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AStroParticle ERAnet
Implementation of Astroparticle
Physics European Coordination
Period covered: 1st July 2006 – TU+VMZ
Start date of project: TUKVMZ%VSBUJPONPOUIT
Project coordinator name: 4UBWSPT,"54"/&7"4
Project coordinator organisation name: $/34$FOUSF/BUJPOBMEFMB3FDIFSDIF4DJFOUJGRVF
$PQZSJHIUª-#SFU/PWBQJYt"MMSJHIUTSFTFSWFE"41&3"
D2.2 - R&D for
Astroparticle Physics
Abstract
There are recurring characteristics of Astroparticle Physics observatories: the detection of extremely rare cosmic ray events or of rare processes inside cryogenic
crystals, special isotopes or radiopure liquids. One also need to detect gravitational waves using state of the art optical systems. In order to achieve the above, one
needs to instrument large areas or volumes with detectors in sometime hostile environments, or deploy sensitive detectors underground, in order to avoid radioactive backgrounds from cosmic rays or the environment. One further needs facilities
for developing radiopure materials with special characteristics. Many applications in
Astroparticle Physics require new types of electronics developments, for fast lowcost integrated signal acquisition, and/or for autonomous distributed «smart» dataacquisition. As a result of the above characteristics, most of the techniques used
in Astroparticle Physics have possible applications in climate and risk monitoring
as well as biomedical imaging. In the following we analyse the detector elements,
materials, electronics and examples of applications of Astroparticle Physics R&D.
R&D for Astroparticle Physics
CONTENTS
I. Detector elements for Astroparticle Physics
1.1. Photodetectors for HEAP and large underground detectors................................ 4
1.2. Cryodetectors...................................................................................................... 6
1.3. Optical elements, lasers and suspensions for gravitational wave antennas........ 8
1.4. Astroparticle Physics detectors in space............................................................ 12
1.5. Distributed electronic and acquisition systems for Astroparticle Physics........ 15
1.6. Fast and low-cost front-end read-out systems for Astroparticle Physics............. 16
II. Materials for Astroparticle Physics
2.1. Noble liquids for dark matter and double beta decay......................................... 19
2.2. Scintillators for neutrino physics and proton decay............................................ 22
2.3. Analysis on rare isotope preparation for Astroparticle Physics.........................
23
III. New techniques for Astroparticle Physics
3.1. Radiodetection.................................................................................................... 29
3.2. Acoustic detection of Ultra High Energy (UHE) neutrinos................................ 33
3.3. Gas TPC technology R&D................................................................................
37
IV. Technologies from Astroparticle Physics for the monitoring
of the environment and risk prevention...................................................................... 41
V. Credits.................................................................................................................... 49
I
DETECTOR ELEMENTS FOR
ASTROPARTICLE PHYSICS
Dectector elements for Astroparticle Physics
1.1. Photodetectors for HEAP and large underground
detectors
Observing high-energy cosmic radiation bears an enormous potential for making
scientific breakthrough discoveries. This has been proven by the present generation
instruments, like Auger-South, HESS and MAGIC. The photodetector is a basic and
critical building block for nearly all experiments in the field of Astroparticle Physics.
In particular, observatories detecting high energy cosmic radiation such as gamma
rays, neutrinos, and charged particles, all use techniques based on measuring Cherenkov or fluorescence light induced by particle showers in different media: atmosphere, water or ice.
Next-generation instruments, like CTA and Auger-North will require a substantial
increase in size, and the individual detectors must reach the highest possible sensitivity. Detectors will also consist of a much larger number of photodetectors. New
advanced photodetectors with new technologies, which are cost effective and have a
much improved performance are desired for the next generation experiments. Some
of the projected developments are developed below:
UV sensitive SiPMs and array of SiPMs.
The SiPM (Silicon photomultiplier) is a novel photodetector consisting of a huge
array of Si-APDs working in limited Geiger mode. This is a unique solid state photodetector, which can be used in single photon counting mode. Currently, SiPMs with
a size from 1mm x 1mm to 5mm x 5mm are available. Recently there have been
some activities to produce arrays of SiPMs to obtain a larger acceptance area with
a small dead space, or to obtain position sensitive devices. The photodetection
efficiency is still in the range of 15-50%. Most of the devices are produced with a
n-on-p structure, and the urgent development of a p-on-n structure is necessary
for achieving higher sensitivity in UV and blue wavelength. The developments
will be twofold. One is the development and improvement of the device itself.
This development will provide the SiPMs and the array of SiPMs which satisfy our
requirements in high energy Astroparticle Physics experiments. The other is the
application level developments and the demonstration in the field using an existing
telescope.
In particular what concerns the development of the device itself we need
•
Develope UV sensitive SiPMs with high photodetection efficiency of 60% or higher
•
Fabricate several types of SiPMs up to a size of 25 mm 2
•
Fabricate several types of buttable 4 x 4 arrays or 4 x 16 arrays of SiPMs as modules
And in what concerns the application we need to:
•
Standardize the cooling unit, biasing circuits and cooling method for
SiPM arrays
•
Demonstrate gamma ray observations with a SiPM camera of 256ch using an existing telescope or an old last generation telescope
4.
Dectector elements for Astroparticle Physics
GaAsP photocathode HPDs.
The development of the high quantum efficiency (Q.E.) Hybrid Photon Detector
(HPDs) and its demonstration in an existing imaging atmospheric Cherenkov
telescope are proposed. Recently, the MPI-Munich group in collaboration with the
company HPK succeeded in developing 18mm size HPDs of 55% Q.E. with a
GaAsP photocathode. The aims of the development are optimizing the spectral
response (enhance the blue colour sensitivity) to fit Cherenkov / fluorescence light
observation, and improving the time resolution to ~2nsec (FWHM) for single photo
electrons. In parallel, the GaAsP window will be optimised in order to achieve
a lifetime which is sufficient for 10 years of operation in the realistic night sky
background environment. The MAGIC-II telescope is scheduled to be upgraded
with this type of HPDs.
Improvement of PMTs for Gamma Ray and Neutrino astronomy.
The photomultiplier (PMT) has a long history and was considered a matured device.
The quantum efficiencies (Q.E.) of PMTs amounted to 20-30% for a long time.
