details see, e.g., C. Cutler and K. Thorne, “An Overview of Gravitational-Wave Sources”,
http://xxx.lanl.gov/abs/gr-qc/0204090 and the many references cited therein.
39
48
LIGO M030023-00M






post-Newtonian order than is possible today [6 orders higher in (orbital speed) /(speed of
light).] New relativistic effects will be seen, e.g., radiation reaction due to tails of waves
and perhaps even tails of tails.
Tidal disruption of a NS by a BH: When the NS in a NS+BH binary nears its black-hole
companion, it can be torn apart by the hole’s spacetime curvature. The disruption waves
should carry information about the NS structure and equation of state. Extracting this
information will require three interferometers: two operating in wideband mode to
measure the inspiral waves and deduce from them the BH and NS masses and spins,
and one with noise curve optimized for the high-frequency (~300 to ~1000 Hz) disruption
waves. This 3-interferometer configuration can also seek NS equation-of-state
information by measuring the influence of tidal coupling on the wave spectrum from
inspiraling NS+NS binaries.
BH+BH mergers and ringdowns: When rapidly spinning BH’s collide, they should
trigger large-amplitude, nonlinear oscillations of curved spacetime around their merging
horizons. Little is known about the dynamics of spacetime under these extreme
circumstances; we can learn about it by comparing LIGO’s observations of the emitted
waves with supercomputer simulations. Advanced LIGO can detect the merger waves
from BH binaries with total mass as great as 2000 MO
• , to cosmological redshifts as large
as z=2.
Supernovae: Empirical evidence suggests that neutron stars in type II supernovae
receive kicks of magnitude as large as ~1000 km/s. These violent recoils imply the
supernova’s collapsing-core trigger may be strongly asymmetric, emitting waves that
might be detectable out to the Virgo cluster of galaxies (event rate a few/yr) and perhaps
beyond. Even when the collapse is spherical and emits no waves, the collapsed core
(proto-neutron star) is predicted to be unstable to convective overturn. The gravitational
waves from this convection may be detectable throughout our Galaxy and its orbiting
companions, the Magellanic Clouds. By cross correlating the gravitational waves with
neutrinos from just one such (very rare) event, we could learn much about the protoneutron star’s convecting core.
Gamma-ray bursts: The triggers of gamma ray bursts are thought to be the collapse of
massive stellar cores (hypernovae) and/or the merger of NS+NS or NS+BH binaries, all
of which emit strong gravitational waves. The next generation of orbiting gamma-ray
telescopes will be operational in the time frame of Advanced LIGO, providing
astrophysical triggers for LIGO’s searches. With the aid of these triggers, and with
predicted enhancements of the gravitational waves along the burst’s beaming direction
(toward earth), estimates suggest coincident detections of a few per year. Any such
detection would reveal the nature of the gamma-burst trigger. The third interferometer,
with noise curve reshaped for better sensitivity at high frequencies, may enable
observations of the trigger’s dynamics.
Spinning neutron stars: The narrowband tunability of the third interferometer will be
exploited to search with high sensitivity at high frequencies for gravitational radiation
arising from spinning NS’s: known pulsars and Low-Mass X-Ray Binaries (LMXB’s), and
unknown pulsars. If (as is plausible) a NS’s accretion torque, in an LMXB, is
counterbalanced by its gravitational radiation-reaction torque, then its wave strength is
predictable from the observed X-ray flux, and about 10 known LMXB’s would be
detectable by Advanced LIGO with narrow-banding (the dots near the minimum of the
narrow-band curve) but only one (Sco X-1, the star in Figure 16) without narrow-banding.
These LMXB’s may serve as “calibration sources” for LIGO. A NS’s crustal shear or
internal magnetic field is predicted to be able to support non-axisymmetric ellipticities as
large as ~-6 or even 10-5. A narrowbanded interferometer could detect a known
millisecond pulsar with  as small as 2x10-8(1000Hz/f)2(r/10kpc), where f is the wave
frequency (most likely twice the spin frequency) and r is the distance. In an all-sky, allfrequency search the sensitivity would be degraded by a factor of a few to ~15.
Stochastic Waves: The sensitivity improvement of Advanced LIGO, coupled with the
decrease in lower frequency cutoff, means that an observational measurement of the
49
LIGO M030023-00M

stochastic gravitational wave background can be performed with a sensitivity after 1 year
of observation of GW~5x10-9 (GW is the ratio of the stochastic gravity-wave energy
density contained in a bandwidth ∆f = f to the total energy density required to close the
universe; a flat spectrum is assumed).The sources of such background in the LIGO band
are all highly speculative and could be weaker than 5x10-9 if they exist at all, but also
might be stronger and detectable. Some examples can be given: cosmic strings and
other topological defects in the structure of spacetime, first-order phase transitions in the
states of quantum fields at temperature ~109 K in the very early universe, Goldstone
modes of scalar fields that arise in supersymmetric and string theories, coherent
excitations of our 3+1 dimensional universe, regarded as a brane in a higher dimensional
universe, and the birth of the universe as described by string-motivated “pre-big-bang”
cosmology.
The Unexpected: We are very ignorant of the gravitational universe, and it seems quite
probable that Advanced LIGO’s observations will bring some significant surprises.
Figure 16 The estimated signal strengths hs(f) from various sources (thin lines, filled
circles and star) compared with the noise h(f) (heavy lines) of three interferometers:
initial LIGO, Advanced LIGO in a wideband (WB) mode, and Advanced LIGO
narrowbanded (NB) at 600 Hz. See text for explanations of sources. The signal strength
hs(f) is defined in such a way that, wherever a signal point or curve lies above the
interferometer's noise curve, the signal, coming from a random direction on the sky and
with a random orientation, is detectable with a false alarm probability of less than one
per cent using currently understood data analysis algorithms.
Reference Design Options and Selection
The Advanced LIGO reference design has as its baseline that all three LIGO interferometers will
be upgraded as described. It assumes, furthermore, that the upgrades will produce identical
interferometers, though they may be run with different detailed parameters such as output laser
50
LIGO M030023-00M
power and different signal tuning and signal-recycling mirror transmission. The principal options
for the reference design are described below.
Number of Upgraded Interferometers
The upgrade could be restricted to a single interferometer at each LIGO site. The Hanford 2kilometer interferometer could be retained in its present configuration or decommissioned.
However, in the discovery phase of LIGO observations, prior to confirmed observation of
gravitational waves, the third interferometer may provide additional confidence and an increase of
the volume of the universe that LIGO can see by as much as 50%; in the phase after initial
detections, an additional interferometer could be tuned and used in combination with the other
LIGO instruments and with other networked detectors to significant astrophysical advantage. If
the upgrade of the third interferometer is dropped from the scope of the Advanced LIGO project, it
will reduce the costs and required resources.
2-Kilometer Interferometer Upgraded but Not Converted to 4 Kilometer Length
This option could be employed if it is felt that a half-size gravitational wave signal is useful in
separating genuine signals and that retaining this feature outweighs the advantages of increasing
sensitivity that accompanies an increase in arm length. At this time, the improved sensitivity of the
longer interferometer is compelling, and we choose to increase the arm cavity length in the
reference design. If extending the arm cavity is dropped from the scope of this upgrade, the costs
and resources required will be modestly reduced from those required in the baseline design.
Simultaneous Implementation of the Upgrade
Our baseline plan calls for a staged implementation of the upgrade, in which the Livingston
instrument installation is started first, with the installation at Hanford to follow by 8 months. This
distributes both fabrication and installation demands over a reasonable period. An alternative
would be to engage in a simultaneous installation at the two observatories. This would stress the
manpower and the facilities, and would require some duplication of installation equipment. It
would potentially reduce the duration during which the pair of LIGO observatories is “off-line.”
Simultaneous implementation may increase the costs, resources and schedule required to
complete the Advanced LIGO upgrade.
Test Mass Substrate Material
Sapphire is selected as the substrate material in this reference design. It offers significant
advantages in reducing thermal noise and in control of thermal distortions on the optics. It
requires greater development and carries greater risk than fused silica in crystal growth, cost,
optical performance, polishing and coating. Our program will carry fused silica as a fallback
option, with some impact on the detector sensitivity, with a well-defined date for confirmation of
sapphire or adoption of fused silica for the baseline. If sapphire is dropped from the baseline
reference design, the costs, schedule and resources required for Advanced LIGO will likely be
unchanged.
Future Incremental Upgrades to Advanced LIGO
The Reference Design balances technical challenges and improved performance. The stability of
the design through the intensive R&D effort to date has demonstrated its robustness. The design
is, however, flexible and can accommodate all foreseeable improvements to this type of detector;
51
LIGO M030023-00M
a room-temperature, transmissive-optic, Fabry-Perot Michelson. Some examples that have been
explored are as follows:




Quantum non-demolition techniques: The baseline sensing system experiences the
stored light as an “optical spring” which helps to reduce the quantum noise below the
naïve limit. Modifications to the interferometer’s input and/or output port fields may allow
further reduction of quantum noise.
Newtonian background cancellation: The changes in mass distribution near the test
masses (primarily due to seismic noise) appear as a low-frequency noise limit. Monitoring
this motion with an array of seismometers may allow a regression or cancellation to
observe at lower frequencies.
Non-Gaussian laser light profiles: The thermal motion of the mirror surface, especially for
the thermoelastic noise which dominates in the case of sapphire, has a smaller net effect
for larger light beams. Introduction of slightly non-spherical end test masses would lead
to non-Hermite-Gaussian modes with a larger waist that could reduce this noise source,
giving better sensitivity at intermediate frequencies.
Variable reflectivity signal recycling mirror: The tunability of the interferometer response is
limited with a fixed transmission signal-recycling mirror. Forming a low-finesse outputcoupling cavity from a substrate coated on both sides could allow a thermally tuned
output coupler, giving a broader range of instrument response functions.
These options may be proposed after observation with the present baseline design for Advanced
LIGO. Some may be able to be incorporated into the design shortly after, or coincident with, the
commissioning of the baseline. For example, the variable reflectivity signal-recycling mirror has
been proposed as an Advanced LIGO enhancement from the Australian consortium ACIGA (see
next section).
52
LIGO M030023-00M
3. Program Plan
LIGO Laboratory Role and Responsibilities
Scientists, engineers, and staff at the California Institute of Technology (Caltech) and the
Massachusetts Institute of Technology (MIT) carry out the design, construction, and operation of
the LIGO Observatories. Caltech has prime responsibility for the project under the terms of a
Cooperative Agreement40 with the National Science Foundation (NSF). LIGO is a national facility
for gravitational-wave research, providing opportunities for the broader scientific community to
participate in detector development, observations and data analysis. Under the Cooperative
Agreement, the LIGO Laboratory assumes responsibility for implementation of the Advanced
LIGO upgrade project.
Figure 17 illustrates the reporting relationship between the LIGO Laboratory and the managing
institutions, NSF, Caltech and MIT.
NSF
National Science Board
Director of NSF
Mathematical and
Physical Sciences
Budget and Finances
Physics
Division of Grants
and Agreements
Cooperative
Agreement
LIGO Program
Management
MIT
CALTECH
President
Memorandum
of
President
Understanding
Legal Counsel
Provost
LIGO
Oversight
Committee
CIT/MIT
Dean of Science
Center for Space
Research
Physics
Provost
VP Business
and Finance
Physics Mathematics
and Astronomy
Office of Sponsored
Research
LIGO Laboratory
MIT LIGO
CIT LIGO
Figure 17 LIGO Laboratory Reporting and Oversight
The LIGO Laboratory will manage Advanced LIGO construction in the same manner as the
original LIGO construction was executed. A project organization will be established within the
LIGO Laboratory with a Work Breakdown Structure (WBS) defining the tasks leading to project
deliverables. The project organization will parallel the deliverables in the WBS. Task Leaders for
40
Cooperative Agreement PHY-0107417 between the National Science Foundation, Washington, D.C.
20550 and the California Institute of Technology, Pasadena, CA 91125; LIGO Construction was
performed under Cooperative Agreement PHY-9210038.
53
LIGO M030023-00M
each organizational element will be charged with delivering the elements of Advanced LIGO.
Prior to initiating the Advanced LIGO project, an Advanced LIGO Project Management Plan will
define the details of this organization. Advanced LIGO construction will be a broad effort of the
LIGO Scientific Collaboration (LSC), and the WBS and organization chart will reflect the
collaborative distribution of the responsibilities.
LIGO Scientific Collaboration Role and Responsibilities
Collaborating groups have established the LSC to carry out the LIGO research and development
program, to develop priorities, and to enable participation. It is organized as a separate entity
distinct from the LIGO Laboratory. Through its Spokesperson, the LSC communicates with the
Laboratory through the Laboratory Directorate.
Collaborative work between the LIGO Laboratory and the LIGO Scientific Collaboration is defined
in Memoranda of Understanding (MOU)41 between the Laboratory and responsible institutions.
Specific tasks are included in Attachments to these MOUs with defined deliverables and periods
of performance. A specific MOU and Attachment define membership by an institution in the LSC.
Fulfillment of the commitments made by both parties to Attachments is reviewed by periodic
progress reports and by revision of the Attachments to define future commitments.
Member institutions in the LSC participate in the research and development program leading to
enhanced LIGO detectors. These activities are defined in MOUs and Attachments, and, where
applicable, through awards from the NSF.
Participation by member LSC institutions in the execution of the Advanced LIGO construction
project is possible and encouraged. Such participation will be governed by specific Attachments
defining each institution’s roles and contributions to the Advanced LIGO project. This
management technique has been used successfully in the execution of initial LIGO construction.
Participant institutions may receive needed funding through subcontracts with the LIGO
Laboratory or through funding from other agencies or foreign sources depending upon the
particular role and situation of each institution. The NSF is fully involved in reviewing and
approving participation by non-NSF supported institutions.
This Project Book represents the definition of the Advanced LIGO project as jointly defined by the
LIGO Laboratory and the LSC.
International Collaboration in Advanced LIGO
A major role in Advanced LIGO R&D, construction and implementation is proposed for the GEO
Project42, a collaboration of United Kingdom and German institutions. The GEO Project has
carried out extensive research and development of technologies fundamental to the Advanced
LIGO design. They have designed and are commissioning a 600-meter interferometer that will
serve, in addition to its intrinsic goals as a gravitational wave detector, as a test bed for Advanced
LIGO techniques. They are carrying out important research in suspension of core optics, in
reduction of thermal noise, in relevant materials processing, in modeling of instrument
performance and sensitivity, in data acquisition and analysis, and in advanced interferometer
configurations. Much of this work is directly relevant to defining the Advanced LIGO detector
system.
The GEO institutions will lead the definition, design and construction of the suspensions for the
Advanced LIGO test mass optics. Based upon the GEO-600 multiple pendulum suspensions, the
Advanced LIGO version makes a pivotal contribution to the performance enhancement of LIGO.
41
42
http://www.ligo.org/mou/mou.html
http://www.geo600.uni-hannover.de/
54
LIGO M030023-00M
Similarly, the GEO work in signal tuned interferometer configurations underpins the Advanced
LIGO design and performance goal and GEO is undertaking a continuing role in this area. GEO is
assuming responsibility to develop and construct the Advanced LIGO Prestabilized Laser
systems. GEO has proposed direct support of the Advanced LIGO project to the United Kingdom
funding agencies, and plans a request to the German funding agencies 43. The GEO role in
executing and participating in the management of the project will be defined through the bilateral
MOU and Attachment process described here.
A significant role in Advanced LIGO R&D, construction and implementation is also proposed by
the Australian Consortium for Interferometric Gravitational Astronomy44 (ACIGA). ACIGA has an
active R&D program on Advanced LIGO techniques including research on the design and
development of a 100 W class laser and optical systems compatible with those power levels,
control systems for advanced interferometer configurations, and data analysis. ACIGA is
constructing a facility at its Gingin site to test the performance of optical systems subjected to
high power, a crucial experimental analysis of one of the key Advanced LIGO concepts.
Furthermore, ACIGA proposes to expand the capability of Advanced LIGO by leading the
development of a variable reflectivity signal recycling mirror, which will allow in-situ manipulation
of the instrument’s bandwidth. ACIGA is proposing direct support of the Advanced LIGO project
to the Australian Research Council that would support the R&D on variable-reflectivity mirrors,
and also contribute to the baseline output optics subsystem of Advanced LIGO. It has already
been funded for the test facility construction.
Method of Accomplishment
Advanced LIGO is an effort of the entire LIGO Scientific Collaboration. The LIGO Laboratory will
manage the project with oversight of all participating institutions. This management will be defined
in the MOUs and Attachments for participating institutions outside the LIGO Laboratory. Within
the Laboratory, tasks will be assigned to designated Task Leaders and assigned staff reporting to
these Task Leaders. Task leaders may come from the greater LIGO Scientific Collaboration,
working with a liaison within the Laboratory.
For each component, supply or service required for Advanced LIGO, the Laboratory will employ
either an in-house fabrication or provision of the item or service, or will procure the item or service
through a subcontract. It is expected that a substantial fraction of the Advanced LIGO system
components will be procured through subcontracts based upon the Advanced LIGO project
specifications. The Laboratory and scientific partners will primarily carry out design, contractor
supervision, receipt, testing, acceptance, final assembly, installation, integration and
commissioning. Formal management of subcontracts will in general be the responsibility of the
LIGO Laboratory under the terms of the Cooperative Agreement, though international partners
will carry out some subcontracting directly.
43
Exploring the Dark Side of the Universe: Proposal for UK Involvement in Advanced LIGO,
available at http://www.physics.gla.ac.uk/gwg/AdvLIGO%20Proposal%20Web%20Version.pdf
44 http://www.anu.edu.au/Physics/ACIGA/
55
LIGO M030023-00M
4. Work Breakdown Structure (WBS)
The LIGO Work Breakdown Structure prior to Advanced LIGO construction is:
1.0 Initial LIGO Construction
2.0 LIGO Laboratory Operations
3.0 LIGO Laboratory Advanced R&D
For Advanced LIGO construction, we establish a new top-level WBS designation:
4.0 Advanced LIGO Project
The definitions of the Advanced LIGO first and second level WBS elements are:
4.0. Advanced LIGO Project (Advanced LIGO)
This element includes all costs for removal and securing initial LIGO systems, R&D and design,
prototype testing, fabrication of items for the upgrade, and all materials and labor necessary to
bring the system to completion of the installation phase. It does not include the labor for the final
commissioning or for the operational phase.
4.1. Facility Modifications (FAC)
This element includes modifications and additions to buildings, vacuum systems, and permanent
fixed infrastructure that are needed to support the Advanced LIGO detectors. It does not include
other facility additions or modifications carried out as normal operations or maintenance tasks.
4.2. Seismic Isolation Subsystem (SEI)
This element includes all R&D, design, prototype testing, and hardware for the seismic isolation
system upgrade. It includes all components of active elements including programmable controls
items, and software specific to local control of this subsystem. It does not include general controls
for the interferometer, nor shared controls infrastructure.
4.3. Suspension Subsystem (SUS)
This element includes all R&D, design, prototype testing, and hardware for the suspension
subsystem upgrade, including suspension fibers and attachment to the core optics. It includes the
intermediate masses. This element provides small suspensions mechanical hardware for other
subsystems. It includes all physical hardware for sensing and control (including the electrostatic
actuator, but not the photon actuator) of suspended masses. It includes all components of active
elements including programmable controls items, and software specific to local control of this
subsystem. It does not include general controls for the interferometer, nor shared controls
infrastructure. It does not include controls hardware and software specific to other subsystems for
which the mechanical suspensions are supplied by this element.
56
LIGO M030023-00M
4.4 Prestabilized Laser Subsystem (PSL)
This element includes all R&D, design, prototype testing, and hardware for the pre-stabilized
laser subsystem upgrade (one operational and one spare per interferometer, and two prototypes).
It includes all components of active elements including programmable controls items, and
software specific to local control of this subsystem. It includes the final intensity stabilization
system. It does not include general controls for the interferometer, nor shared controls
infrastructure.
4.5. Input Optics Subsystem (IO)
This element includes all R&D, design, prototype testing, and hardware for the input optics
subsystem upgrade. Suspension mechanical hardware is provided by the suspension subsystem,
and controls are provided by the interferometer sensing and controls subsystem. It includes all
other components of active elements including programmable controls items, and software
specific to local control of this subsystem. It does not include the shared controls infrastructure.
4.6. Core Optics Components (COC)
This element includes all R&D, design, prototype testing, design, purchase of materials, polishing,
coating, metrology, cleaning and preparation and transport of the core optics and spares. It
includes preparations of the optic for installation in the suspension, but it does not include
physical elements attached to the optics required for suspension fiber attachment.
4.7. Auxiliary Optics Subsystem (AOS)
This element includes all R&D, design, prototype testing, and hardware of the output optics
subsystem (OO) (all telescopes, output mode cleaner, and miscellaneous steering optics), the
stray light control (SLC) subsystem (beam dumps and baffles), the photon actuator for the test
mass suspensions (PHO), and the active optics thermal compensation subsystem (AOC).
Controls are designed by the interferometer sensing and controls subsystem.
4.8. Interferometer Sensing and Controls Subsystem (ISC)
This element includes all R&D, design, prototype testing, and hardware for the sensing, signal
conditioning and digital conversion electronics, programmable items, computers, and software for
the servocontrol of the Advanced LIGO interferometer systems. These include control and
coordination of all degrees of freedom of the interferometer up to the interface points with the
PSL, AOS, SUS, and SEI subsystems, and sensing and readout of lengths and angles of optical
elements.
4.9. Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ)
This element includes all R&D, design, prototype testing, and hardware for the analog and digital
signal conditioning electronics, computers, programmable items, networking, software, sensors,
actuators and excitation devices for reading Advanced LIGO data and diagnostic data and
operating diagnostic systems. Common elements of the supervisory control and human interface
for subsystems, and the infrastructure (cable plant, servers, etc.) are also in this subsystem. The
element includes all additions and modifications to the LIGO Global Diagnostics System (GDS)
and the Physics Environmental Monitor (PEM) system.
4.10. Support Equipment (SUP)
This element includes support equipment additions and upgrades needed to install, operate and
maintain the Advanced LIGO systems. This element represents equipment, interface systems
and support infrastructure that is not subsystem specific.
57
LIGO M030023-00M
4.11. Advanced LIGO Construction Project Research and Development (R&D)
This element includes those R&D activities required to specifically address Advanced LIGO
implementation in addition to that planned per subsystem. It is reserved for R&D tasks identified
during the fabrication phase and early installation and commissioning. It does not include any
tasks included within the LIGO Advanced R&D program currently supported by the NSF and
related to Advanced LIGO nor any R&D activities normally carried out within the LIGO Laboratory
operations program (WBS 2.0). There are currently no activities in this WBS.
4.12. Data Analysis and Computing Subsystem (COMP)
This element includes all incremental upgrades to data analysis systems and computational
infrastructure needed to support the analysis of data from Advanced LIGO. It includes neither
software nor computing nor network hardware supported normally by the LIGO Laboratory
operations program (WBS 2.0). It does include the LIGO Data Analysis System (LDAS) and the
End-to-End Model (E2E) infrastructure development.
4.13. Installation and Commissioning Task (INS)
This element includes all support for the installation and subsystem commissioning of Advanced
LIGO. It also includes all effort to remove and preserve all components of the initial LIGO
subsystems not employed in Advanced LIGO.
4.14. Project Management (PM)
This element includes all costs of management of the Advanced LIGO construction incremental to
the support provided by the LIGO Operations budget (WBS 2.0). These costs will support cost
estimating, scheduling, performance definition and measurement, acquisition, quality assurance,
ES&H, document control, review and consultation, and system engineering.
58
LIGO M030023-00M
5. Facility Modifications (FAC)
Overview
Advanced LIGO technical requirements will necessitate modifications and upgrades to the LIGO
buildings, and vacuum equipment. In addition, the strategy for executing the Advanced LIGO
construction will require some facility accommodations.
The principal impact on this WBS element is as follows:



It is a program goal to minimize the period during which LIGO is not operating
interferometers for science. For this reason, major subsystems such as the seismic
isolation and suspension subsystems should be fully assembled and staged in locations
on the LIGO sites ready for installation into the vacuum system as fully assembled and
vacuum compatible units. This will require prepared assembly and staging space,
materials handling equipment, and softwall clean rooms.
Increasing the arm cavity length for the Hanford 2-kilometer interferometer to 4 kilometers
will require removing and reinstalling the existing mid-station chambers and replacing
them with spool pieces in the original locations. An alternate strategy would be to
fabricate additional vacuum tanks for the end stations, and associated spool pieces and
preparation. Moving the existing chambers is the choice for the baseline design.
The larger optical beams in the input optics section (and possibly the output optics
section) will necessitate changing out the input optics vacuum tube for a larger diameter
tube.
Functional Requirements
Vacuum Equipment
All vacuum equipment functional requirements are the same as those in the initial LIGO design
except that the vacuum level must be one order of magnitude lower (<10-7 torr). Additional
equipment (chambers, spool pieces, softwall clean rooms) is needed to accommodate additional
arm cavity length for one interferometer and the desire for parallel assembly and installation in
more chambers and staging areas. A larger diameter spool piece for the IO Mode Cleaner beam
path (and possibly for a similar output mode cleaner) is required. The seismic isolation system
requirements45 call for the Advanced LIGO subsystems to be compatible with the original LIGO
vacuum envelope.
Beam Tube
The original end-pumped beam tube system requires no modifications or additions for Advanced
LIGO. There is sufficient margin in the present vacuum performance to permit the operation of the
more sensitive Advanced LIGO instrument with no changes.
Conventional Facilities
Preassembly of all large Advanced LIGO seismic isolation units prior to installation in the vacuum
tanks requires clean onsite staging and assembly space. At both the Hanford and Livingston
Observatories there exist suitable staging buildings with appropriate height and basic
45
LIGO-II Seismic Isolation Design Requirements Document, LIGO-E990303-03-D
59
LIGO M030023-00M
configuration; portable clean rooms and benches are required. Transporters for delivering fragile
systems from the central buildings to the end stations are required.
Concept/Options
Vacuum Equipment
Two softwall cleanrooms of the BSC type will be acquired for seismic assembly in the Hanford
staging building. Two will be required for Livingston. For each of the interferometers, additional
clean rooms will be acquired to support parallel installation in additional chambers to facilitate
reducing the duration of Advanced LIGO installation.
Four additional spool pieces will be acquired to replace the Hanford mid-station BSC chambers
and to connect these chambers to the end-station BSC chambers once relocated. The chambers
will be removed and reinstalled at the end stations. An alternative approach involves acquiring
new BSC chambers and leaving the original chambers in place. Vacuum controls will be added at
the end stations to accommodate the BSC chambers in their new location.
The IO (and potentially the output) Mode Cleaner requires a larger diameter spool piece, ~15m in
length, to accommodate the larger mirrors used.
The requirement of base pressure for Adv LIGO (<10-7 torr) is already met by the present system
(which is operating at <10-8 torr).
Beam Tube
No action needed. The original installation meets requirements for Advanced LIGO.
Conventional Facilities
The existing staging buildings at both observatories will require additions of flow benches, fume
hoods, vacuum bake ovens, and other minor equipment to support clean processing operations.
In addition, at LHO some retrofit of the HVAC system will be necessary in the Staging Building to
meet the cleanliness requirements. HEPA filters and a more powerful motor are needed.
R&D Status/Development Issues
There are no development issues or R&D associated with this WBS element.
Work Plan
Long lead procurements dominate this schedule sensitive WBS element. With funding assumed
to commence in FY2005, contracts can be placed promptly for the softwall clean rooms and flow
benches. These must be in place prior to commencement of seismic assembly by mid 2006.
Procurement of vacuum equipment for conversion of the Hanford 2-kilometer interferometer
should commence in 2006.
60
LIGO M030023-00M
6. Seismic Isolation Subsystem (SEI)
Overview
The seismic isolation subsystem serves to attenuate ground motion in the observation band
(above 10 Hz) and also to reduce the motion in the “control band” (frequencies less than 10 Hz).
It also provides the capability to align and position the load. Significantly improved seismic
isolation will be required for Advanced LIGO to realize the benefit from the reduction in thermal
noise due to improvements in the suspension system. The isolation system will be completely
replaced, and this offers the opportunity to make a coordinated design including both the controls
and the isolation aspects of the interferometer.
Functional Requirements
The top-level constraints on the design of the isolation system can be summarized:




Seismic attenuation: The amplitude of the seismic noise at the test mass must be equal
to or less than the thermal noise of the system (10-19 m/Hz at 10 Hz) for the lowest
frequencies where observation is planned. We have chosen 10 Hz as, at this frequency,
the competing noise sources (suspension thermal noise, radiation pressure, Newtonian
background) all conspire to establish a presently irreducible sensitivity level roughly a
factor of 30 above the limits imposed by the LIGO facilities, and because technical
difficulties in suspension design make a lower goal unrealistic.
The RMS differential motion of the test masses while the interferometer is locked must
be held to a small value (less than 10-14 m) for many reasons: to limit light fluctuations at
the antisymmetric port and to limit cross coupling from laser noise sources, as examples.
Similarly, the RMS velocity of the test mass must be small enough and the test mass
control robust enough that the interferometer can acquire lock. This establishes the
requirement on the design of the seismic isolation system in the frequency band from 0.1
to 10 Hz.
The isolation positioning system must have a large enough control range to allow the
interferometer to remain locked for extended periods; our working value is 1 week.
The system must interface with the rest of the LIGO system, including LIGO vacuum
equipment, the adopted suspension design, and system demands on optical layout and
control.
A more complete reference on Advanced LIGO seismic isolation requirements is available 46.
Concept
The initial LIGO seismic isolation stack will be replaced with an external (to the vacuum) lowfrequency pre-isolator stage, and an in-vacuum two-stage active seismic isolation platform
(Figure 18 is taken from the design model). The in-vacuum stages are mechanically connected
with stiff springs, yielding typical passive resonances in the 2-8 Hz range. Sensing its motion in 6
degrees of freedom and applying forces in feedback loops to reduce the sensed motion
attenuates vibration in each of the two-cascaded stages. The outer stage derives its feedback
signal by blending three real sensors for each degree of freedom: a long-period broadband
seismometer, a short-period geophone, and a relative position sensor. The inertial sensors
(seismometers and geophones) measure the platform's motion with respect to their internal
suspended test masses. The position sensor measures displacement with respect to the adjacent
stage. The resulting “super-sensor” has adequate signal-to-noise and a simple, resonance-free
46
LIGO-II Seismic Isolation Design Requirements Document, LIGO-E990303-03-D
61
LIGO M030023-00M
response from DC to several hundred Hz. The inner stage uses the position sensor and highsensitivity geophone, and some feed-forward from the outer stage seismometer.
Figure 18 Computer rendering of the conceptual design of the two-stage active isolation
system for the test-mass (BSC) vacuum chambers. The outside frame supports the first
stage from three trapezoidal blade springs. Three plug-in units carry the sensors and
actuators for the unit. The inner second stage is likewise suspended from trapezoidal
springs, with the sensor/actuators protruding above the upper surface. The optics are
suspended below the inner stage (which forms the interface to the suspension and other
isolated parts), and hang below the support structure (HPD).
The outer frame of the isolation system is designed to interface to the existing in-vacuum seismic
isolation support system, simplifying the effort required to exchange the present system for the
new system. The outer stage is hung from the outer frame using trapezoidal leaf springs to obtain
the 2-6 Hz resonances. The inner platform stage is built around a 1.5-m diameter optics table
(BSC) or a larger polygonal table (HAM). The mechanical structures are carefully studied to bring
the first flexible-body modes well above the ~50 Hz unity gain frequencies of the servo systems.
For each suspended optic, the suspension and auxiliary optics (baffles, relay mirrors, etc.) are
mounted on an optical table with a regular bolt-hole pattern for flexibility.
We will use commercial, off-the-shelf seismometers that are encapsulated in a removable pod.
This allows the sensors to be used as delivered, without concerns for vacuum contamination, and
allows a simple exchange if difficulties arise. The actuators consist of permanent magnets and
coils in a configuration that encloses the flux to reduce stray fields. These components must meet
the stringent LIGO contamination requirements. The multiple-input multiple-output servo control
system is realized using digital techniques; 16-bit accuracy with ~2 kHz digitization is sufficient.
62
LIGO M030023-00M
The external pre-isolator is used to position the in-vacuum assembly, with a dynamic range of 1
mm, and with a bandwidth of 2 Hz or greater in all six degrees of freedom. This allows
feedforward correction of low-frequency ground noise and sufficient dynamic range for Earth tides
and thermal or seasonal drifts. We target approximately a factor of 10 reduction of the ~0.16 Hz
microseismic motion from feedforward correction in this stage. For corrections up to the 1-cm
clearance at each vacuum feedthrough bellows, large screw adjustments are included in series
with each external actuator.
The performance of the system, and its initial design, is calculated with a model that includes all
solid-body degrees of freedom, and measured or published sensitivity curves (noise and
bandwidth) for sensors. It meets the Advanced LIGO requirements with some margin, for both the
test-mass (BSC) and auxiliary (HAM) chambers.
The passive isolation of the suspension system provides the final filtering. A sketch of the system
as applied to the test-mass vacuum chambers (BSC) is shown in Figure 19; a similar system is
designed for the auxiliary optics chambers (HAM). Further details can be found in the subsystem
Design Requirements and Conceptual Design documents47.
Figure 19 Rendering of isolation system installed in the BSC (Test Mass Chambers),
with suspension system attached below. The external preisolator provides the interface
between the vertical blue piers and the green horizontal support structure (C. Hardham,
Stanford).
47
Advanced LIGO Seismic Isolation System Conceptual Design, E010016-00
63
LIGO M030023-00M
R&D Status/Development Issues
A first-generation prototype48 of the in-vacuum isolation system has shown performance at lowand high-frequencies comparable to the requirements. Testing of a preliminary version of the
external pre-isolator49 is nearing completion and will be installed in Livingston in 2003 as a
remedial effort addressing excess local seismic noise. Testing started in December 2002 on a
second-generation prototype of the in-vacuum isolation at the Stanford Engineering Test
Facility50.
Several issues must be addressed. The most significant is identifying the character of the internal
mechanical resonances of as-built designs and crafting control laws that meet requirements in
this environment. Other issues include minimizing the confusion of tilt with horizontal motion for
low-frequency control, the distribution of control authority through the hierarchy, and stability of
parameters (for feed-forward and loop gain design). In addition, processors, analog interfaces,
and software systems that are compatible with the LIGO standard will be integrated into the
subsystem.
Materials issues requiring study include the development of contamination-compatible in-vacuum
electromagnetic actuators, and creep and yield behavior of structural materials under stress.
Work Plan
The present LIGO Cooperative Agreement and existing NSF grants to LSC member institutions
will support research, development, and design on this subsystem through full-scale tests carried
out in the MIT LASTI testbed. These involve control and noise-performance tests of complete
systems for both the test-mass and the auxiliary optics vacuum chambers, as well as their
integration with the suspensions (SUS).
Advanced LIGO construction will commence with a final design review and with placement of
production subcontracts for all seismic subsystem components. Fabricated components must
begin arriving at the staging buildings at the two sites in early 2006.
Assembly of complete seismic system units in the staging buildings will take place during 2006.
Sufficient systems must be completed at both sites to support installation in the interferometer
vacuum chambers in mid-2006.
48
R. Abbott, R. Adhikari, G. Allen, S. Cowley, E. Daw, D. DeBra, J. Giaime, G. Hammond,
M. Hammond, C. Hardham, J. How, W. Hua, W. Johnson, B. Lantz, K. Mason, R. Mittleman,
J. Nichol, S. Richman, J. Rollins, D. Shoemaker, G. Stapfer, and R. Stebbins. Seismic isolation
for advanced LIGO. Classical and Quantum Gravity 19(7):1591, 2002. P010027-01-R
49 Initial LIGO Seismic Isolation Upgrade Design Requirements Document, T020033-02-D
50 http://www.ligo.caltech.edu/docs/G/G010193-00.pdf
64
LIGO M030023-00M
7. Suspension Subsystem (SUS)
Overview
The test-mass suspension subsystem must preserve the low intrinsic mechanical losses (and
thus the low thermal noise) in the fused silica suspension fibers and sapphire test mass material.
It must provide actuators for length and angular alignment, and attenuate seismic noise. The
Advanced LIGO reference design suspension is similar in design to the GEO 600 multiple
pendulum suspensions, with requirements to achieve a seismic wall of ~10 Hz. A variety of
suspension designs are needed for the main interferometer and input conditioning optics.
Functional Requirements
The suspension forms the interface between the seismic isolation and the suspended optics. It
provides seismic isolation and the means to control the orientation and position of the optic.
These functions are served while minimally compromising the thermal noise contribution from the
test mass mirrors and only introducing a negligible amount of thermal noise from the suspension
elements.
The optic (which in the case of the main arm cavity mirror serves also as the test mass) is
attached to the suspension fiber during the suspension assembly process and becomes part of
the suspension assembly. Features on the test mass will be required for attachment and
potentially for actuation. The test mass suspension system is mounted (via bolts and/or clamps)
to the seismic isolation system by attachment to the SEI optics table.
Local signals are generated and fed to actuators to damp solid body motions of the suspension
components; in addition, control signals generated by the interferometer sensing/control (ISC) are
received and turned into forces on the test mass to obtain and maintain the operational lengths
and angular orientation. There are two variants of the test mass suspension: one for the End Test
Mass (ETM) which carries potentially non-transmissive actuators behind the optic, and one for the
Input Test Mass (ITM) which must leave the input beam free to couple into the Fabry-Perot arm
cavity. There are also variants for the beamsplitter, folding mirror, and recycling mirrors; and for
the mode cleaner, input matching telescope, and suspended steering mirrors.
A multiple-pendulum is the basis. This has two benefits:


it provides a mechanical filter to reduce noise injected by the controllers and the thermal
noise of the lower Q isolation stages above,
it enables a considerable reduction of control forces exerted on the test mass itself.
The latter feature will allow the elimination of the magnets attached to the test mass in initial LIGO
(which are the largest source of excess dissipation on the test mass), and should allow the test
mass to reach a mechanical loss (and thus thermal noise) limited principally by the substrate
material. Furthermore, eliminating the magnets reduces a potential source of correlation between
the interferometers due to correlated environmental magnetic fields. Thus both technical noise
and fundamental thermal noise should be substantially reduced in such a suspension.
Multiple simple pendulum stages also improve the seismic isolation of the test mass for horizontal
excitation of the pendulum support point; this is a valuable feature, but requires augmentation
with vertical isolation to be effective. Vertical seismic noise can enter into the noise budget
through a variety of cross-coupling mechanisms, most directly due to the curvature of the earth
over the baseline of the interferometer. Simple pendulums have high natural frequencies for
vertical motion. Thus, another key feature of the suspension is the presence of additional vertical
65
LIGO M030023-00M
compliance in the upper stages of the suspension to provide lower natural frequencies and
consequently better isolation.
Further detail can be found in the Design Requirements Document.51
Key parameters of the test-mass suspension design are listed in Table 2; other suspensions have
requirements relaxed from these values.
Table 2 Test-mass suspension parameters
Suspension Parameter
Value
Test mass
40 kg, sapphire
Penultimate masses
fused silica, high-density glass, or low-grade sapphire
Upper masses
36 kg, stainless steel
Test mass suspension fiber
Fused silica ribbon or tapered fiber
Upper mass suspension fibers
Steel
Approximate suspension lengths
0.5 m test mass, 0.3, 0.3 m intermediate, 0.6 m top
Vertical compliance
Trapezoidal cantilever springs
Optic-axis transmission at 10 Hz
10-6
Test mass actuation
Electrostatic (acquisition), photon pressure (operation)
Upper stage actuation; sensing
Magnets/coils; incoherent occultation sensors
51
Test Mass Suspension Subsystem Design Requirements Document, T010007-00-R
66
LIGO M030023-00M
Concept/Options
The testmass mirror is suspended as the lowest mass of a quadruple pendulum as shown in
Figure 20; the four stages are in series. Sapphire is the reference design mirror substrate
material. However, the basic suspension design is compatible with fused silica masses and a
“fall-back” to this alternate may be made shortly before final design. Both materials are amenable
to low-loss bonding of the fiber to the test mass. The mass above the mirror— the intermediate
mass— is made of a moderately low-mechanical-loss glassy or crystalline material such as fused
silica, high-density glass, or low-grade sapphire.
The masses at the top are suspended from two cantilever-mounted, approximately trapezoidal,
pre-curved, blade springs (inspired by and similar to the VIRGO blade springs), and two steel
wires. The blade springs are stressed to about half of the elastic limit.
The penultimate mass is suspended from 4 cantilever springs and 2 steel wire loops. Fused silica
pieces form the break-off points at the intermediate mass. These are attached to the penultimate
and final mass using hydroxy catalysis bonding, which is demonstrated to contribute negligible
mechanical loss to the system. The upper support stages suspension wires are not vertical and
this gives some control over mode frequencies and coupling factors.
Tolerable noise levels at the intermediate mass are within the range of experience on prototype
interferometers (10-17 m/Hz) and many aspects of the technology have been tested. There are,
however, no meaningful test results at less than ~ 150 Hz. At the top-mass, the main concern is
to avoid acoustic emission or creep (vibration due to slipping or deforming parts).
Sensing (for damping) of the solid-body modes of the suspension requires an improved local
sensor (required performance ~10-12 m/Hz at 10 Hz) or an alternative servo configuration to
meet the subsystem noise performance requirements.
Actuation is applied to all masses in a hierarchy of lower force and higher frequency as the test
mass is approached. Coils and magnets are used on upper stages, with electrostatics (for
locking) and photon pressure (for operation) used on the test mass itself.
Other suspended optics will have noise requirements that are less demanding than those for the
test masses, but still stricter than the initial LIGO requirements, especially in the 10-50 Hz range.
Their suspensions will employ simpler suspensions than those for the test masses, such as the
triple suspension design for the mode cleaner mirrors shown in Figure 20.
More design detail can be found in additional subsystem documentation 52.
52
Advanced LIGO Suspension System Conceptual Design, T010103-01; N. A. Robertson, G. Cagnoli,
D. R. M. Crooks, E. Elliffe, J. Faller, P. Fritschel, S. Gossler, A. Grant, A. Heptonstall, J. Hough, H.
L\"uck, R. Mittleman, M. Perreur-Lloyd, M. V. Plissi, S. Rowan, D. H. Shoemaker, P. Sneddon, K. A.
Strain, C. I. Torrie, H. Ward, P. Willems: Quadruple Suspension Design for Advanced LIGO, Class.
Quantum Grav. Vol. 19 (2002) 4043-4058; P020001-A-R
67
LIGO M030023-00M
Figure 20 Test mass suspension design elevation view sketches.
Figure 21 Test mass suspension rendering
68
LIGO M030023-00M
R&D Status/Development Issues
The primary role of the suspension is to realize the potential for low thermal noise, and much of
the research into suspension development explores the understanding of the materials and
defines processes to realize this mission. In addition, design efforts ensure that the seismic
attenuation and the control properties of the suspension are optimized, and prototyping efforts
ensure that the real performance is understood.
The GEO-600 suspensions utilizing the basic multiple-pendulum construction, fused-silica fibers,
and hydroxy-catalysis attachments, have been in service since 2001. The systems have been
reliable and the controls function as modeled. The noise performance will be demonstrated in
2003.
Significant design and modeling of the mode-cleaner triple suspensions has taken place, and
successful careful comparison of the quadruple test-mass model with the MIT/GEO prototype has
been made.
Test mass thermal noise is one of the basic noise limits to performance of the Advanced LIGO
design. To realize the reference design performance, the following lines of research are being
pursued:



Measurement of the dissipation levels (that determine the levels of thermal noise,
according to the Fluctuation-Dissipation Theorem) of the various fused silica and
sapphire components and assembled systems, to guarantee that we can reach the levels
limited by the best material properties.
Qualification of production techniques to ensure that assembled suspensions meet all of
the specifications, including those related to thermal noise. A separate measurement of
the Q of components does not guarantee that the complete system will realize its
potential.
Verification that we do indeed achieve the expected thermal noise levels, without
significant amounts of excess noise; both stationary (best characterized in the frequency
domain) and non-stationary (studied in the time domain) performance are issues.
Development of the Advanced LIGO version of the suspension starts with the multiple pendulum
scheme based on the GEO 600 suspension, and GEO is leading the trade studies. Within that
framework, there are a number of specific questions to address, including:





choice of masses and dimensions for the masses for each stage,
choice of wires or ribbons, dimensions, means of fabrication, and attachment,
necessity of reaction masses, and designs of this system where required,
sensing and actuation systems for the damping control
establishment of the actuator hierarchy, including whether we can construct a system
without any direct actuation on the test mass, and development of electrostatic actuators
Tests for attenuation, parasitic resonances, and other defects in isolation properties (along with
consequent modifications of these pendulums) are a focus of the development effort. GEO will
characterize their system with Advanced LIGO requirements in mind. Full-scale controls and
noise test prototypes are in development and will be used to test performance against
requirements in laboratory-scale experiments.
69
LIGO M030023-00M
Work Plan
The R&D program will include work on this subsystem through full-scale tests of all principal
variants of the suspensions in the MIT LASTI testbed. By the completion of that test, the design
will have been carried through the design requirements, preliminary design, and substantially
through the final design review. A final LASTI test will serve to verify form, fit and conformance to
functional requirements. Advanced LIGO construction will commence with the final design review
and with placement of production subcontracts for all suspension subsystem components.
Fabricated components must begin arriving at the optics/vacuum preparation facilities at the two
sites in early 2007.
A consortium of the University of Glasgow, University of Birmingham, and Rutherford Appleton
Laboratory has proposed to UK funding sources (PPARC) to supply the test-mass suspensions
for Advanced LIGO43. The GEO group at the University of Glasgow is the originator of the design,
and is very well positioned to carry through with this effort.
Assembly of complete suspension subsystem units in the site facilities will start in 2006.
Suspension of the optics in the completed suspension units will be done at the time of final
installation. This will require readiness of optics processing and suspension fiber processing
systems at each site. Sufficient systems must be completed at both sites to support installation in
the interferometer vacuum chambers early in 2007.
70
LIGO M030023-00M
8. Prestabilized Laser Subsystem (PSL)
Overview
The Advanced LIGO PSL will be a conceptual extension of the initial LIGO subsystem, operating
at the higher power level necessary to meet the required Advanced LIGO shot noise limited
sensitivity. It will incorporate a frequency and amplitude stabilized 180 W laser. The Advanced
R&D program related to this subsystem will develop diode laser pumped slab or rod optical gain
stages that can be used either in injection locked power oscillators or as a multipass power
amplifier.
Functional Requirements
The main requirements of the PSL subsystem are output power, and amplitude and frequency
stability. Table 3 lists the reference values of these requirements. Changes in the readout system
allow some requirements to be less stringent with respect to initial LIGO; the extension to lower
frequency provides the principal challenge.
Table 3 PSL Requirements
Requirement
Value
TEM00 Power
180 W
Non-TEM00 Power
<5 W
Frequency Noise
10 Hz/Hz1/2 (10 Hz)
Amplitude Noise
2×10-9 /Hz1/2 (10 Hz)
Beam Jitter
2×10-6 rad/Hz1/2 (100 Hz)
RF Intensity Noise
0.5 dB Above Shot Noise at 25 MHz for 150 mW
TEM00 Power: Assuming an optical throughput of 0.67 for the input optics subsystem, the
requirement of 120 W at the interferometer input gives a requirement of 180 W PSL output.
Non-TEM00 Power: Modal contamination of the PSL output light will mimic shot noise at the
mode cleaner cavity, producing excess frequency noise. A level of 5 W non-TEM00 power is
consistent with the input optics frequency-noise requirements.
Frequency Noise: Frequency noise couples to an arm cavity reflectivity mismatch to produce
strain noise at the interferometer signal port. The requirement is obtained based on a model with
an additional factor of 105 frequency noise suppression from mode cleaner and interferometer
feedback, a 0.5% match in amplitude reflectivity between the arm cavities (a conservative
estimate for the initial LIGO optics), and a signal recycling mirror of 10% transmissivity.
Amplitude Noise: Laser amplitude noise will cause strain noise in two main ways. The first is
through coupling to a differential cavity length offset. The second and larger coupling is through
unequal radiation pressure noise in the arm cavities. Assuming a beamsplitter of reflectivity
501%, the requirement is established.
Beam Jitter Noise: The coupling of beam jitter noise to the strain output is through the
interferometer optics misalignment. Based on a model of a jitter attenuation factor of 1000 from
the mode cleaner, a nominal optic alignment error of 10-9 rad rms imposes the requirement on
higher order mode amplitude.
RF Intensity Noise: The presence of intensity noise at the RF modulation frequency directly
produces strain noise. The noise is limited with the requirement above.
71
LIGO M030023-00M
Concept/Options
The conceptual design of the Advanced LIGO PSL is similar to that developed for initial LIGO. It
will involve the frequency stabilization of a commercially engineered laser with respect to a
reference cavity. It will include actuation paths for coupling to interferometer control signals to
further stabilize the beam in frequency and in intensity. Three options for the laser design are
under study: a slab injection-locked stable-unstable resonator, a rod injection-locked stable
resonator, and a multipass power amplifier. The technology will be selected in early 2003. The
control system of the Advanced LIGO PSL, including amplitude and frequency servos, will be
largely adapted and extended from the initial LIGO design.
R&D Status/Development Issues
Three approaches to the development of the laser are being pursued. The target for the power
from the laser head is 180 W to accommodate some losses to spatial mismatch from the source
laser to the desired TEM00 mode. Sketches of the proposed solutions are shown in Figure 22.
QR
output
pump
BP
f
f
f
f
QR
HR@1064
HT@808
YAG / Nd:YAG / YAG
3x 7x40x7
Figure 22 Three approaches to the high-power laser head. At left, an injection-locked
stable-unstable resonator (Adelaide); middle, and end-pumped zig-zag amplifier
(Stanford); at right, an injection-locked end-pumped rod system (LZH).
In one approach, the Adelaide University group is prototyping a system in which a low-noise, low
power master oscillator injection locks a high power stage, formed with a diode-pumped slab
crystal situated in a stable-unstable resonator.
An approach, undertaken by Stanford University, uses the master oscillator-power amplifier
(MOPA) configuration. In this approach, the output of a master oscillator is passed one or more
times through a series of gain elements. This is the laser configuration in use for the initial LIGO,
developed by Lightwave Electronics Corporation based upon earlier Stanford work, which
provides 10 W output power. The Stanford group is extending the MOPA design to 180W-output
power by using the 10-W laser as a master oscillator and employing additional amplifier stages.
The third approach, pursued at the Max Planck Institute for Gravitational Wave
Research/University of Hannover and the Laser Zentrum Hannover, is an end-pumped rod
resonator that is injection locked to a master oscillator. It is based on experience with the GEO600 laser, but taking the approach from ~25 W to ~200 W.
The overall goal of this advanced R&D effort is to develop the power laser technology to the point
where industrial participation in engineering a reliable unit can begin. The Max Planck group will
propose to German funding agencies to supply the laser system for Advanced LIGO, and is
leading the downselect and conceptual design effort.
72
LIGO M030023-00M
Work Plan
The parallel approach to the development of high power lasers is proceeding, with all three
groups approaching the intermediate goal of a 100 W laser. Comparative tests of the three laser
designs, with participation from LIGO, are planned for early 2003. After the selection is made, an
effort with an industrial partner, the Laser Zentrum Hannover, similar to our practice in initial
LIGO, will be undertaken to engineer a reliable unit that will meet the LIGO availability goal. Tests
of a complete full-power PSL will be made in the LASTI installation in late 2005. The PSL
subsystem design work will proceed in parallel with the laser fabrication, so that the complete
subsystem will be ready for installation in early 2007.
Max Planck Institute for Gravitational Wave Research/University of Hannover and the Laser
Zentrum Hannover are proposing to supply the PSL systems for Advanced LIGO as a German
contribution to the partnership in Advanced LIGO. The University expects to propose project
funding for this to the German funding agency in the next year. They are already supported for
the development phase.
73
LIGO M030023-00M
9. Input Optics Subsystem (IO)
Overview
The Advanced initial LIGO subsystem will be an extension of the initial LIGO Input Optics design
to the higher specified power and lower noise level of Advanced LIGO. The IO will consist
primarily of beam conditioning optics including Faraday Isolators and phase modulators, a
triangular input mode cleaner, and an interferometer mode-matching telescope.
Functional Requirements
The functions of the IO subsystem are to provide the necessary phase modulation of the input
light, to spatially and temporally filter the light on transmission through the mode cleaner, to
provide optical isolation as well as distribution of interferometer diagnostic signals, and to mode
match the light to the interferometer with a beam-expanding telescope. Table 4 lists the
requirements on the output light of the IO II subsystem.
Table 4 Advanced initial LIGO requirements
Requirement
Value
Optical Throughput
0.67 (net input to TEM00 out)
Non-TEM00 Power
<5%
Frequency Noise
3×10-3 Hz/ Hz1/2 (10 Hz)
Beam Jitter
1×10-9 rad RMS
The Input Optics has to deliver 120 W of conditioned power to the advanced LIGO interferometer.
The optical throughput requirement ensures that the required TEM00 power will be delivered. The
cavities of the main interferometer will accept only TEM00 light, so the IO must remove the higherorder modes and its beam-expanding telescope must couple 95% of the light into the
interferometer.
The IO reduces the frequency, and beam-jitter noise of the laser. The suspended mode cleaner
serves as an intermediate frequency reference between the PSL and interferometer. Beam jitter
(pointing fluctuation) appears as noise at the interferometer output signal through optical
misalignments and imperfections. The nominal optic alignment error of 1×10-9 rad imposes the
requirement in Table 4. Further details can be found in the IO Design Requirements document 53.
Concept/Options
The schematic layout of the IO is displayed in Figure 23, showing the major functional
components. The development of the IO for Advanced LIGO will require a number of incremental
improvements and modifications to the initial LIGO design. Among these are the needs for larger
mode cleaner optics and suspensions to meet the Advanced LIGO frequency noise requirement,
and increased power handling capability of the Faraday Isolator and phase modulators.
53
Advanced LIGO Input Optics Design Requirements Document, T020020-00
74
LIGO M030023-00M
Figure 23 Schematic diagram of the Advanced LIGO Input Optics (IO) subsystem.
Phase modulation for use in the length and angle sensing systems is applied using electro-optic
crystals. Faraday isolators are used to prevent parasitic optical interference paths to the laser and
to obtain information for the sensing system.
The mode cleaner is an in-vacuum suspended triangular optical cavity. It filters the laser beam by
suppressing directional and geometric fluctuations in the light entering the interferometer, and it
provides frequency stabilization both passively above its pole frequency and actively through
feedback to the PSL. Noise sources considered in design studies include sensor/actuator and
electronic noise, thermal, photothermal and Brownian motion in the mode cleaner mirrors, and
radiation pressure noise. The mode cleaner will use 15-cm diameter, 7.5-cm thick fused silica
mirrors. The cavity will be 17 m in length, with a finesse of 2000, maintaining a stored power of
~100 kW. A triple pendulum (part of the suspensions subsystem) will suspend the mode cleaner
mirrors so that seismic and sensor/actuator noise does not compromise the required frequency
stability.
Finally, the mode-matching telescope, which brings the beam to the final Gaussian beam
parameters necessary for interferometer resonance, will be similar to the initial LIGO design, but
will use two (rather than three) reflective spherical mirrors. The third element will consist of an
adaptive optical lens that will allow for in situ adjustment of mode matching without the need for
vacuum excursions. This design allows for optimization of mode-matched power by having
independent adjustment of two degrees of freedom, waist size and position, over a wide range of
modal space.
Further documentation of the design can be found in the Input Optics Conceptual Design
Document54.
54
Advanced LIGO Input Optics Subsystem Conceptual Design Document, T020027-00
75
LIGO M030023-00M
R&D Status/Development Issues
The IO subsystem has completed its Design Requirements and Concept Review and is now in
preliminary design. Development of the IO focuses on the need for power handling at the 180 W
level and the corresponding development of the Faraday Isolators and phase modulators. For the
Faraday Isolator, both wavefront distortion and depolarization effects need to be addressed. A
new design55 providing compensation for polarization distortion has shown good isolation up to
the maximum test power of 85W. For modulators, we are studying 5 different materials:
potassium titanyl phosphate (KTP), potassium titanyl arsenate (KTA), rubidium titanyl arsenate
(RTA), rubidium titanyl phosphate (RTP), and lithium niobate (LiNb03). Initial testing suggests that
several of these are good candidates, potentially using a compensation approach similar to that
for the Faraday Isolator.
Work Plan
Development of high power Faraday Isolators and phase modulators is proceeding under the
University of Florida Advanced R&D program, and the subsystem lead role will remain with the
University of Florida as for initial LIGO. A complete end-to-end test of the IO will be performed at
the LASTI facility in conjunction with the mode cleaner suspension testing and the pre-stabilized
laser testing in 2005. Installation will commence in 2007.
E. Khazanov, N. Andreev, A. Babin, A. Kiselev, O. Palashov, and D. H. Reitze, “Suppression of
Self-Induced Depolarization of High-Power Laser Radiation in Glass-Based Faraday Isolators”, J. Opt.
Soc. Am B. 17, 99-102 (2000)
55
76
LIGO M030023-00M
10. Core Optics Components (COC)
Overview
The Advanced LIGO COC will involve a significant change from the initial LIGO COC to meet the
higher power levels and improved shot-noise and thermal-noise limited sensitivity required of the
Advanced LIGO interferometer. Many of the fabrication techniques developed for the fused silica
initial LIGO COC will be directly applicable to the optics production. However, sapphire is adopted
as the baseline substrate material for the test masses in Advanced LIGO. Sapphire is chosen
because of its higher mechanical Q, speed of sound, and density, all of which contribute to a
significant reduction in the internal thermal noise leading to an improvement of the detector
sensitivity by a factor of 2 over fused silica at 100 Hz, and more at higher frequencies. The larger
mass is needed to keep the radiation reaction noise to a level comparable to the suspension
thermal noise. Its higher thermal conductivity reduces the thermal lensing due to absorbed laser
power. Sapphire does have a greater thermal expansivity, leading to a thermoelastic noise
contribution. An R&D effort is underway to develop sapphire in a quality and size appropriate to
serve as test mass material. The optical coatings must also undergo development to achieve the
combination of low mechanical loss (for thermal noise) while maintaining low optical loss.
Functional Requirements
The COC subsystem consists of the following optics: power recycling mirror, signal recycling
mirror, beam splitter, folding mirror, input test mass, and end test mass (see Figure 14). The
following general requirements are placed on the optics:





the radius of curvature and surface figure must maintain the TEM00 spatial mode of the
input light;
the optics microroughness must be low enough to limit scatter to acceptable levels;
the substrate and coating optical absorption must be low enough to limit the effects of
thermal distortion on the interferometer performance;
the optical homogeneity of the transmitting optics must be high enough to preserve the
shape of the wavefront incident on the optic;
the intrinsic mechanical losses, and the optical coating mechanical losses, must be low
enough to deliver the required thermal noise performance
Table 5 lists the COC test mass requirements for both fused silica and sapphire materials under
consideration for the different types of optics.
Table 5 COC test mass requirements
Sapphire
Surface figure
(deviation from sphere over central 12 cm)
Micro-roughness
Silica
1 nm RMS
0.1 nm RMS
Optical homogeneity
(in transmission through 15 cm thick substrate, over
central 8 cm)
Optical absorption
Substrate mechanical Q
Optical coating optical loss
20 nm pk-pk, double pass
<20 ppm/cm
<0.5 ppm/cm
2×108
3×107
0.5 ppm/bounce
77
LIGO M030023-00M
2×10-5 (goal)
Optical coating mechanical loss
As the table shows, the figure, roughness and homogeneity requirements are the same for both
materials. The absorption requirement is reduced for sapphire because its relatively higher
thermal conductivity reduces thermal distortion for a given heat input.
Concept/Options
Sapphire is the reference design for the input and end test mass material because of its promise
of reduced internal thermal noise and due to better thermal distortion properties. Internal thermal
noise is a limit to interferometer sensitivity at the noise minimum near 100 Hz. As insurance
against the risks involved in the sapphire development effort, the option of using ultra-low optical
absorption fused silica for the test masses is being preserved. The final decision to retain
sapphire as the critical test mass material is scheduled before production fabrication must begin.
Fabrication of fused silica to meet most of the requirements in the above table has already been
demonstrated and is not expected to involve research and development; work would be required
to ensure acceptable mechanical losses of fused silica in large substrates, although very low
losses have been seen in smaller samples. The material properties of fused silica would require
significantly more reliance on the thermal compensation system (see 11. Auxiliary Optics
Subsystem (AOS)).
The beam splitter requirements are met by the best presently available low absorption fused silica
and the power and signal recycling mirrors of LIGO-I class fused silica. These mirrors do not have
the same noise or power handling requirements as the test masses, so fused silica, being more
readily available, is chosen.
The very long lead time for production of substrates, for polishing, and for coating (for either
substrate choice) makes this the critical path item in the Advanced LIGO schedule. Early funding
for purchase of the substrates is needed to maintaining the present planned schedule.
R&D Status/Development Issues
Sapphire research and development is well underway. In partnership with industry we are
developing the techniques to grow, polish and coat sapphire to the Advanced LIGO requirements;
full size boules (which can be tailored to the 32cm diameter testmass size) of sapphire have been
produced and are now undergoing an initial polishing phase to allow characterization of the
absorption, birefringence and optical homogeneity, demonstrating suitability for the Advanced
LIGO test masses. This R&D resembles that employed in initial LIGO, in which a pathfinder
process demonstrated that fused silica optics could be brought to the initial LIGO specifications.
Sapphire is a very hard material that requires special polishing. It must be polished to give a
smooth surface both on small scales (microroughness), and large scales (surface figure).
Samples have been polished to our requirements. In addition, compensation may be needed for
the optical inhomogeneities experienced by the wavefront as it is transmitted through the nonuniform optic. Four approaches to optical compensation have been explored; at CSIRO there has
been work on ion milling, fluid jet polishing and corrective coating, at Goodrich (see Figure 24)
compensation has already been demonstrated on a 250 mm optic using computer controlled
corrective polishing. Though ion milling is attractive we have chosen corrective polishing as our
baseline since the infrastructure for handling large pieces already exists.
78
LIGO M030023-00M
Figure 24 Sapphire piece used in the spot-polishing compensation demonstration; 25cm
diameter sample (photo courtesy Goodrich).
Sapphire substrate optical absorption also is receiving attention. Present measurements of a
large set of sapphire test pieces indicate baseline absorption of 50-80 ppm/cm. The R&D effort is
aimed at reducing this absorption to 20 ppm/cm. Investigations are underway examining the
effect of the purity and preparation of raw material, segregation of impurities during growth, and
effects of annealing temperature, duration and atmosphere. These studies have suggested that a
simple selection of the best material will not be sufficient and that it will be necessary to do post
growth processing, possibly including sample harvesting, regrowth and high temperature
purification. Preliminary results, at the time of writing this proposal, indicate that such processing
can yield absorption of 50 ppm/cm with regions of 20 ppm/cm. With the use of thermal
compensation (see next section), 50 ppm/cm would be acceptable, but 20 ppm/cm gives
desirable margin in the design. We will continue to pursue this through the development stage
(through early 2004).
A very active program to characterize and reduce the mechanical loss in the coatings has made
progress. The principal source of loss in conventional optical coatings has been determined by
our research to be associated with the tantalum pentoxide, either due to material losses or due to
stresses induced during the coating process. Several alternative materials and processes are
being explored with multiple vendors. We have a goal of an approximate factor of ten reduction in
the loss, as a coating mechanical loss at this level ensures the coating thermal noise does not
significantly reduce the sensitivity of the instrument. We have seen reductions of 2.5 in selected
samples of exploratory coatings.
79
LIGO M030023-00M
Work Plan
The sapphire R&D effort will culminate in early 2003, when a decision will be made on whether to
proceed with production of sapphire test masses, or instead rely on the fallback plan of ultralow
absorption fused silica. Following this selection, fabrication will proceed with the plan for first
articles to be available in 2006.
The time scale for developing a satisfactory coating, with appropriate optical and mechanical
losses, is associated with the commencement of coatings on the production optics at the end of
2005.
80
LIGO M030023-00M
11. Auxiliary Optics Subsystem (AOS)
Overview
The AOS for Advanced LIGO is an extension of this subsystem for initial LIGO, and will
accommodate the planned higher laser power and additional signal-recycling mirror. The AOS is
responsible for transport of interferometer output beams and for stray light control. It includes
beam reducing telescopes, and beam dumps and baffles. An additional element of this
subsystem is active optics thermal compensation, where compensatory heating of an optic is
used to cancel thermal distortion induced by absorbed laser power. It also includes the photon
actuator, which uses light pressure to adjust the length of the interferometer arms. AOS also
covers the addition of an output mode cleaner.
Functional Requirements
The conventional subsystem requirements relate to control of interferometer ghost beams and
scattered light, delivery of interferometer pickoff beams to the ISC subsystem, and maintenance
of the surface figure of the core optics through active thermal compensation. While the
requirements on these elements are somewhat more stringent than for the initial LIGO design, no
significant research and development program is required to meet those requirements.
There are elements which are new to the Advanced LIGO design for which the requirements will
be numerically determined as part of the systems flowdown:



Active Thermal Distortion Compensation: The axisymmetric thermal lens must be
corrected sufficiently to allow the interferometer to “cold start”; the compensation may
also be required to correct for small (cm-) scale spatial variations in the substrate
absorption.
Photon Actuator: Forces must be applied to the test mass during the operation of the
interferometer to maintain the operating length without compromising the mechanical
losses of the system. The photon actuator must have sufficient authority to perform the
actuation, without adding noise above a negligible level.
Output Mode Cleaner: The length sensing system requires that non-TEM00 light power
at the antisymmetric output port be reduced substantially to allow a small local-oscillator
level to be optimal and thus to maintain the efficiency of the overall shot-noise-limited
sensing.
Concept/Options
The AOS conventional elements consist of low-aberration reflective telescopes that are placed in
the vacuum system to reduce and relay the output interferometer beams out to the detectors, and
baffles of absorptive black glass placed to catch stray and “ghost” beams in the vacuum system.
The elements must be contamination free and not introduce problematic mechanical resonances.
Because of the increased interferometer stored power, the AOS for Advanced LIGO will involve
careful attention to control of scattered light, and will require greater baffling and more beam
dumps than for initial LIGO.
The thermal compensation approach involves adding heat, which is complementary to that
deposited by the laser beam, using two complementary techniques: a ring heater that deals with
circularly symmetric distortions, and a directed laser that allows uneven absorption to be
corrected.
81
LIGO M030023-00M
The frequency-dependent transmission and filtering properties required of the output mode
cleaner depend on the ISC readout scheme chosen (DC or RF) and will be determined in an
integrated manner with the choice of the readout scheme. ACIGA4, with their expertise in sensing
systems, will aid in the design of the output mode cleaner, and ACIGA is proposing to contribute
materially in the fabrication and installation of an output mode cleaner. This complements their
efforts to study variable transmission signal recycling mirrors.
The photon actuator employs an auxiliary laser beam that is reflected from the optic to be
actuated upon; the laser amplitude is modulated to control the radiation force. Lasers of several
watts can deliver the very small forces required.
R&D Status/Development Issues
Development of active optic thermal compensation is proceeding under the LIGO advanced R&D
program. A model of the thermal response of the interferometer in a modal basis has been
developed56 and used extensively to make predictions for the deformations and of the possible
compensation. A prototype has successfully demonstrated thermal compensation, in excellent
agreement with the model, using both the ring heater and directed laser techniques 57. A detailed
characterization of the spatial distribution of absorption in Sapphire is needed to quantify the
correct approach for Advanced LIGO; this will be available from the Core Optics Components test
articles in early 2003. This will be complemented with a physical optics model using FFT beam
propagation techniques, using these phase maps as input.
The photon actuator will require a more complete systems model for the dynamic range and
frequency response to be precisely defined. The intensity stabilization of the source laser is likely
to present the only challenge, but present models do not indicate difficulty with the design.
There are two potential designs for the output mode cleaner, dependent on the chosen
gravitational wave readout technique. If RF sidebands are used, then the output mode cleaner
will be effectively a copy of the input mode cleaner, as it must pass efficiently both the carrier and
sidebands. If DC readout were used, the output mode cleaner would be a short, rigid cavity,
mounted in one of the output HAM chambers. Both the VIRGO Project and GEO-600 use output
mode cleaners in their initial design. We plan to start with a study of their approach and the
experience with those systems. The principal design challenges lie in the interface to the
Interferometer Sensing and Control. The cavity must be aligned with the nominal TEM00 axis of
the interferometer, but the bulk (by several orders of magnitude) of the output power will be in
higher-order modes; determining the correct alignment is thus non-trivial. The length control, in
particular the lock acquisition sequence, also adds complexity.
Work Plan
Work on the active optics thermal compensation is proceeding under the advanced R&D
program. A complete prototype thermal compensation system will be tested in the ACIGA Gingin
facility in 2003. A prototype photon actuator is being developed with a test on the Caltech 40
Meter Interferometer prototype planned for 2004. The output mode cleaner will be studied using
the modeling tools developed for the Mode Cleaner cavity (to which this may bear a strong
resemblance) and overall interferometer controls models; a small-scale tabletop prototype will be
developed if indicated to ensure that the models are complete to support the ISC design schedule
(with a Preliminary Design Review in mid-2004), with the design and fabrication profiting from the
56
R.G.Beausoleil, E. D'Ambrosio, W. Kells, J. Camp, E K.Gustafson, M.M.Fejer: Model of Thermal
Wavefront Distortion in Interferometric Gravitational-Wave Detectors I: Thermal Focusing, to appear in
JOSA B; http://arxiv.org/abs/gr-qc/0205124
57 Adaptive thermal compensation of test masses in Advanced LIGO, R. Lawrence, M. Zucker, P.
Fritschel, P. Marfuta, D. Shoemaker, Class. Quant. Gravity 19 (2002)
82
LIGO M030023-00M
suspension and core optics groups. The design process for the beam dumps, baffles, reducing
telescopes will resemble that for the initial LIGO design with a planned installation starting in
2007.
ACIGA is proposing to contribute materially in the fabrication and installation of an output mode
cleaner. This complements their efforts to study variable transmission signal recycling mirrors.
83
LIGO M030023-00M
12. Interferometer Sensing and Controls Subsystem (ISC)
Overview
This subsystem comprises the length sensing and control, the alignment sensing and control, and
the overall controls infrastructure modifications for the Advanced LIGO interferometer design. The
infrastructure elements will be modified to accommodate the additional control loops in the
reference design. The single most significant difference in the Advanced LIGO subsystem is the
addition of the signal recycling mirror and the resulting requirements on the controls.
Functional Requirements
Table 6 lists significant reference design parameters for the interferometer length controls.
Table 6 Significant Controls Parameters
Configuration
Signal and power recycled Fabry-Perot
Michelson interferometer