However, recently there was a breakthrough in photocathode process technology,
and this new technology allows us to reach a high quantum efficiency of about 45%.
The cost of this new process is not so expensive. The current problem is
that such kind of technology was applied only with limited types of PMTs.
We need to:
•
•
Improve the photocathode for several PMTs with a size from 1” to 2” and boost further the quantum efficiency for ground-based gamma ray
astronomy.
Improve the large hemispherical PMTs, which can be used in experiments
for high energy neutrinos and ultra high energy cosmic rays.
The improvement s hall be done in several parameters, Q.E., time and charge resolutions, dynamic range, and low after-pulse rate, etc.
For high energy neutrino experiments, studies and the development of the following items are encouraged:
Photodetector module with a cluster of medium size high Q.E. PMTs
Directional sensitive large hemispherical multi-anode PMTs
High photo-collection efficiency X-HPDs
•
•
•
Recommendations and conclusions
In summary, we need to develop advanced photodetectors for the next generation of detectors for Astroparticle Physics research in order to conserve
and enhance the current European leadership and to collaborate within the
development projects with European companies, transfer technologies and
encourage or initiate the production of new photodetectors.
Contact: M.Teshima, [email protected]
5.
Dectector elements for Astroparticle Physics
1.2. Cryodetectors
Credit: Max-Planck-Institut für Physik, Muenchen High purity CaWO4 crystals under UV illumination
used for the CRESST Dark matter experiment.
The present Cryodetector activities are articulated along dark matter search and
neutrino physics (double and single beta decay for neutrino mass measurement).
Beyond these main objectives, significant development efforts are now focusing
on building matrices of detectors in adjacent fields : BRAIN and DCMB (CMB polarization), XEUS (X-ray astronomy).
Dark matter experiments using cryodetectors are: CRESST (light-phonon),
EDELWEISS (charge-phonon), ROSEBUD (light-phonon), ULTIMA (superfluid
3He), most of these teams assembling their efforts in the EURECA project.
Cryodetectors in double-beta decay are used by CUORICINO/CUORE and for
direct neutrino mass using single beta decay: MIBETA/MARE.
For both dark matter and double beta decay experiments, the main R&D tasks
identified are the following:
•
Increase mass of individual detector (to ≈ 1 kg)
•
Identify surface events (radon progeny) and particularly heavy nuclear recoils
•
Maximize phonon channel sensitivity
•
Identify alternative and most efficient scintillators for signal verification and improved background rejection
•
Develop microcalorimeters with time response in the microsecond range
•
Develop techniques for simpler mass production of superconducting ther
mometers
•
Increase detector reproducibility, decrease cost, and transfer to industry
6.
Dectector elements for Astroparticle Physics
These last two items are fundamental for tonne-scale experiments (EURECA,
CUORE).
In addition, a few major cryogenic and cryoelectronics developments have been
proposed.
•
Load lock system in order to add modules at low (few kelvins) temperatures. This would allow detector exchange or addition without long interruption in data taking
•
Large cryostats without external fluids (liquid N2 and liquid He4).
The generalization of such systems in the next few years is fundamental as the helium cost is expected to increase by a large factor
•
Active compensation of vibrations generated by cryocoolers
•
SQUID electronics : decrease overall cost, multiplexing
•
Ultra-low noise low consumption components (GaAs, QPC, …)
European cryodetector community is involved in several competitive key projects,
with important R&D activities on dark matter and neutrino mass (bb, direct).
The principal groups are: INFN Milano, Como, Genoa, Oxford Department of
Physics, Technische Universitaet Muenchen, Max-Planck-Gesellschaft Muenchen, CNRS IAS/Orsay and CSNSM/Orsay, APC Paris, IPN/Lyon, Néel Institute/
Grenoble, CEA DAPNIA (IRFU). The main industrials are: Supracon, Air Liquide,
Cryoconcepts, Leiden Cryogenics and the nanofabrication facilities : CNR Napoli,
LPN Marcoussis, LETI/Minatech, Minerve Orsay, IPhT Jena. This activity, although
initiated in Europe is more and more dominated by the US groups, benefiting from
an excellent support (NIST, NASA Goddard, Stanford Univ., Berkeley, …)
Recommendations and conclusions
Our most important recommendation to maintain the unity of this high-added
value field divided in small teams is the support (by ApPEC and/or Brussels)
of a European CRYOMATRIX network, already proposed at the first FP7 ITN
(Initial Training Network) but rejected in Stage A. Europe benefits from a
unique team of world-level experts in VLT cryogenics, but its leaders will all
retire within the next 5-10 years (developments often linked to Astroparticle
Physics) : it is fundamental to prepare as soon as possible this difficult transition. The experience accumulated is now used for matrix developments in
other fields (IR and X-ray astronomy, CMB polarization, …) and this effort
should be encouraged.
Contact: G. Chardin, [email protected]
7.
Dectector elements for Astroparticle Physics
1.3.Optical elements, lasers and suspensions for
gravitational wave antennas
Credit: Virgo collaboration
The Virgo beam splitter suspended in the vacuum tower
Ground based laser interferometers such as LIGO, Virgo and GEO are the most
sensitive gravitational wave detectors ever operated. Spectral sensitivities as low
as a few parts in 10-23 have been achieved and some of these detectors are
sensitive to the coalescence of a binary neutron star occurring within 30 Mpc. The
upgrade of these detectors is planned and should be completed by the middle of
the next decade. It will improve their sensitivities by more than one order of magnitude, reaching the point were several events per months could be detected.
In Europe, thanks to the support of the European Commission under FP7, the
design study of a new infrastructure hosting a large laser interferometer devoted
to gravitational wave astronomy is just started. The sensitivity envisaged for such
a detector will allow precise testing of the Einstein theory of gravitation as well as
record the most violent events that occurred in the Universe either recently or in
the remote past.Very likely this new detector, called Einstein Telescope (ET), will
be located underground, operated at cryogenic temperatures and will make use of
quantum optics technology. An intense R&D effort is required to prepare the key
elements of such a detector including high power lasers, larger mirrors and high
quality suspensions elements working at cryogenic temperatures.
8.
Dectector elements for Astroparticle Physics
The main R&D tasks are the following:
Lasers and quantum optics.
The sensitivity of nowadays laser interferometers to gravitational waves with
frequencies larger than a few hundred Hz, is limited by photon shot noise. To
bypass this limitation it is necessary to increase the amount of photons stored
inside the interferometer. One way to achieve this aim is to use more powerful and
stable lasers. Thanks to the rapidly progressing technology of fiber lasers more
powerful laser are becoming available. An R&D program is required to fit this technology to the laser stability requirements of gravitational wave detectors.
As more light will be stored in the interferometer arms the effect of the varying
radiation pressure on the interferometer mirrors will start limiting the interferometer
sensitivity. The combination of photon shot noise and radiation pressure noise is
equivalent to the so called Heisenberg microscope and determines the standard
quantum limit. The use of non classical states of light such as squeezed states
and the development of new optical configurations allows reducing the effect of
the quantum limitation on the ‘gravitational wave observable’.
An R&D program focussed on the development of quantum optics tools for gravitational wave detection should be pursued to overcome this limit.
Keywords: high power lasers, laser stability, quantum optics, squeezed states of
light, interferometer optical configuration and readout.
Larger high quality mirrors.
The interferometer mirrors play a key role in improving the capabilities of gravitational wave detectors. To reduce the quantum limit it is important to build more
massive mirrors, at the same time keeping or improving their optical quality.
Both the optical quality of the mirror substrate and of the coating are important.
Absorption in the coatings determines the amount of power absorbed by the mirror
and thus the importance of thermal lensing. Reducing this absorption allows reducing the constraint on the thermal compensation system and is of crucial importance in the operation of these detectors at low temperatures. The mechanical
quality of the mirror substrate and of the coatings should be improved as well,
since they determine the mirror thermal noise.
To this purpose new materials for substrates and coatings have to be investigated.
Their mechanical and optical properties as a function of temperature need to be
considered. Their thermal conductivity should be as high as possible to allow the
operation of these detectors at low temperatures while the internal dissipation
mechanism should be as small as possible.
The mirror optical quality also determines the amount of light diffused out of the
main optical path. This light may be scattered on non-seismically isolated parts
of the apparatus, like the vacuum chamber, and recombine with the main optical
beam.
9.
Dectector elements for Astroparticle Physics
This effect, already studied for the present infrastructures, will have to be carefully
re-evaluated for future infrastructures devoted to gravitational wave detection.
Keywords: massive mirrors, coating materials, substrate materials, optical quality,
cryogenics optics.
Cryogenics and monolithic suspensions.
Thermal noise limits, or is close to limit, the sensitivity of present detectors. To
improve over the present performance new materials should be considered for
the mirrors as well as for their suspensions. The mechanical quality of the mirror
suspension is one of the parameters to consider.
To this purpose monolithic suspensions made of fused silica have been developed. R&D is on going to improve their reliability. New materials for the mirror
suspension wires should be investigated to be able to operate these detectors at
low temperatures.
Parameters such as thermal conductivity and mechanical losses have to be
studied. Reducing the temperature of operation directly reduces the thermal noise.
In addition, depending on the material, a reduction of the operating temperature
could also improve the mechanical properties of the suspensions allowing a further
reduction of thermal noise.
Keywords: monolithic suspensions, low mechanical losses, material properties at
cryogenics temperatures
Environmental noise and seismic isolation.
Next generation laser interferometers like Advanced Virgo and Advanced LIGO will
start to be limited by environmental noise such as seismic noise directly coupling
to the test masses via varying gravity fields. At that level of sensitivity seismic
noise might also reintroduce noise through residual diffused light recombining with
the interferometer beams.
For this reason particularly quiet sites will be required in the future and underground location might be unavoidable. This assessment will require extensive
seismic characterization. To take full advantage of such a reduction of environmental noise it will be also necessary to reduce the internal noise generated by the
interferometer equipment itself. One of the main needs will be to develop vibration
free cryogenic systems. Such a quieter environment, combined with the development of a new generation of seismic isolation systems will allow pushing the so
called “seismic wall” below 1 Hz.
A combination of different kinds of approaches, including longer and softer seismic
isolators and active isolation systems will have to be considered.
Keywords: underground site and operation, vibration free cryogenics, new passive
and active seismic isolation.
10.
Dectector elements for Astroparticle Physics
Interferometer topology and laser beam geometry.
The interferometer optical configuration determines its frequency response and
the effect of the quantum limitation. Changing the interferometer topology and
combining different interferometers with different orientations allows optimising
the final sky coverage. Different solutions will have to be studied for ET.
Among the technical novelties that might included in future laser interferometers
is the use of high quality gratings to replace the most critical transmitting optics
or the implementation of high order Laguerre-Gauss beams to better spread the
laser power on the optic surface. The evaluation of these solutions has to done by
means of an appropriate R&D program.
Keywords: interferometer topology, high quality gratings, high order laser beams.
Recommendations and conclusions.
The European groups involved in GW detection have contributed to several
of the recent developments that are going to be part of the forthcoming
advanced laser interferometers. Monolithic suspensions, high power stable
crystal lasers, large seismic isolation systems and high quality optical
coatings are well known examples. It is important to support the on-going
R&D activities to help the completion of the Advanced Virgo design. Several
of the European groups involved in GW detection have a long standing tradition in low noise cryogenics systems, thanks to the development and operation of cryogenic resonant detectors.
Thanks to the STREGA joint research activity, pursued within the EU-FP6
ILIAS project, a wide collaboration involving several different groups across
Europe has begun reducing the limitation coming from thermal noise. This
was the first joint R&D involving both the groups working on laser interferometers and those working on resonant cryogenic detectors.
Many of these groups will be involved in the ET design study. This design
study will be the first fully joint project involving all the European countries
working on gravitational wave detection. It will have to be supported with an
intense R&D program to help making some of the decisions required for the
design of ET and to prepare its implementation.
Contact: R. Flaminio, [email protected]
11.
Dectector elements for Astroparticle Physics
1.4.Astroparticle Physics detectors in space
Credit: AMS Collaboration
The Alpha Magnetic Spectrometer
during its intergration at CERN, Geneva
Space is the ultimate laboratory to study the behavior of matter and energy in
extreme conditions and to search for new physics. In this sense space research is
complementary to other Astroparticle Physics fields.