Controlled lengths



differential arm length (GW signal)
near-mirror Michelson differential
length
common-mode arm length
(frequency control)
power recycling cavity resonance
signal recycling mirror control
Controlled angles
2 per DOF above, 12 in total
Main differential control requirement
10-14 m rms
Shot noise limited displacement sensitivity
410-21 m/Hz
Angular alignment requirement
10-9 rad rms
The requirements for the readout system are in general more stringent than those for initial LIGO.
The differential control requirement is a factor of 10 smaller, as is the angle requirement, and the
additional degrees of freedom add complexity. Integration with the thermal compensation system
and the gradual transition from a “cold” to a “hot” system will be needed.
In spite of the increased performance requirements for Advanced LIGO, significant simplification
in the controls system is foreseen because of the large reduction in optic residual motion afforded
by the active seismic isolation and suspension systems. Reduced core optic seismic motion can
be leveraged in two ways. First, the control servo loop gain and bandwidth required to maintain a
given RMS residual error can be much smaller. Second, the reduced control bandwidths permit
aggressive filtering to block leakage of noisy control signals from imperfect sensor channels into
the measurement band above 10 Hz. While control modeling is just getting started, this latter
benefit is expected to significantly relieve the signal-to-noise constraints on sensing of auxiliary
length and alignment degrees of freedom.
84
LIGO M030023-00M
Concept/Options
The signal-recycled configuration is chosen to allow tunability in the response of the
interferometer. This is useful for the broadband tuning to control the balance of excitation of the
mirrors by the photon pressure, and the improvement in the readout resolution at 100-200 Hz. A
narrow-band instrument (to search for a narrow-band source, or to complement a broad-band
instrument) can also be created via a change in the signal recycling mirror transmission. An
example of possible response curves for a single signal recycling mirror transmission is shown in
Figure 25.
Another important advantage of the signal recycled configuration is that the power at the
beamsplitter for a given peak sensitivity can be much lower; this helps to manage the thermal
distortion of the beam in the beamsplitter, which is more difficult to compensate due to the
elliptical form of the beam and the significant angles in the substrate.
10
-22
h(f) /Hz
1/2
10
-21
10
-23
sap
phi
re
10
10
-24
the
rm
oel
ast
ic
noi
se
-25
10
1
10
2
10
3
Frequency (Hz)
Figure 25 Strain sensitivity curves for a narrowband interferometer. With a single signal
recycling mirror chosen to give optimum performance around 700 Hz, good performance
between ~500–1000 Hz can be achieved by tuning the signal mirror position microscopically; the set of curves shown span a mirror motion of about 0.01 wavelength. At the
lower end of the octave, sapphire’s thermoelastic noise limits the performance; at higher
frequencies, above ~500 Hz, sapphire has a clear advantage over fused silica for
narrowband performance (modeled using Bench58)
58
L. S. Finn, http://gravity.psu.edu/~lsf/Benchmarks/main.html
85
LIGO M030023-00M
Most length sensing degrees-of-freedom will be sensed using RF sidebands in a manner similar
to that in initial LIGO. There are two options for the main gravitational readout. One is to use an
RF system similar to initial LIGO, in which variants of the Pound-Drever-Hall scheme are used to
derive zero-crossing error signals. The other is to shift the output of the interferometer slightly
away from the dark fringe and to use deviations from the setpoint as a measure of the strain. This
approach considerably relaxes the requirements on the laser frequency; the nominally more
stringent requirement on the baseband intensity fluctuations appears tractable. Two
considerations will inform the choice of approach: (i) A complete quantum-mechanical analysis of
the two readout schemes to determine which delivers the best sensitivity; and (ii) Requirements
imposed on the laser and modulation sources due to coupling of technical noise.
Alignment sensing and control will be accomplished by wavefront sensing techniques similar to
those employed in initial LIGO.
The much lower seismic noise in Advanced LIGO will allow smaller control bandwidths for the
test-mass actuators; on the other hand, forces to keep the system stable against photon pressure
will need to be exerted. In general, the active isolation system and the multiple actuation points
for the suspension provide an opportunity to optimize actuator authority in a way not possible with
initial LIGO, but will also lead to a more complex system for initial acquisition of operation
(“locking”) as well as during operation.
R&D Status/Development Issues
The signal-recycled optical configuration chosen for Advanced LIGO (see Figure 14) challenges
us to design a sensing and control system that includes the additional positional and angular
degrees of freedom introduced by the signal-recycling mirror. Several straightforward extensions
of the sensing system for initial LIGO have been considered. Mason 59, Delker60 and Shaddock61
have demonstrated locking of signal-recycled tabletop interferometers using variants of the initial
LIGO asymmetry method, adapted in more or less radical ways to accommodate the additional
signal recycling cavity degrees of freedom.
These tabletop experiments and their associated simulations have shown that it is not difficult to
arrive at non-singular sensing schemes by adding an additional RF modulation which, through
selection of resonant internal lengths, preferentially probes the new cavity coordinates. However
there is a great deal of subtlety in choosing parameters to decouple the coordinate readouts
adequately to establish a simple, robust control design while realizing the high strain signal-tonoise required.
A detailed prototype test of the control system is underway in GEO (Glasgow), with results
expected in early 2003. An engineering control demonstration is in preparation in the LIGO 40
Meter Interferometer (Caltech); it will be fed with information from the GEO effort, and will strive to
make a complete emulation of the control system using the target control hardware and software.
Locking and operation of the system will be studied.
The selection of the readout scheme involves a trade-off between optimal signal detection and
sensing noise (of both fundamental quantum origin and technical noise). The signal-recycling
J. Mason, “Length Sensing and Noise Issues for a Advanced LIGO RSE Interferometer,” PAC
Meeting, 1 May 2000 (http://www.ligo.caltech.edu/docs/G/G000119-00.pdf)
60 T. Delker, G. Mueller, D. Tanner, and D. Reitze, “Status of Prototype Dual Recycled-Cavity
Enhanced Michelson Interferometer,” LSC Meeting, 15 Aug 2000
(http://www.ligo.caltech.edu/docs/G/G000275-00.pdf)
61 M. Gray, D. Shaddock, C. Mow-Lowry, and D. McClelland, “Tunable Power-Recycled RSE
Michelson Interferometer for Advanced LIGO.” LSC Meeting, 15 Aug 2000
(http://www.ligo.caltech.edu/docs/G/G000227-00.pdf)
59
86
LIGO M030023-00M
mirror, detuned from perfect resonance, generates a coupling between the shot noise and the
mirror motion induced by radiation pressure noise. This causes the GW signal to appear
simultaneously in both the phase and amplitude quadratures of the output field (a significant
departure from initial LIGO and other first-generation detectors). The DC and RF readout
schemes respond to the frequency-dependent optimal signal quadrature differently and the goal
is to find a best compromise62.
To accommodate the needs for wideband multi-frequency auxiliary length readouts, the DC strain
readout, and high-frequency wavefront sensing, characterization of photodiodes will be
undertaken. As for initial LIGO detectors, the first steps will be surveys of commercial devices and
those developed by colleagues in other projects. This phase will likely be followed in one or more
cases by development work to customize or to improve performance and to optimize the
electronic amplifiers that mate to these detectors.
Though not necessarily required, lower noise analog-to-digital and digital-to-analog converters
would be of great benefit in the design of the sensing and control signal chain. We will prototype
board circuitry and software to integrate these converters into our VME-based digital control
environment. We also will experiment with new topologies and circuits for the critical analog
signal conditioning filters that match the dynamic range of the converters to that of the physical
signals they deal with.
Work Plan
The controls configuration will be developed based upon the experience gained from the use of
signal recycling in the GEO 600 interferometer, experiments conducted at several institutions in
the LSC including pivotal work at the GEO 10 meter prototype from which results are due in early
2003. The final test takes place in the Caltech 40 Meter Interferometer for which the construction
will be complete in late 2003; it will inform the design in mid-05, and fabrication can start shortly
thereafter. The LIGO Laboratory will manage the design and fabrication of the controls subsystem
as it did during initial LIGO construction.
A. Buonanno, and Y. Chen, “Quantum noise in second-generation signal-recycled laser
interferometric gravitational wave detectors,” Phys. Rev. D 64, 042006 (2001); A. Buonanno, Y. Chen,
and N. Mavalvala, “Quantum noise in laser interferometer gravitational wave detectors with a
heterodyne readout scheme," to be submitted to Phys. Rev. D (2003), P020034-00-R
62
87
LIGO M030023-00M
13. Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ)
Overview
The differences between the initial LIGO and Advanced LIGO Data Acquisition, Network &
Supervisory Control (DAQ) requirements derive from the improved sensitivity and performance
of the Advanced LIGO interferometers. We specify an increased ADC dynamic range to more
easily accommodate the great disparity between narrowband features and lower broadband
noise, and a greater number of channels to monitor a greater number of active control systems
Functional Requirements
The principal Advanced LIGO reference design parameters that will drive the data acquisition
subsystem requirements are summarized in Table 7.
Table 7 Principal impacts of the Advanced LIGO Reference Design on Data Acquisition
and Data Analysis Systems. The number of Degrees of Freedom (DOF) is indicated for
the main interferometer to give a sense of the scaling.
Parameterization
Advanced LIGO
Reference
Design
> 121 dB
(20 bits)
Initial LIGO
Implementation
Comment
96 dB
(16 bit ADC)
Acquisition System
Maximum Sample
Rate, s/s
Active cavity
mirrors, per
interferometer
Active seismic
isolation system
servos
16384
16384
7
6
Range of h[t] is determined by
narrowband feature amplitude
and broadband noise floor.
Effective shot noise frequency
cutoff is well below fNyquistt
(8192 Hz)
Signal Recycling Mirror will be
added.
11 chambers per
interferometer; 18
DOF per
chamber; total,
198 DOF
2 end chambers
per
interferometer,
total, 12 DOF
Axial and angular
alignment &
control, per
interferometer
(4 km / 2 km)
SUS DOF : 42
L DOF: 5
( ,  ) DOF:12
SUS DOF: 36
L DOF: 4
( ,  ) DOF: 10
Total Controlled
DOFs
257
62
Whitened h[t]
dynamic range
Iinitial LIGO uses passive
isolation with an external 6 DOF
pre-isolator on end test masses;
Advanced LIGO uses active
multistage 6 DOF stabilization
of each seismic isolation
platform.
Advanced LIGO has two
additional cavities. Each
actively controlled mirror
requires 6 DOF control of
suspension point plus ( , , L )
control of the bottom mirror.
Relative comparison of servo
loop number for maintaining
resonance in the main cavities
(PSL and IO not included)
The reference Advanced LIGO design will have a broadband noise floor between narrowband
features that is limited by radiation pressure noise at a level h[f]~2-3 10-24 1/√Hz (see Figure 15),
~ 10x lower than the initial LIGO design. Our present best estimate is that the Advanced LIGO
88
LIGO M030023-00M
dynamic range requirement for whitened signals at the interferometer output port will be ~ 10x
greater than the initial LIGO baseline, leading to a working requirement for ADC resolution of 20
bits.
Advanced LIGO will require monitoring and control of many more degrees of freedom (DOF) than
exist in the initial LIGO design. The additional DOFs arise primarily from the active seismic
isolation, with a smaller contribution from the move to multiple pendulum suspensions and the
additional suspended mirror. Table 7 summarizes these modifications. Both the suspension and
the seismic isolation systems will be realized digitally (except for the sensors and actuators) and
the DAQ will need to capture a suitable number of the internal test points for diagnostics and
state control (as is presently done for the initial LIGO digital suspension controllers).
Referring to Table 7, the number of loops per interferometer that are required for Advanced LIGO
is seen to be ~ 250. This is to be compared to ~ 60 for initial LIGO. The number of channels that
the DAQ will accommodate from the interferometer channels for Advanced LIGO will reflect this
4X increase in channel number.
Table 8 presents approximate channel counts classified by sample bandwidth for Advanced LIGO
and compares these to initial LIGO values. These represent the total volume of data that is
generated by the DAQS + GDS; a significant fraction of these data are not permanently acquired.
Nonetheless, the ability to acquire all available channels must be provided.
Table 8 DAQ Acquisition Data Channel Count and Rates63
System
Channels, LHO + LLO
Total
(Total: 3 x IFO + 2 x PEM)
Acquisition Rates, MB/s
LHO + LLO
Total
Recorded Framed Data
Rates, MB/s
LHO + LLO
Total
Advanced
LIGO
Reference
Design
5464 + 3092
8556
Initial LIGO64
Comments
1224 + 714
1938
29.7 + 16.3
46
11.3 + 6.1
17.4
LIGOII will have ~4.5X
greater number of
channels.
DAQS II has ~3X total data
acquisition.
DAQS II has ~2X total
framed data recording rate.
12.9 + 7.7
20.6
6.3 + 3.5
9.8
Concept/Options
The driving features of the Advanced LIGO hardware design are the increase in channel count
and increase in data word length for the main sensing channels. The initial LIGO 16 bit ADCs will
be exchanged for newer 32 bit ADCs (note: 20 bits are actually specified). Not all DAQS channels
require the greater dynamic range. Moreover, the increase in acquisition bandwidth with double
data-word size dictates that only those channels requiring the increased dynamic range should be
upgraded.
63
These rates include are derived from LIGO I rates with scaling as indicated in the table. Data rates
quoted include a number of diagnostics channels and this rate is greater than the framed data rate which
eventually is recorded for long term storage.
64 LIGO I channel counts differ by site and interferometer; representative values are indicated.
89
LIGO M030023-00M
The additional data channels required for the newer seismic isolation and compound suspension
systems will require additional ADCs distributed throughout the experimental hall CDS racks.
Additional racks will be required and can be placed alongside the present CDS racks within the
experimental halls. In those cases where there is interference with existing hardware, racks will
need to be located further away, at places previously set aside for LIGO expansion. Additional
cable harnesses for new channels will be accommodated within the existing cable trays.
The initial LIGO data acquisition processors do not have excess capacity sufficient to
accommodate the increase in acquisition rate and will need to be upgraded. The upgrade will be
a combination of updating the hardware technology and using a greater number of processors.
The existing fiber optic infrastructure will accommodate the Advanced LIGO DAQS changes
without requiring an upgrade. The DAQ framebuilder and on-line mass storage systems will be
upgraded to accommodate the greater data and frame size. The Global Diagnostic System (GDS)
will be upgraded to handle ~3X as much real time data as the initial LIGO GDS.
R&D Status/Development Issues
At present, ADC technology is not capable of providing full 20-bit ADC precision at output rates of
16384 samples per second. Our experience indicates that the principal limitation is likely the ADC
board design that uses the 24-bit ADC chip, and we may need to develop in-house or
collaborative solutions with industry to meet our stringent requirements. Additional performance
limitations may also come from the VME format of the boards that initial LIGO uses. The VME
bus is a very noisy environment that may limit ADC performance, and we will study alternatives
such as VXI for sensitive parts of the design.
This will require new solutions to be identified and prototyped to determine performance of
candidate hardware solutions. Using the 40 Meter Interferometer at Caltech, which is designed to
exercise the hardware and software environment for Advanced LIGO, we will perform much of
this type of work.
Similarly, the GDS hardware will need to be scaled for the greater processing and throughput
requirements. Parallelization techniques that are being used in the LDAS I design (e.g., passing
messages across Beowulf clusters) can be introduced to solve compute-bound (but not I/O
bound) data processing problems.
It is plausible that hardware technology trends will continue over the next 5 years. Thus, it is likely
that the solutions required to support the ~3X increased acquisition rates and data volumes would
become commercially available by the time they are needed. We have taken as the point of
departure that “Moore’s law” will be a reasonable predictor of the growth in available
performance.
Work Plan
The first phase will develop a detailed set of requirements for the DAQ upgrade. These will
proceed with the development of a Design Requirements Document and a Conceptual Design.
Activities that begin in this phase include the development and refinement of an Advanced LIGO
model. This will produce a curve of strain sensitivity goal with sufficient details so that issues of
dynamic range, etc. can be addressed with simulation to guide the hardware design. As refined
design information for new SEI, SUS, and ISC subsystems becomes available, the channel count
estimate and their sampling rates will be improved.
The second phase will incorporate results from prototyping. Preliminary board layouts for custom
components will be developed as part of this stage. The procedures by which the existing plant
90
LIGO M030023-00M
will be de-integrated and the newer components introduced will be identified. Software
development associated with DAQ II modifications of the DAQ I plant and infrastructure will begin.
The third phase will culminate in a detailed set of drawings, specifications, and procurement or
fabrication plans for the DAQ II equipment. Fabrication will follow, and it is anticipated that
primarily the LIGO Laboratory staff will carry out this phase as it was during initial LIGO
construction.
91
LIGO M030023-00M
14. Support Equipment (SUP)
Overview
Installation of seismic isolation and suspension subsystems in multiple vacuum chambers at both
sites will require an increase in basic materials handling equipment. These include additional
forklifts, general purpose rigging hardware, personnel lifting devices (of the “Genie-lift” type), and
general-purpose hand tools suitable for use in an ultra-clean environment. Some of this
equipment is also required for assembly of the seismic and suspension units prior to installation.
Functional Requirements
All requirements match those used to select similar equipment for initial LIGO construction.
Concept/Options
There are no significant options in this element.
R&D Status/Development Issues
There are no significant issues in this element.
Work Plan
Procurement of the required support equipment must be completed prior to assembly operations
in 2006, and installation activities in 2007.
92
LIGO M030023-00M
15. Advanced LIGO Construction Project Research and Development
(R&D)
Overview
All identified R&D issues are included in the Advanced R&D program supported by NSF, current
LSC activities, or planned development activities supported within the LIGO Laboratory
Operations budget (WBS 2.0). In general, the separately funded Advanced R&D program brings
all subsystems to the point of the completion of the Design Requirements, the Conceptual
Design, and through significant prototyping. The few exceptions are where no R&D is needed,
and the requirements and conceptual design are very similar to initial LIGO. At present, there are
no activities planned for R&D in the Construction Project phase.
Functional Requirements
TBD
Concept/Options
TBD
R&D Status/Development Issues
TBD
Work Plan
TBD
93
LIGO M030023-00M
16. Data Analysis and Computing Subsystem (COMP)
Overview
The Advanced LIGO data analysis computational load is increased over that for initial LIGO due
to the broader range of detector sensitivity. The features of initial LIGO and Advanced LIGO
sensitivities that impact astrophysical data analysis are summarized inTable 10. The frequency at
optimum sensitivity is fmin= 130 Hz in initial LIGO and roughly at this same frequency (dependent
upon the signal tuning) for Advanced LIGO. However, the Advanced LIGO optimum sensitivity will
be roughly a factor 10 better. The enhanced frequency range for Advanced LIGO means that
sources whose characteristic frequency of emission varies with time will be observable in the
detection band for longer periods. Combined, these enhancements provide both greater range
and in-band dwell times. These improvements imply that the rate of detectable events with
Advanced LIGO will be orders of magnitude greater than initial LIGO. Projected event rate
increases, estimated through scaling laws and anticipated signal signatures, are discussed in the
section 2. Reference Design Baseline Definition, page 1.
Table 10 Key Parameters of the Advanced LIGO Reference Design That Affect the Data
Analysis System
Parameterization
Advanced LIGO
Reference Design
Initial LIGO
Implementation
Comment
Effective Seismic
Cutoff Frequency
fsei ~ 20 Hz
fsei ~ 40 Hz
Point at which
h[fsei] = 10 h[fmin]
Frequency at
Optimum Sensitivity
Fmin ~ 100 -130 Hz
fmin ~ 130 Hz
Minimum of h[f] for
Advanced LIGO is
broader.
h[fmin], Hz-1/2
2-3x10-24
(tuning dependent)
3x10-23
-
Data sample word
length [bytes] for
key channels
4
2
Determined by increased
dynamic range
16384
8192
16384
8192
Maximum Sample
Rate, s/s
fNyquistt, Hz
94
Upper cutoff, fshot, is well
below fNyquistt for both
initial LIGO and II
LIGO M030023-00M
The impact of exploiting the increased source detection ability on data analysis strategies and the
initial LIGO Data Analysis System depends on the source type being considered and will be
discussed by source type below. Most presently envisioned search and analysis strategies
involve spectral-domain analysis and optimal filtering using template filter banks calculated either
from physics principles or parametric representations of phenomenological models. The primary
channel that is useful for astrophysics is the instrumental output that is proportional to strain. All
the other thousands of channels in initial LIGO and Advanced LIGO are used to validate
instrumental behavior. It is also expected that relatively few channels (< 10) will prove useful in
producing improved estimates of GW strain. This would be done by removing instrumental crosschannel couplings, etc. either with linear regression techniques in the time domain (Kalman
filtering) or in the spectral domain (cross-spectrum correlation). We assume here that signal
conditioning will not be a driver for LIGO Data Analysis System (LDAS) upgrades. This is
certainly the case for the initial LIGO LDAS and there is no reason to expect this to change.
Functional Requirements
The most significant new development in distributed computing that has occurred during the
commissioning and operation of LIGO I has been the emergence of the concept of the
Computational Grid. LIGO Laboratory and the LSC are active participants in several NSFsponsored initiatives, with a goal to adopt grid computing methods for the analysis of LIGO data.
The construction of Advanced LIGO offers an opportunity to begin with a new design for the
Advanced LIGO Data Analysis and Computing subsystem that takes full advantage of the grid
paradigm at the time when Advanced LIGO construction starts. This proposal addresses the
LIGO Laboratory Tier 1 components of LIGO data analysis and computing. At appropriate times
in the future, the Laboratory and the LSC will respond to opportunities for funding that will be
needed in order to also enhance the Tier 2 facilities at the collaboration universities. Such
enhancements will include an increase in the number of Tier 2 university centers serving the
LIGO data analysis community.
Computational Upgrades
For the classes of sources considered (transient “bursts”, compact object inspirals, stochastic
backgrounds, and continuous-wave sources), the continuous-wave and binary inspirals place the
greatest demands on the computational requirements. Optimal searches for periodic sources with
unknown EM counterparts (the so-called blind all-sky search) represent computational challenges
that require O[1015 or more FLOPS] and will likely be beyond the capacity of the collaboration to
analyze using LIGO Tier 1 and Tier 2 resources65. Alternative techniques have been developed
that lend themselves to a distributed grid-based deployment. Research in this area has been
ongoing during initial LIGO and will continue. The Tier 1 center upgrade will not be specifically
targeted to this class of search, since it is one that will need to be addressed on a much larger
scale within the national Grid infrastructure.
Advanced LIGO will search for compact object binary inspiral events using the same general
technique that will be employed in initial LIGO: a massive filter bank processing in parallel the
same data stream using optimal filtering techniques in the frequency domain. The extension to
lower frequencies of observation allowed by Advanced LIGO means that the duration of
observation of the inspiral is significantly longer, leading to a concomitant increase in the
computing power required. Counterbalancing this trend, however, are emergent theoretical
improvements in techniques applying hierarchical divide-and-conquer methods to the search
65
c.f., Brady et al., PRD 57 (1998) 2101-2116 and PRD 61 (2000) 082001
95
LIGO M030023-00M
algorithms66. Improvements in search efficiency as high as 100X should be possible by optimal
implementation of these techniques. While not yet demonstrated with actual data, it is reasonable
to expect that algorithmic improvements will become available by the time of Advanced LIGO
turn-on.
The number of distinct templates required in a search depends on many factors, but is dominated
by the low-frequency cutoff of the instrument sensitivity (since compact binaries spend more
orbital cycles at low frequencies) and the low-mass cutoff of the desired astrophysical search
space (since low-mass systems inspiral more slowly, and hence spend more cycles in the LIGO
band). Approximate scaling laws can be used, but in practice the precise number of templates
depends on the specifics of the LIGO noise curve and the template-placement algorithm.
Table 9Error! Reference source not found. provides a comparison between relative
computational costs for inspiral searches down to 1M O• /1MO• binary systems between initial LIGO
and Advanced LIGO. The length of the chirp sets the scale of fast-Fourier transforms (FFTs) that
are required for optimal filtering. FFT computational cost scales as ~N log 2N. On the other hand,
the greater duration of the chirp provides more time to perform the longer calculation. Together a
~7X increase in signal duration corresponds to a ~2X increase in computational cost. If one were
to go to lower mass systems, the computational costs will scale as (Mmin)-8/3. However, current
stellar evolution models predict that the minimum mass of a neutron star remnant is around 1MO• .
Extending the template bank below this limit may be of interest in order to cover all plausible
sources, with a margin to allow for discoveries not predicted by current theories.
When one or both of the binary components are spinning black holes, spin-orbit couplings can
significantly modulate the waveform. Exact theoretical templates for these waveforms do not yet
exist, but would involve several additional search parameters, increasing the size of the template
bank significantly. Buonanno, Chen, and Vallisneri 67 have proposed adopting instead a bank of
approximate templates that uses heuristic waveform parameters (not explicitly tied to the
astrophysical properties of the system) to achieve reasonable overlaps with various competing
theoretical models. A two-parameter template family would be only slightly larger (perhaps by a
factor of 2) than the spinless parameter space, and would have an effective fitting factor (overlap)
of better than 90% with almost all proposed double black hole binary signals. However, it would
match black hole/neutron star signals only at about the 80% level (i.e. 20% loss in signal-to-noise,
or about 50% reduction in event rate). Increasing the fitting factor to above 90% would require
adding a third parameter to the template family, at a significant increase (10X – 100X) in
computational cost compared to non-spinning systems.
At the same time, however, there is much room to improve computational methods to increase
signal-to-noise for fixed computational cost. An 80% fitting factor would be enough for the first
stage of a hierarchical search, which would go on to apply a restricted set of more accurate
templates to candidate events in order to achieve a near-optimal signal-to-noise ratio. As a rough
estimate, we assess a computational cost based on a flat search of a template bank twice as
large as is required for the spinless case, or ~ 200,000 templates.
Each observatory (Hanford, Livingston) has an on-site Linux cluster. The Hanford subsystem of
LDAS handles data from two interferometers and is designed to be twice as capable in terms of
CPU FLOPS as the one at Livingston (some components do not scale and are essentially
identical at both sites). The quantities appearing in Table 9 correspond to the Hanford site
operating with two interferometers.
Table 10 lists the main features of the parallel cluster at Hanford.
66
67
Dhurandhar et al., gr-qc/030101025, PRD 64 (2001) 042004
gr-qc/0211087
96
LIGO M030023-00M
Table 9 Initial LIGO and Advanced LIGO Analysis System Requirements for compact
object binary inspiral detection using Wiener filtering techniques. M=1MO• provides a
reference to indicate how quantities change with Mmin. Quantities were calculated using
a spreadsheet model of the data flow for the inspiral detection analysis pipeline, and
assume a 20 Hz start frequency for observation.
Parameter
Advanced LIGO
(LHO, 2 IFOs)
Initial LIGO
(LHO, 2 IFOs)
1MO• /1MO•
1MO• /1M
Maximum template
length, seconds
280 s
44 s
Maximum template
length, Bytes
128 MB
16 MB
Number of templates
2.5 x 105
1.3 x 105
Calculation of
templates, FLOPS
~4
GFLOPS
~2
GFLOPS
Storage of templates,
Bytes
32 TB
2 TB
Wiener filtering
analysis, FLOPS
(flat search)
4970
GFLOPS
440
GFLOPS
Table 10 Initial LIGO and Advanced LIGO Analysis System Specification for compact
object binary inspiral detection using Wiener filtering techniques.
Parameter
Beowulf Cluster Size
(# nodes @ LHO)
Memory per CPU, MB
Disk per node, GB
GHz per node
Total Computational
Power, GHz
Advanced LIGO
256
Initial LIGO
96
1024
60
>3
>768
512
20
2.1
200
The off-site computing facilities at Caltech support network analysis for follow-up analyses
requiring data from all three interferometers. In addition the computational facility will support Tier
1 functions of data storage and retrieval functions. The parallel Beowulf cluster at Caltech will
also be upgraded to provide expanded search and analysis capacity. The Caltech Beowulf cluster
has been estimated to require of order 512 nodes. Similar scaling of the smaller computational
facility at MIT will be undertaken.
Data Archival/Storage Upgrades
The Advanced LIGO acquisition system will generate a ~3X greater volume of data that needs to
be accommodated by the archive and on-line mass storage systems (as explained in Section 13.
Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ), page 1). At the present time
it is not clear the degree to which the additional data associated with monitoring functions of
instrumental performance needs to be accessed by the collaboration for science and detector
97
LIGO M030023-00M
characterization functions. However, experience to date with LIGO I has shown that any data that
are acquired are required to be archived indefinitely. We will use this same data model as a
conservative estimate for Advanced LIGO requirements. In this model, all data are acquired and
stored for several weeks on-line in a disk cache at the observatories. Then the data are staged to
tape media. Two copies of tapes are produced. One copy is held on-site for ~30 days. The other
copy is sent to Caltech where data reduction takes place in the form of keeping only those
channels that are required for data analysis on Reduced Data Sets (RDSs). The target in initial
LIGO will be a 10X reduction in raw data volume for the RDSs. We expect ~3X to come from
lossless compression (both in hardware within the tape drives and algorithmically in filters).
Another ~3X will come from re-sampling and reduction in the number of channels. The net result
is a need to upgrade the permanent archive; Advanced LIGO will require a ~ 1PB/yr archive
capacity.
Handling Greater DAQ Data Rates – Frame Data Archive Growth
Data from the interferometer and PEM subsystems will be accommodated for periods of 3 weeks
hours on spinning media. The corresponding volume of data that must be accommodated is ~10
TB. The on-site disk cache for Advanced LIGO will require expansion to 20 TB. This volume
represents ~100% margin for additional growth, which is comparable to the initial LIGO design.
Handling Greater Event Rates – Metadatabase Growth
The LIGO metadatabase serves to provide logging of diagnostics triggers that come from realtime monitoring of the interferometer and PEM channel, and to provide for logging of frame data
and candidate astrophysical events. Depending on the levels of compression that are ultimately
achieved on the raw framed data, metadata generated from frames (trends, histories, etc.) will
grow directly as the volume of frames. If this is assumed to grow by ~3X, then Advanced LIGO
will require an increase of 3X in storage and serving capacity for frame summary metadata at the
Caltech server.
Wide Area and Local Area Network Upgrades
The increased volume of data generated can be expected to generate a concomitant need to
provide increased internet connectivity between the observatories and Caltech and in general to
the larger LSC community. At the present time, LIGO Laboratory has not been able to obtain OC3
connection to the internet at the observatories due to costs that cannot be absorbed by the
operations budget of the Laboratory. By the time of Advanced LIGO, the Laboratory will require
an upgrade to at least OC3 to provide to LIGO Laboratory adequate bandwidth between
observatories and Caltech.
Software Upgrades
The data analysis software will need to be grid-enabled as part of the upgrade in support of
Advanced LIGO. In some cases, certain interfaces may need to be expanded to accommodate
the greater level of distributed computing being foreseen. It is expected that the research results
provided by other NSF-funded grid computing projects in which LIGO Laboratory and the LSC is
actively participating will provide the guidance of how this evolution will take place.
Another large impact to LDAS software design will be in the area of database management
systems to handle the greater quantity of data and a growing community of users. Advanced
LIGO will require a greater database size, more powerful and more numerous servers, and a fully
federated implementation of the database system.
98
LIGO M030023-00M
Concept/Options
The implementation of Advanced LIGO LDAS is an expansion of initial LIGO LDAS. This is
largely possible because of the highly modular, API-specific, object-oriented paradigm that initial
LIGO is implementing. The desire to enable a greater degree of integration into a grid computing
paradigm than has been possible for LIGO I will determine the evolution of LDAS in support of
Advanced LIGO.
Additional PC clusters will be added to or replace existing clusters. LAN network infrastructure in
place for initial LIGO will be capable of expansion to accommodate 4X bandwidths by
combinations of multiple connections (e.g., an increased number of network fabrics) and higher
bandwidth (OC12 or OC48). The RAID disk systems planned for initial LIGO will be expanded or
replaced with improved versions of similar systems (later generation, larger disk volumes, etc.).
These disk systems will support growth of both metadatabases and framed databases. Data
servers will be upgraded to the enterprise class servers available at the time. Multiple servers
may be clustered to provide greater throughput where this is required.
Tape archive robotic systems will be upgraded or replaced. The growth of the local short-term
archives at the observatories will be possible using the LIGO I SAM-QFS or a similar software
environment on the archive server at the sites. Such products are licensed based on data
volumes, so as the archives at the observatories grow, the net operational costs will be
proportionately increased. The Caltech archive shall be expanded to accommodate the greater
volume of Advanced LIGO data.
WAN access to LIGO data will be provided from each observatory and Caltech at OC3 or greater
bandwidth.
R&D Status/Development Issues
Most of the improvements in hardware performance that are discussed and identified above
should become naturally available through the advance in technology that comes from market
forces. LIGO will continue to meet its needs using commercial or commodity components.
Software evolution towards a grid-based paradigm will occur through continued participation by
the Laboratory and the LSC in NSF-funded grid computing initiatives.
99
LIGO M030023-00M
Work Plan
A Design Requirements and Conceptual Design Review (DRR) will take place once the key
functional requirements have been identified. The conceptual implementation is designed to
develop a credible basis on which the upgrades can be planned and built. It also serves to firm up
projected budgets and to identify any design changes that were unforeseen at the time of the
proposal. This review should take place within the first year of inception of LDAS II work.
Based upon initial LIGO experience, a Preliminary Design Review (PDR) will take place
approximately one year after the DRR. The concept described in the DRR is “fleshed out” to the
point where it is reasonably certain that there are no “show stoppers” in the proposed
implementation approach. Hardware solutions are identified; software implementations are
prototyped; prototyping results for computational costs, data access times, storage volumes, etc.
will generally become available during and immediately after this review stage.
A Final Design Review will take place approximately one year after the PDR. At this point, the
detailed procurements list and design for how each of the upgrades takes place will be
completed. Plans will be developed for how LDAS I components will be decommissioned and
replaced with Advanced LIGO components from initial prototypes through to the operational
systems. After this juncture, complete implementation will begin and continue for 1 – 2 years.
100
LIGO M030023-00M
17. Installation and Commissioning Task (INS)
Overview
The installation and commissioning of the Advanced LIGO detector systems is planned to be as
rapid as possible in order to minimize the observatory downtime. It requires the installation of all
detector elements in all three LIGO interferometers in a phased approach to best utilize the
infrastructure and manpower in the Laboratory and LSC. The subsystem teams are expected to
have pre-assembled and pre-tested components available for installation when needed (some
assembly and test can take place at the observatory sites in advance).
Functional Requirements
At the end of the installation and commissioning period Advanced LIGO should be running
reliably near design sensitivity. The installation and commissioning effort must be done
simultaneously with continued observatory site and LIGO Laboratory operations, though much of
the staff will be diverted to installation and commissioning tasks.
Concept/Options
The basic conceptual plan for the installation is as follows:








The installation and commissioning phase is under the direction and responsibility of the
LIGO Laboratory. LSC members may contribute and assist. We assume that developers
of technology in the LSC will participate in installation and commissioning of their
respective components, though our planning assumes much of the labor required will
come from the Laboratory staff or contractors.
Full-scale subsystem testing is performed to prove out the design and fabrication of
components, assemblies and subsystems and their interfaces wherever possible.
System level testing of the full configuration (power and signal recycled Michelson with
Fabry-Perot arm cavities) with as much of the full-scale hardware as possible (active
seismic system, suspension system, etc.) is performed on the Caltech 40 Meter
Interferometer and MIT LASTI testbeds.
Installation exercises will be carried out for the major mechanical subsystems at the MIT
LASTI testbed, training the subsystem and observatory staff who will then carry our the
installation at the observatories.
Pre-assembly, pre-alignment and pre-testing (to the extent possible) is carried out for all
subsystems prior to installation into the system. For example, the seismic systems will be
fully preassembled and sealed for transport from onsite staging buildings into the vacuum
equipment areas. Suspensions will be preassembled onsite up to attachment of the final
silica fibers and test masses. These will be installed at the time the vacuum system is
ready to receive the subsystems.
In order to minimize observatory downtime, installation will not begin until all required
fabrication is complete and all required assembly and unit level testing is complete.
Two shifts of installation are planned only for labor-intensive activities on the critical path
and held in reserve for contingency for non-critical tasks.
The commissioning teams, as in initial LIGO, require expertise from multiple disciplines
and subsystems. Staffing for the design and development phases of the Advanced LIGO
effort are planned with the intent of providing this expertise.
One possible option in the overall program, which has significant impact on the installation and
commissioning phase, is whether the initial LIGO 2 km interferometer is converted to a 4-km
101
LIGO M030023-00M
interferometer or operated in the initial LIGO configuration. The baseline for this proposal is that
the 2km interferometer will be upgraded and the arm length will be extended to 4 km.
R&D Status/Development Issues
A rapid and predictable installation schedule requires well thought out and tested installation
procedures and fixtures. LASTI will provide an opportunity to test these installation procedures in
full-scale chambers and to train team leaders. This development is essential for successful
installation of the interferometers.
System R&D and testing of the signal and power recycled configuration on the 40 Meter testbed
is essential for the commissioning team to gain the experience and expertise that will be required.
Work Plan
In early 2007, the three initial LIGO interferometers will complete their coincident observation run
and the Livingston instrument will be turned off. This event will trigger the start of installation
activities. For many months prior to this point, the subsystem components will have been prepositioned at the sites, assembled and tested, and the limiting pace should be set by the available
skilled manpower. Near the end of 2007, the initial LIGO Hanford instruments will be turned off.
The seismic isolation installation will be completed at Livingston by that time, and that installation
team will migrate to Hanford for the commencement of installation there. This staggered pattern
will continue with the suspensions, optics, and the other subsystems.
This is the baseline plan. The status of the global observing networks, agreements between
projects, and scientific and technical developments may motivate altering the order of upgraded
interferometers or the interval between installations of the successive interferometers.
The plan is to perform the physical installation as rapidly as possible to maximize the time for
debugging, characterization and commissioning. This is enabled by the pre-deployment of all
materials to the sites and by the full-scale testing which minimizes the risk of rework.
The top-down schedule is shown in Figure 26.
102
LIGO M030023-00M
Figure 26 Top Level Advanced LIGO installation Schedule68
68
Based on the Advanced LIGO project schedule, LIGO M020121-D
103
LIGO M030023-00M
18. Project Management (PM)
Overview
The Advanced LIGO Project Office will be organized in the same way as for initial LIGO
construction69. The principal difference is that some functions will be supported by the LIGO
Laboratory operations budget (WBS 2.0). Only the incremental and specific Advanced LIGO
tasks will be supported from this element of the Advanced LIGO WBS.
Functional Requirements
Advanced LIGO Project Management must provide a means of managing project performance
with an earned value system, and maintaining control of the Advanced LIGO configuration and
baseline. It must provide project reporting, manage project procurements, safety, quality
assurance, provide definition and support of the technical system configuration and interfaces,
and support general computing, document control and information systems.
Concept/Options
The management concept is the same as the initial LIGO technique and this will be described in
an Advanced LIGO Project Management Plan. The Advanced LIGO Project Management Plan
will be substantially similar to the Plan used during initial LIGO construction.
R&D Status/Development Issues
There are no development issues or R&D for this WBS element.
Work Plan
An Advanced LIGO Project Office will be organized and will manage the presently ongoing preconstruction R&D as well as the fabrication and construction phase proposed here. It will be part
of the LIGO Laboratory. It will rely on some services provided by the LIGO Laboratory Directorate
and Business Group and will contain the incremental tasks required by Advanced LIGO
construction.
69
LIGO Project Management Plan, LIGO M950001-C-M.
104
LIGO M030023-00M
19. Schedule
Advanced R&D Summary Schedule
The Laboratory maintains the Advanced R&D Summary Schedule 70. The Advanced LIGO
construction project Summary Schedule below has been coordinated with that schedule.
Advanced LIGO Summary Schedule
Milestones for potentially critical path Advanced LIGO activities are listed in Table 11. These
milestones are coordinated with the development schedule.
70
Advanced R&D Schedule, LIGO M020121
105
LIGO M030023-00M
Table 11 Advanced LIGO Construction/Installation Summary Milestones
Milestone
NSF Early Funding for Core Optics Available
NSF Funding for Advanced LIGO Construction Available
Vacuum Equipment Contract Placed
Vacuum Equipment Ready to Install
Clean Rooms Contract Placed
Clean Rooms Available for Staging Areas
Clean Rooms Available for Vacuum Equipment Areas
Seismic Isolation Final Design Review
Seismic Isolation Assembly Started
Seismic Isolation Ready for Installation
Suspension Subsystem Final Design Review
Suspension Subsystem First Articles
Suspension Subsystem ready for Installation
Pre-stabilized Laser Final Design Review
Pre-stabilized Laser ready for Installation
Core Optics Components Final Design Review
Core Optics Components First Articles Available for Suspension
Interferometer Sensing and Control Final Design Review
Installation begins at Livingston
Installation begins at Hanford
Commissioning begins at Livingston
Commissioning begins at Hanford
Livingston Operational
Hanford Operational
Date at End of Quarter Per
Calendar Year
1 Apr 2004
1 Apr 2005
26 May 2005
10 Nov 2006
1 Apr 2005
2 Feb 2006
8 Mar 2007
17 Nov 2004
11 Nov 2005
17 Aug 2006
8 Mar 2006
15 Nov 2006
2 May 2007
17 Aug 2005
2 Nov 2006
27 Apr 2004
2 Mar 2006
16 July 2005
8 Mar 2007
15 Nov 2007
21 Sep 2007
29 May 2008
4 Mar 2009
6 Jan 2010
Relationship to Laboratory initial LIGO and Operations Schedule
Initial LIGO scientific operations will continue during 2007. Through 2006, LIGO Laboratory staff
supported under the existing Cooperative Agreement will be carrying out the portions of the LSC
R&D program related to Advanced LIGO. Advanced LIGO construction funds will support
incremental staff required to carry out Advanced LIGO design, fabrication and assembly.
Following shutdown of the initial LIGO detector systems, a significant portion of the LIGO
Laboratory staff becomes available to support Advanced LIGO installation and commissioning. In
addition, incremental contractor staff will be added to support installation. These contractors are
budgeted in the Advanced LIGO construction estimate.
Participating LSC members from outside the LIGO Laboratory are expected to support installation
and commissioning of the LIGO systems.
106
LIGO M030023-00M
20. Cost Estimate
Methodology for this estimate
The cost estimate developed for this proposal was performed at the lowest feasible level, given
the present level of development in the WBS, in a bottom-up manner. Most subsystems have
been costed at a level of detail comparable to initial LIGO; several have not achieved the maturity
in R&D to allow this level of detail, but carry contingency appropriate to the basis. The techniques
used were the same methods used to estimate initial LIGO construction costs, though our cost
experience in initial LIGO substantially improved the input knowledge base for the new estimate.
Contingency was estimated using the formal graded approach to assessing technical, cost and
schedule risk that was used in initial LIGO.
Estimate summary table by WBS
In FY XXXX US$ (non-escalated), we have made a cost estimate for the Advanced LIGO
reference design. By subsystem, these estimates are summarized in Table 12.
Table 12 Advanced LIGO Cost Estimate Summary
WBS
Subsystem
Estimate
(FY 2003 K$)
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.12
4.13
4.14
4.0
Facility Modifications (FAC)
Seismic Isolation Subsystem (SEI)
Suspension Subsystem (SUS)
Prestabilized Laser Subsystem (PSL)
Input Optics Subsystem (IO)
Core Optics Components (COC)
Auxiliary Optics Subsystem (AOS)
Interferometer Sensing and Controls Subsystem (ISC)
Data Acquisition and Diagnostics Subsystem (DAQ)
Support Equipment (SUP)
Data Analysis and Computing (COMP)
Installation and Commissioning (INS)
Project Management (PM)
Advanced LIGO Construction and Installation Total
This estimate is based on the reference design scope that has been chosen to include the
preferred options in most choices where alternates exist. These include the choice to upgrade all
three interferometers, to increase the arm length of the short initial LIGO interferometer, and to
optimize performance for the significant technical options.
The costs in Table 12 do not include the R&D, and the technical and administrative support,
already proposed in the existing Cooperative Agreement.
The GEO Project has proposed to provide a capital investment in this construction project. These
capital investments are separately proposed by the UK and German parts of the GEO Project.
107
LIGO M030023-00M
The GEO UK proposal is for approximately $11.5 million43,71. They propose to apply these
resources to providing the suspension subsystem, including suspension assemblies, their
controls, and installation and commissioning. This is a particularly appropriate contribution to
Advanced LIGO as the suspension subsystem is based upon the GEO Project implementation for
the GEO 600 interferometer.
The GEO German proposal is for the design and fabrication of the pre-stabilized laser (PSL)
subsystem. This includes the power laser, the reference and pre-mode cleaner cavities, and the
control systems for the pre-stabilized laser, and covers complete PSL units for the subsystem and
system testing as well as PSL units for the observatories. The German GEO group has produced
the laser for GEO-600 and has a great deal of experience in this domain. The amount of the
contribution is expected to be approximately $11.5 million72
The Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) also proposes a
significant role in Advanced LIGO R&D, construction and implementation. The Australian
proposal is for approximately $2.9 million, and will support the baseline output mode filtering
system and R&D to develop a variable transmission signal recycling mirror as a powerful
enhancement to Advanced LIGO.
With the GEO and ACIGA capital contributions, the requested US Advanced LIGO costs are $
XXXXX K in FY 2003 $. Escalating this sum to the planned project schedule yields a total request
to the NSF of $ XXXXX K.
Should the GEO or ACIGA capital contribution not materialize in full, the Advanced LIGO
implementation will be de-scoped to control the request to assure that the final requested funding
is less than or equal to the estimate above.
Cost Drivers
Significant cost drivers in the Advanced LIGO estimate include:












Upgrading of three interferometers
Rapid and closely sequential assembly and installation
Use of isolation systems with multiple actively controlled degrees of freedom
Use of multiple pendulum suspensions with additional stages and active controls
Stringent isolation requirements for smaller optics
Higher power lasers requiring expensive laser diodes and thermal control measures
Large core optics of either sapphire or fused silica (comparable cost)
High count of control loops
High channel count for diagnostic channels
Increased detector sensitivity and bandwidth
Greater data storage needs
Greater communications bandwidth needs
Risk Areas and Contingency
Contingency has been estimated for each subsystem based upon top-level estimates by
subsystem. Of the total estimate above, contingency funds have been estimated to be $ XXXXX
K. The estimate is substantially based upon well-known unit costs. Great conservatism has been
used in carrying out the estimate, and most subsystems have potential for de-scoping. The
combination of established unit costs and labor rates, and the large scope contingency support
71
72
Private communication, J. Hough, 8 January 2003
Private communication, K. Danzmann, 29 January 2003
108
LIGO M030023-00M
this estimate. If decisions are made to reduce scope, funds will be added to the contingency pool
to offset the scope contingency.
Funding Profile
A working funding profile has been calculated which enables the planned schedule. We note that
long-lead-time procurements such as the purchase of vacuum equipment components, and
purchase of large optics substrates, will define early funding needs.
109
LIGO M030023-00M
21. Responsibilities/Resources/Staffing
Method of Organizing Non-Laboratory Participation (LSC, MOUs,
Attachments, Subcontracts)
As discussed in the section on the LIGO Laboratory Role and Responsibilities and the LIGO
Scientific Collaboration Role and Responsibilities, the LIGO Laboratory will manage the execution
of the Advanced LIGO Project. Non-Laboratory participants will be involved in the construction
through written Memoranda of Understanding (MOU) and specific Attachments defining
resources, responsibilities, deliverables and milestones. Where appropriate, activities will be
supported by subcontracts placed by the LIGO Laboratory.
Subsystems and Institutional Roles
Institutional roles in the design and fabrication of subsystems will be -documented in the
Advanced LIGO Project Management Plan, and in associated MOU’s and Attachments. The
present state is outlined below.
GEO Participation
The GEO Project is operating a 600-meter interferometer in Germany with several advanced
technologies. This instrument employs signal recycling, though in a delay line arm configuration,
and multiple pendulum suspensions of advanced design. They are proposing to collaborate with
the LIGO Laboratory in the construction and exploitation of Advanced LIGO. The GEO groups are
members of the LSC and are participants in the LSC research and development program leading
to Advanced LIGO.
GEO proposes to participate in Advanced LIGO suspensions and sapphire core optics, in the
development of the signal recycling, and in the pre-stabilized laser subsystem for Advanced
LIGO.
For the suspension subsystem, GEO proposes the following roles:




GEO would lead the design and take part in the prototyping of the multiple pendulum
suspensions with silica and sapphire bottom stages for the Advanced LIGO system. This
activity would be carried out under the advanced R&D phase of the program
After this prototyping, GEO would participate in testing in the MIT LASTI system. This
activity would be carried out under the advanced R&D phase of the program and would
take place prior to construction of the first article suspension. This subsequent
construction would not be the responsibility of the GEO group.
The GEO group proposes to have joint responsibility with the LIGO Laboratory for the
installation and shakedown of the suspension systems.
Subject to funding agency approval, GEO would support the funding for construction and
installation of the Advanced LIGO suspensions and controls and would supply a number
of the sapphire test mass substrates.
For the signal-recycling task, GEO proposes the following roles:


GEO would take a leading part in the research and development of signal recycling
system for Advanced LIGO. This activity would be carried out under the advanced R&D
phase of the program.
GEO proposes to have joint responsibility with the LIGO Laboratory for installation and
shakedown of the signal recycled Advanced LIGO interferometers.
110
LIGO M030023-00M
For the pre-stabilized laser subsystem, GEO proposes the following roles:



GEO would take a leading part in the identification of the approach to the high-power
laser head, and consequently the integration of the selected head with the stabilization
system. This activity would be carried out under the advanced R&D phase of the
program.
Subject to funding agency approval, GEO would support the funding for construction and
installation of the Advanced LIGO pre-stabilized lasers
GEO proposes to have joint responsibility with the LIGO Laboratory for installation and
shakedown of the pre-stabilized laser subsystems.
GEO is making a proposal for a capital contribution to Advanced LIGO. They are at the final
stages of approval for a proposal to the UK Particle Physics and Astronomy Research Council for
a large part of the suspension subsystem and for part of the core optics. A companion proposal
for provision of the laser system is about to be submitted to the relevant German funding
authority. With approval of these initiatives by the respective funding agencies, and agreements
contained in MOUs and specific Attachments, the GEO groups will become partners in the
leadership and execution of the Advanced LIGO project.
ACIGA Participation
The ACIGA Consortium is pursuing research in a broad range of activities relating to
interferometric gravitational wave detection. They have a number of laboratories, including the
Gingin facility allowing interferometric tests over an 80m baseline. They are proposing to
collaborate with the LIGO Laboratory in the construction and exploitation of Advanced LIGO. The
ACIGA groups are members of the LSC and are participants in the LSC research and
development program leading to Advanced LIGO.
ACIGA proposes to participate in the Advanced LIGO Thermal Compensation effort and to
investigate the addition of a variable signal-recycling mirror to the Advanced LIGO baseline. They
also wish to contribute the output mode cleaner for one of the interferometer systems.
Discussions are underway to refine the proposal, with the objective of establishing an MOU and
attachments relevant to the contribution.
111
LIGO M030023-00M
Education and Outreach From the LSC
Broader Impacts of Advanced LIGO
Advanced LIGO is the proposed goal of the entire LSC, including more than 38 institutions and
470 members globally. In this light, implementing Advanced LIGO should be used as an
opportunity to join the separate LSC education and outreach activities of member institutions into
a coordinated and networked program. The broader impacts of the LIGO Laboratory and the LSC
will be developed into a mutually supportive program, fully leveraging the facilities, resources and
capabilities of the LIGO community to reach the broadest audience.
Other LIGO Outreach Activities
The LIGO Laboratory has engaged in significant education and outreach during the mature
phases of LIGO construction. These activities have generally been centered near our observatory
sites where LIGO is able to have the most immediate and tangible impact73.
This program has continued during the operations phase under the new Cooperative Agreement
as described in this proposal in the section Outreach. The Laboratory has begun to add staff
support and has formed local educator networks (LEN) about each observatory. These networks
have initiated a new program plan for observatory-based outreach. Additional staff will be added
to the observatory-based outreach programs to support the additional scope.
The Laboratory is also submitting a new proposal74 based upon the work of the two LENs, to the
NSF IPSE program. That proposal addresses new initiatives in formal and informal science
education, and the creation of the civil infrastructure in Louisiana to support the expanded
program. It has been discussed with NSF and guidance received has been considered in forming
the LIGO proposals. The proposal is a three-year proposal for FY2004 through FY2006.
Continuation of the activities of that proposal would be included in the LIGO Laboratory proposal
to continue operations in FY2007 through FY2011.
Similarly, a plan is emerging for production of an educational film about LIGO. This is under
discussion with NSF. The goal for this film is to reach audiences from high school students, to
educated members of the public, visitors to the LIGO observatories, and the public television
audience. This is part of the LIGO Laboratory strategy to begin to address broader national
audiences as we build mature programs on a regional or local basis. This first step, a LIGO
documentary, should be completed in FY2004.
The LSC Outreach Program
The LSC Executive Committee has endorsed the formation of a coordinated LSC education and
outreach program. As an LSC effort, the Advanced LIGO construction project provides the
inspiration. The separate efforts of the 38 institutions in the LSC will be leveraged to produce this
new thrust.
73
LIGO NSF Proposal for Continuing Operations 2002-2006 (Dec 2000), pgs 24, 84, 165,
http://www.ligo.caltech.edu/docs/M/M000352-00.pdf
74 NSF Proposal PHY-0324802, The Laser Interferometer Gravitational-Wave Observatory (LIGO)
Local Educational Outreach Partnership, LIGO-M030027-00-M
112
LIGO M030023-00M
In addition to leveraging the disparate programs, this is an opportunity to advance LIGO-related
outreach from the character of an “add-on” to basic research programs to a world-class education
and outreach activity in itself. A great deal has been accomplished in the last decade in bringing
broader impacts into the vision of the NSF supported research community. The public’s
investment in frontier research has been exploited to provide excitement, education and
knowledge to the public. But the creation of so many individual outreach efforts by scientists
expert principally in their own fields has not always been able to match the excellence of the
basic scientific research itself. LIGO hopes to develop an outreach program that fully matches the
excellence of LIGO scientific research in quality. In order to accomplish this, we propose to
combine our individual collaborating team resources with the leadership of a world-class expert in
science, technology, engineering, and mathematics (STEM) education. LIGO and the LSC would
be the home for a program led by this individual.
We propose to recruit the leadership needed and to survey, design and found the LIGO/LSC
education and outreach program during the period of Advanced LIGO construction. Future
operating awards would support the program that would be developed for the LIGO Laboratory
and LSC institutions as appropriate to the detailed program.
Since the earliest construction-related funds requested in this proposal are scheduled for
FY2004, we propose to commence the LSC outreach program development in FY2004. The
resulting program should be in place by the end of FY2006 when the LIGO Laboratory should
begin support in a new operating award that would sustain the developed program.
The development of the program will follow the steps:
o
o
o
o
o
o
o
o
o
FY2004 – Recruit LSC Outreach Director and assistant
FY2004 – Survey all LSC education and outreach activities and develop a descriptive
survey document
FY2004 – Formation of LSC Educators Advisory Network
FY2004 – August 2004 LSC meeting is used to host an additional two day LSC Outreach
Workshop at which all LSC activities will be showcased and attendees, including outside
consultants and advisory network members will participate in design discussions for an
enhanced, coordinated LSC program
FY2005 – LSC Outreach Director develops detailed program plan with review meetings
and educators advisory network participation
FY2005 – March 2005 LSC meeting hosts one day LSC Outreach Workshop to finalize
and approve program plan
FY2005 – Initial elements of the plan implemented
FY2005 – Supplemental proposals to NSF are submitted as necessary
FY2006 – Initial operation of the coordinated LSC outreach programs
The developed program will include all elements of the existing LIGO Laboratory outreach
program. The LSC Outreach Director will assume overall responsibility for these and for new
program elements. The Director will also coordinate the efforts of the LSC institutions through
governance mechanisms established by the LSC. A formal program management plan and
appropriate Memoranda of Understanding (MOUs) will be employed to establish the governance,
responsibility and accountability.
113