Leading examples of this complementarity are:
•
•
•
•
Indirect search of dark and antimatter matter from space: complementary
to direct search in underground laboratories and to direct production at
high energy accelerators (LHC)
Direct search for nuclear antimatter: complementary to studies of the
properties of antimatter atoms at CERN
Study of extremely energetic cosmic rays : complementary to the ground
based AUGER and, possibly, KM3 and IceCube neutrino detectors
CMB polarisation: early universe cosmology is complementary
to many other areas of particle physics, in particular to GW, grand
unification, supersymmetry, string theories
Astroparticle Physics detectors built for space applications are required to pass
specific qualification requirements to operate in extreme environments (zero
pressure, extreme temperatures, vibrations and shocks, plasma and chemical,
12.
Dectector elements for Astroparticle Physics
ionizing radiation). On the other side the detection technologies employed
by these detectors are in many cases similar to those used in ground based
experiments (e.g. single photon detection, microbolometer), with the additional
requirements of low power, low mass and extremely high reliability.
Leading space missions currently ongoing are:
•
•
•
•
PAMELA: magnetic spectrometer (permanent magnet), in operation
in space since 2+ years: study of cosmic rays composition (up
to 100’s GeV), dark matter (indirect), antimatter
AGILE: imaging calorimeter, in operation in space since 1 year: study
of gamma rays from 100’ KeV to few GeV, high energy Astrophysics
GLAST: imaging calorimeter, launched in may 2008: study of gamma
rays form few 10’s Mev to 100’ GeV, high energy Astrophysics
AMS: magnetic spectrometer (superconducting magnet), on the ISS
starting 2009/10: study of cosmic rays composition (up to TeV’s GeV),
dark matter (indirect), antimatter, gamma rays (>0.5 GeV)
Future missions involving European groups and related R&D are:
1) Extreme Energy Cosmic Radiation (EECR) detection from space: JEM- EUSO
(Japan-ISS), super-EUSO (R&D in the framework of Cosmic Vision). The goal
is to measurement of CR around and above the GZK cutoff as follow up of
Auger (S/N) experiments. The technologies needed requires a vigorous R&D on:
•
•
•
•
Photon detectors : SiPM and associated electronics (links to R&D for
higher
efficiency
Cherenkov
Telescope
focal
planes)
Large optics : large foldable optics (links to new generation of space teles-
copes or to Earth observation telescopes), formation flight multiple optics.
Ultra low power electronics and on board processing for
large number of readout channels(>106)
Precursor microsatellite mission, to accurately measure the time structure
and geographical location of the background UV sources
2) Ultra high precision measurement of low to medium energy cosmic
rays to search for dark matter induced effects (follow up of AMS).
These experiments would be done by developing the technique of Long Duration
Balloons (LDB) from the North Pole (Svalbard Islands). Experiments being studied are
•
PEBS: measurement of e+/e- , from a few to a few hundreds GeV
•
DbarSUSY: measurement of low energy antiDeuteron, from 0.1 to a few GeV
13.
Dectector elements for Astroparticle Physics
The technologies needed require a R&D on
•
•
•
•
Telemetry : setting up a network of telemetry system for long duration
balloon flights (30-40 days) from the Svalbard islands (European
Industries)
Permanent and superconductive (SC) magnet : development of permanend or SC magnets to be deployed on ballon spectrometers
(strong european expertise, in Germany, Italy and UK)
Fiber tracking readout with SiPM
Large area RICH, eg. DIRC readout with SiPM
Similar technologies are required for the development of a detector to
measure CR composition at the knee from a Russian mission (NUCLEON):
•
•
light calorimetric techniques (particle counting)
large, light TRD systems for particle ID
3) BPOL : next generation ESA cryogenic CMB experiment devoted to the
measurement of CMB polarization (Cosmic Vision). Study of the very early
universe development and structure, unification of forces, gravitational waves.
The technologies needed requires a vigorous R&D on cryogenic arrays of
CMB bolometers (MKID). On this area there is a common interest of ESA. In
addition the technology being developed for the arrays of CMB detectors is of
interest also for new generation double beta decays experiments (see above).
Recommendations and conclusions
The European space community involved in Astroparticle Physics has a
world wide lead on several competitive projects with important R&D activities on dark matter, antimatter, EECR, high energy Astrophysics, Cosmology.
European lead should be maintained supporting this area with the help of the
various space agencies but also developing facilities (eg. Ballooning around
the North Pole from a base on the Svalbard Islands) allowing for continuing R&D
and experimental activities while preparing for the next large space mission.
Important cross links exist with other fields, both from the science point of
view (dark matter, supersymmetry, grand unification, CP violation, B violation…) as well as from the technology point of view (low temperature, low noise
electronics, compact photon counters). The high quality standard of space
detectors is a specific technology which is very important also to improve
the reliability for ground based detectors operating in extreme environment.
Contact: R. Battiston, [email protected]
14.
Dectector elements for Astroparticle Physics
1.5.Distributed Electronic and Acquisition
systems for Astroparticle Physics
The large detector arrays deployed in the desert or the bottom of the sea as well
as the future large ground and underground facilities based on water, LAr, liquid
scintillator tank have common features such as the distribution of sensors around
a large volume, the absence of external triggers, the large amount of data to be
reduced and partially processed locally, the need to rely on standard technology
that can be easily upgraded after years.
All these requirements are fulfilled in the so-called Ethernet capable «smart
sensor». DAQ architectures for which each sensor (e.g. a photodetector) in the
experiment is seen as a node with embedded processing power in a standard
Ethernet network. The OPERA experiment made the demonstration that such an
original technology was effective in the framework of a large experiment. These
systems have the advantage of a low cost, a high reliability, small dead time, infinite modularity and constant upgrades of the performances. The improvements
under study in this field are the following :
•
•
•
•
•
•
Increase the bandwidth
Reduce the local CPU loss by treating the network layer at the hardware
level
Reduce the number of protocols for data transfer and synchronization matters
Go from custom boards to a more stable standard developed for
telecommunications applications
Keeping a generic processor board and a specific FE interface
Power issues when the sensors are developed in an autonomous
mode (e.g. AUGER)
Recommendations and conclusions
All improvements are currently under evaluation, developments or tests
in different labs. A common effort should be made to get less
isolated teams and to setup common design framework.
Contact: J. Marteau, [email protected]
15.
Dectector elements for Astroparticle Physics
1.6. Fast and low-cost front-end read-out systems
for Astroparticle Physics
The number of electronics channels associated with Astroparticle Physics detectors is constantly increasing to cope with the advances in the detection techniques, while the technical requirements remain stringent concerning the bandwidth
and the speed of the acquisition. The readout chain must be designed to have a
wide bandwidth of 500-700 MHz, which together with a high sampling frequency on the order of a GHz - allow to fully exploit the time characteristics of Cherenkov
showers (few ns duration) while reducing the background from the background
noise (from the night-sky for atmospheric Cherenkov telescopes, or from undersea
light-sources in cosmic neutrino detectors).
The cost and power consumption of standard solutions (such as flash ADCs) are
a barrier to further development. One solution to this problem which is in use and
being pushed even further in current developments is the use of ASICs (application-specific integrated circuits) which are capable of integrating the fine timesampling (using analogue memory pipelines) and the ADC functions in a single
chip. Integration of further elements on these ASICs is the clear future step to be
followed.
For instance, the ARS (Analogue Ring Sampler) was developed at SEDI-Saclay
for the ANTARES neutrino experiment [1], and is currently operating in the hostile
deep-sea environment off the coast of Toulon, French Mediterranean.
In Cherenkov Astronomy, the number of channels has increased from ~100 in
1990 (Whipple observatory) to ~500-1000 in the mid to late 90’s (CAT, HEGRA),
to a several thousand in the current most sensitive instruments (H.E.S.S., MAGIC,
VERITAS).
The latter two experiments currently use flash-ADC technology. H.E.S.S. has
pioneered the use of the ASIC analogue memory technology in Cherenkov Astronomy. This development consisted of the adaptation of the ARS0 chip - developed
initially for the ANTARES - for use in H.E.S.S. phase 1, allowing the construction
of a low-cost, fully-integrated fast-electronics camera for each of the four H.E.S.S.
telescopes.
The MAGIC experiment is exploiting similar developments in analogue pipeline
technology, with the DOMINO ring sampler chip developed for the MEG experiment at the Paul Scherrer Institute (PSI) [2], which will be applied to upgrades of
the MAGIC camera and to the MAGIC-II telescope.
16.
Dectector elements for Astroparticle Physics
H.E.S.S. has advanced with the development, with the SEDI-Saclay, of a specific
dual-channel ASIC, named SAM (Swift Analogue Memory) [3], to meet the more
stringent requirements for the new H.E.S.S.-II telescope. The SAM, which uses the
3.3V CMOS AMS 0.35µm technology, is configured as a matrix of 16x16 capacitors which enables a readout speed > 4x105 events/sec. The dynamic range and
input bandwidth are increased up to 12 bits and 300 MHz respectively while the
cross-talk is less than 3 per mil. The chip functionalities are fully programmable
through a serial link. The sampling rate is controlled by an external clock and can
be changed from 500 MHz up to 2.5-3 GHz, with power consumption of the order
of 300 mW. By the end of 2006, prototype chips have been successfully tested and
a series of 4000 units have been produced and tested.
The next step consists in the development of a fully integrated solution including
amplifiers, data buffering and digital conversion inside a unique ASIC with also the
elaboration of the first level trigger information. Such a development is primordial
for the future CTA (Cherenkov Telescope Array) project, which consists of several
tens of telescopes with a total of the order of 10 5 channels. A low-cost, low-power
solution to the signal-acquisition is evidently required, and the ASIC functionality
should also greatly improve the reliability of the solution, which is crucial for such
an extensive project.
Recommendations and conclusions
Pursue the development of ASIC analogue memory technology, including
the difficult problem of integration of the digital elements (ADCs, FIFO buffering) and the fast analogue elements (memories, comparators for trigger) on
the same ASIC. For this and many domains in both Astroparticle Physics
and Particle & Nuclear Physics, the know-how of the teams involved (SEDI,
PSI, and associated laboratories involved in the cutting-edge experiments in
the field) should be supported, fostered, and kept up-to-date with the latest
developments in ASIC technology.
Contact: Pascal Vincent, [email protected]
[1] Lachartre D. and Feinstein F., NIM-A 442 (2000) 99-104
[2] S. Ritt, NIM-A518 (2004) 470.
[3] E. Delagnes et al., NIM-A 567 (2006) 21-26
17.
II
MATERIALS FOR
ASTROPARTICLE PHYSICS
Materials for Astroparticle Physics
2.1.Noble liquids for dark matter and double beta
decay
Credit: INFN - Richard Walker, Imperial College London Example of a liquid noble gas detector: the photomultiplier array
and field grids for the ZEPLIN-III two phase xenon detector.
The main Astroparticle Physics focus for liquid/gas noble gas detectors is currently in
the fields of direct dark matter searches and neutrinoless double beta decay. In addition,
large scale liquid noble gas detectors are under study as targets for superbeam systems
and proton decay studies. The ability to use liquid noble gases as dense, high sensitivity
gamma counters with good position reconstruction and low threshold also lends these
types of targets to medical imaging, with several R&D studies already completed in this
area.
•
•
•
•
Direct dark matter searches: Xenon (ZEPLIN, XENON), Argon (ArDM, WARP)
Neutrinoless double beta decay: EXO
Proton decay and large volume beam targets: LAGUNA / T2K_LAr, …
Medical imaging
The wide range of applications for liquid noble gas targets means that R&D has been
undertaken in many aspects of the application and underlying physics of noble gas
systems. The focus on dark matter detectors has been to understand and improve
the low energy response and backgrounds for liquid xenon and argon, for neutrinoless
double beta decay studies the focus has been on energy resolution and parent-daughter
19.
Materials for Astroparticle Physics
identification in liquid xenon, for the large scale system the R&D has focussed on management and containment of (usually) liquid argon and the ability to maintain good track
identification and maintain the high charge/light yield.
For dark matter detectors areas of interest for R&D are:
•
•
•
•
•
Assessment of discrimination through high field operation
Reduction of backgrounds of readout systems (PMTs, etc)
Improvement of efficiency of photon and charge readout systems
Reduction of backgrounds of target materials, including the gases themselves
Improvement in the understanding of low energy physical processes
and detector performance (relative scintillation yields, improved discrimination
<10keVee)
Areas of possible improvement through R&D for charge and photon readout,
which are dependent on the wavelength of scintillation light (175nm for xenon,
125nm for argon):
•
•
•
•
•
Development of large area, low temperature operation, low background PMTs
or their replacements
Use of APDs, HPD or Si-PMT devices in noble gas detectors
Use of photocathodes within target volumes
Use of GEMs, LEMs, micromegas, strip readouts
Development of stable wavelength shifting options
In addition to R&D underway in most dark matter collaborations to reduce the residual backgrounds in detector systems after shielding, such as development of low
background PMTs (as above) R&D is required to reduce the intrinsic background of the
noble gas itself.
•
•
•
•
Noble gases are highly purify-able through distillation, ion exchange, hot
getters, sublimation pumps, etc. and can be re-purified and distilled as
appropriate and as required. The electronegative gas contaminants can thus
be removed efficiently.
Can re-purify and distil as appropriate
Residual activity may arise from isotopes or isobars, especially 39Ar in argon
(at ~Bq/kg levels) and 85Kr in xenon (from the atmospheric production)
R&D is underway in removal or exclusion of these intrinsic backgrounds,
through sourcing of argon from underground locations, use of pre-bomb
test xenon, multiple distillations and chromatic separation.
20.
Materials for Astroparticle Physics
For neutrinoless double beta decay, current areas of R&D being pursued in
liquid xenon include, in addition to aspects already incorporated above, such as
maximal light and charge readout, are:
•
•
•
Ba-ion trapping and extraction to identify daughter nuclei using cold tip extraction
Laser tagging and observation to identify event location
Enrichment and extraction of 136Xe as a neutrinoless double beta decay source.
The enrichment of xenon also has implications for dark matter searches where
axial-scalar couplings may be investigated though odd-even separation of
xenon isotopes
Large scale, multi-tonne liquid argon detector systems for superbeams have ongoing
R&D into the following area:
•
•
•
•
Containment of multi-tonne liquid noble gases
Gas management and safety mechanisms
Generation and maintenance of magnetic fields
Extreme purification of argon target
Recommendations and conclusions
European groups involved in liquid noble gas and liquid/gas noble detector
systems have a long and proven track record in the development of detectors for
specific, targeted, areas of physics and astrophysics. To capitalise on the experience and expertise of these groups it is recommended that R&D funds be developed through ApPEC/ASPERA processes to facilitate additional development of
this technique for those fields already under study, and to further knowledge
exchange into other areas of science and technology, especially that of medical
imaging. Common areas with other R&D fields include photon/charge readout,
DAQ systems, low energy recoil facilities, low background material development.
Contact: Nigel Smith, [email protected]
21.
Materials for Astroparticle Physics
2.2.Scintillators for neutrino physics and proton
decay
Credit: INFN - Borexino detector
Liquid-scintillator detectors feature a high energy resolution and a low energy detection
threshold combined with efficient means of background reduction. As scintillators can
be based on relatively cheap organic solvents, large volumes are affordable and can be
used for experiments for events like neutrino detection or rare decays.
Up to the recent past, experiments based on this detection technique have made valuable
contributions to the field of Astroparticle Physics and especially neutrino physics. Both
the CHOOZ and the KamLAND reactor neutrino experiments significantly contribute to
the limits and precision measurements on neutrino oscillation parameters.
Especially the KamLAND experiment was essential for the proof of neutrino oscillations.
In 2005, the collaboration reported the first detection of terrestrial neutrinos. Originating
from the radioactive decays of Uranium and Thorium in the Earth’s crust and mantle,
these neutrinos offer a unique opportunity to explore the interior structure of our planet.
Like nuclear reactors, the Sun is an important source of neutrinos. As an enormous
effort was made to free both the scintillator target and the surrounding installations of
radioactive impurities, the Borexino experiment measured for the first time the solar Be7
neutrino flux directly and is now leading in the detection of low-energetic solar neutrinos.
Borexino is anticipated to disentangle the contributions of various fusion processes being
part of the Sun’s energy production. Finally, all these large scale scintillation detectors
22.
Materials for Astroparticle Physics
are sensitive to neutrinos from core-collapse supernova explosions, which will provide
real-time information on the formation of neutron stars and black holes.
European groups play a leading role in large volume, low radioactivity scintillation detectors. A large number of physics institutes all over Europe is involved in the maintenance
and analysis of running experiments and the further development of liquid scintillators.
•
INFN groups in LNGS, Milano, and Genova (Italy)
•
University of Cracow (Poland)
•
Kurchatov Institute Moscow, Dubna University (Russia)
•
C. E. A. Saclay, Paris (France)
•
Technical University of Munich, MPI-K Heidelberg (Germany),
In addition, companies producing the organic solvents necessary for scintillator production, as the Petresa Group, have shown interest in promoting further R&D activities in
this field.
As the full potential of this detection technique is not tapped yet, a number of
possibilities is investigated:
•
•
•
The search for optically even more transparent solvents and for efficient
solvent-purification methods is in progress and already has returned promising results. Purification also includes ways of further increasing the radiopurity of
the scintillator to reduce the internal background of the detector.
The wavelength-shifters (fluors) dissolved in the scintillator are influencing both time resolution and light transport. There is an on-going search for fast fluors
with short fluorescence decay times or with large Stoke’s shifts that would
reduce the optical self-absorption of the scintillator.
As the detection medium is liquid, there is the possibility to solute small
amounts of foreign atoms or molecules in the scintillator. These loaded
scintillators could for instant be used for a more efficient detection of antineutrinos (by adding Gadolinium) or solar neutrinos (by adding Indium).
Moreover, adding an adequate candidate like Neodymium will allow the
search for neutrino-less double-beta decay. However, stability and optical
transparency of the end product are essential for this approach.
23.
Materials for Astroparticle Physics
Based on the on-going developments, a number of detectors have been proposed
by both European and non-European groups that represent the next generation
of low-energy neutrino experiments:
•
Several upcoming reactor experiments like the European DoubleCHOOZ
project as well as Daya Bay, Angra and RENO are hunting for the last
unknown neutrino mixing angle q13. Apart from the further exploration of
neutrino oscillations, these projects pave the way for the surveillance of n u c l e a r
power plants by monitoring their neutrino emission. In this way, future neutrino detectors might be able to add to the global effort on non-proliferation of nuclear
material.
•
Using the infrastructure of the successfully completed Canadian SNO
experiment, new measurements with a target of Neodymium-loaded scintillator
is proposed. Compared to other approaches, the new SNO++ detector would
balance its lower energy resolution with a vast amount of decaying nuclei,being
competitive with leading-edge double-beta experiments. Furthermore, liquid-scintillator calorimeters are under discussion for the deployment in the SuperNEMO
double-beta experiment, proofing the versatility of this detection technique.
•
A liquid-scintillator detector with a target of a mass of the several tens
of kilotons will allow the investigation of presently known neutrino sources at
unprecedented accuracies. Detectors like the European LENA project or the
US-proposed Hanohano will search for underlying and non-standard effects
in the time and energy spectra of terrestrial, solar and supernova neutrinos.
Moreover, the combination of large target volume and efficient background
discrimination will provide the sensitivity for the detection of the diffuse
supernova neutrino background and for pushing the present limits on proton
lifetime for the SUSY-favoured decay into a Kaon and antineutrino by an order of
magnitude.
Recommendation and conclusions
Liquid-scintillator detectors have proven their merits when they played a central
role in the discovery of neutrino oscillations. European liquid-scintillator experiments are playing a leading role in this detection technique. First steps towards
the next generation of large volume detectors have been made by the funding of
the European LAGUNA design study. In this frame, the investigation of possible
underground sites for large-volume detectors is promoted. Further research
concerning the technique based on scintillators is complementary to this program
and is necessary to obtain a consistent picture of the design and the full scientific potential of such detectors. The construction of these next generation large
volume detectors is expected to start from 2010 on, for which adequate funding
should be allocated.
Contact: M. Wurm, [email protected]
24.
Materials for Astroparticle Physics
2.3.Analysis on rare isotope preparation for
Astroparticle Physics
Rare Isotope production will play a crucial role in the future experiments in Astroparticle Physics. In particular large amount of isotopically enriched materials will be necessary for future experiments on double beta decay (DBD) and dark matter Search (DM).
Complete preparation of the bank of enriched isotope in DBD experiments was an
important results obtained during the ILIAS activity in the FP6 framework of the European Community.
Information collected for the preparation of this “table” indicate clearly that for future
experiments the amount of isotope masses involved will be on a complete different
scale: actual experimental masses are in the range of few tens of kilograms but for the
next generation experiments we are moving in the direction of tons mass scale.
There is also another important issue that must be taken into account: the purity of the
material needed for such future experiments will be extremely high.
Just to compare, actual experiments on DBD show background in the range of
0.1 counts/(keV kg y) but for future the target is to reduce this value by at least one or
two order of magnitude. Looking forward, isotope enriched productions must be very
clean and any effort will be spent in the direction of the purification of the produced
materials.
Summarizing these aspects, for the future experiments we need large isotopically enriched masses showing a very high purity. These requests drove us in the studies of all
possible approaches to isotope enrichments in a structure where all possible DBD and
DM experiments must be considered.
These aspects will be of extreme importance because the production and purification
productions of these isotopes will need a considerably large budget that must take into
account not only experiments now under construction but also a second generation
experiments that can be ready in 15/20 years.
To define possible strategies we had, in a first step, tried to identify the possible production sources for the enriched isotope. Actual production capability is mainly driven by
the Russian plants where installation of large number of ultracentrifuge will create, apart
potential purity problems, the right conditions for massive isotope productions for many
different elements that can be prepared in a gas form.
At the same time the current prices of isotopes from Russia are favorable and some
effort was spent to push the Russian researchers to collaborate in the future experiments. Some worries come from the fast growing of the Russian economy and for the
difficulties in controlling the complete isotope production that can create problems in the
future real cost estimations of the Russian suppliers. In west countries there are actually
no real installation for isotopes production, apart that dedicated to the nuclear power
plants: only Urenco factories could be an exception.
25.
Materials for Astroparticle Physics
USA calutron was stopped in 2004 and probably do not restart any more, medium size
Isotope Cyclotron Resonance (ICR) machine was installed in USA factory Theragenics
but is used only for medical applications.
Apparently ultracentrifuge machine in Japan will be difficulty used for application in
Astroparticle Physics experiments. Instead there is a real chance for Nd150 production,
very interesting and very important isotope for DBD study, which was opened at the
end of 2007 after the decision of CEA in France to consider the possible restarting of
an AVLIS machine: this means that if the restart succeeds, a large amount of Nd150
isotope will be produced, but only this isotope.
Within this scenario, we believe that there is the necessity to clarify a real approach
to the enrichment program for the next 10 years, at least. We tried to identify some
possible strategy that can be summarized in 4 possible ways:
1)
2)
3)
4)
Arrange for an agreements with the Russian producers
Explore the interests and capability of Urenco company
Restart some dedicated plants in west countries
Build a complete new dedicated facility in Europe
The first approach is the most direct and, probably, the simplest one.
The reasons are: Russian enrichment plants exist, actual price per unit product is convenient, Russian ultracentrifuges are technically fairly good and people have lot of experience in isotope enrichments.
Obviously there are also some drawbacks: only isotopes that have some gas compounds
can be enriched, produced material must be normally cleaned after the enrichments,
there are no ideas regarding the future price dynamics and also without a direct involvements of Russian researchers it is difficult to imagine an R&D program.
On their side, Russian should acquaint us about status and production capability of their
calutrons.
As far the third solution, the restarting of the AVLIS machine in France, if confirmed,
must be considered a very important success. First of all because this machine can
produce large amount of one isotope, Nd150, that cannot be enriched using ultracentrifuge, second because it indicate a possible way also for other enrichments centers.
However this plant has a special peculiarity: since it is an exploitation of a large existing
plant built for other isotopes, it can produce large amount of material in a very short time
but at the end it cannot be reconverted for other isotopes. That means initial considerable
economical investments just for an isotope preparation. For other possible installation
AVLIS-like this approach is not usual: normally we will aspect relatively low throughputs
that cannot satisfy the DBD experiment requests for remaining inside defined time schedules.
Moreover laser based technique are limited to a handful of isotopes.
26.
Materials for Astroparticle Physics
The last possible solution deserve considerations for many points of view: a plant specifically dedicated for DBD and DM isotope production can be realized, production capabilities can be hopefully matched with the purity request and also economical aspects
can be considered in order to remain competitive on the market.
Finally dedicated R&D for specific isotopes can be realized. It is clear that a project that
plan to build a complete enrichment facility must obtain the support and the agreement
of large number of experiments, it needs a relatively initial large investment for its realization and also it is necessary to spend time to identify the correct construction site and
the realization of the plant.
During the last two year we had tried to find an agreement in order to propose to the
scientific community the realization of a new isotope enrichment plant based on an ICR
machine: this choice is strictly related to the versatility of this machine that will allow, in
principle, the production of all the needed isotopes for future experiments.
This agreement is necessary to prepare a possible design study to submit to the FP7
program of the European Community. At the moment the agreement was not found and
as the time passes probably this solution will become unrealizable.
Recommendation and conclusions
Considering all the reported ideas and analysis what we can conclude is that for
future Astroparticle Physics experiments we need a real effort in order to organize all the requested enriched isotope productions, the strategy must be fixed
soon or we risk to have a big increase in prices of materials and a long delay
in the realization of the experiments. Actually and for the near future the best
approach seems to be the direct contact with the Russian labs with their direct
involvements in the definition of a realistic strategy for the future. Using this
direct contact it is probably possible to freeze the price increase and also it can
be possible some R&D steps specifically dedicated for the production of enriched isotopes for DBD and DM experiments. The realization of a dedicated facility
remain an interesting option that can be pursued if a substantial consensus will
be find in the community, also looking to the possibility to enrich isotopes that
normally cannot be prepared using ultracentrifuge machines.
Contact: Ezio Previtali, [email protected]
27.
III
NEW TECHNIQUES FOR
ASTROPARTICLE PHYSICS
New techniques for Astroparticle Physics
3.1.Radiodetection
Credit: A.M. van den Berg
Detectors at the Pierre Auger Observatory in Argentina used for the detection
of air showers.
The origin of ultra-high energy cosmic rays poses one of the largest challenges in
modern physics. Presently, Astroparticle Physics is entering a new era using large-scale
detectors on the surface of the Earth, embedded in the icecap of Antarctica, and using
the deep-sea in the Mediterranean.
Classical techniques for the detection of cosmic rays include extensive-air-shower
observations at ground level using for instance a large array of charged-particle detectors which covers hundreds to thousands of square kilometres.
Alternative optical techniques include observations of Cherenkov light in air, water,
and ice, as well as observations of fluorescence light from nitrogen molecules in the
atmosphere. These techniques are well advanced but become expensive for the instrumentation of the next generation experiments. They are limited to close-by in situ instrumentation of sensors in media as water and ice. Or in the case of the observation of
Cherenkov and fluorescence light in the atmosphere one is limited to clear and moonless nights, leading to a duty cycle of only 10%.
Therefore, if observatories will be expanded, new detection techniques have to be developed and tested.
Within a European R&D program we aim to develop new and cheaper detection techniques with a large potential for application in the next generation of big experiments.
29.
New techniques for Astroparticle Physics
The technique considered here is the detection of radio signals emitted by chargedparticle showers induced by high-energy cosmic rays and neutrinos. The general advantages of the radio technique lie in the fact that radio waves are easy and cheap to detect
and that they propagate in a number of media without much attenuation. Therefore,
radio signals can, in principle, be transported over large distances in the atmosphere
(many 10’s of kilometres) or through dielectric solids as ice and rock salt through many
hundreds of meters.
Presently, there are small-scale radio detection arrays operational where cosmic ray
events are being observed as they enter the Earths atmosphere. As these arrays are
located at existing cosmic ray air-shower observatories, detailed studies of radio signals
can be performed as a function of the measured shower parameters (energy, arrival
direction). More rigorous R&D efforts are needed to enlarge the scale of such arrays to
an area of more than 1000 km2. For the observation of the highest energy neutrinos vast
detector volumes might be required, as large as 10 km3 or even more. The instrumentation of such volumes with conventional detectors (optical sensors) seems to become
extremely expensive.
Therefore, other detector materials and techniques, e.g. based on acoustic and radio,
will be needed and dedicated R&D projects focused on these new techniques are
thus a necessity. As with radio detection of cosmic events in the atmosphere, a hybrid
detector based on different detection technologies seems essential to benchmark the
data obtained with these new techniques based on radio and acoustic signals against
existing techniques based on the detection of neutrino-induced Cherenkov light in ice
or water. At the South Pole we foresee the deployment of all three techniques at the
IceCube site, requiring extensive detector simulations.
As the attenuation length of radio and acoustic signals in dielectric bulk materials as ice
and rock salt are hardly known, in-situ measurements will be needed as an essential
step towards such a huge neutrino detector. An even larger detection dielectric volume
is available if one uses the surface layer of the moon. Existing ground-based radio
observatories in Europe, mainly designed for astronomical surveys (e.g. WSRT and
LOFAR in the Netherlands) are capable to monitor the surface layer of the moon with
high spatial resolution over a wide frequency domain. In addition, moon orbiting satellites are being developed for the same purpose. These systems have huge detection
sensitivity per time unit for the observation of extremely high energy events hitting the
moon.
Analysis and data-reduction techniques
These types of observations will be performed using distributed sensor networks, where
individual radio detection stations are connected. At various levels in this network, data
processing occurs at the local stations, within the connecting network, and in the central
station. In all cases, the signals observed in the radio bands are very weak and thus
vulnerable for unwanted interferences.
30.
New techniques for Astroparticle Physics
As the interesting events are very rare compared to these interferences and because
networks are bandwidth limited, an adequate event filtering and triggering system has to
be used at an early stage in the signal processing chain (i.e. at the sensor station).
There are several techniques both in the time and in the frequency domains, which
can be used. However, their implementation in the data-acquisition chains has to be
studied in detail to optimize to true-to-false trigger ratio and to avoid an overload of the
available network bandwidth. To optimize the available bandwidth for data transport,
network-embedded algorithms have to be developed. These algorithms use the space
and time information of selected data obtained at the various sensor stations. Using
pattern recognition methods noise reduction can be achieved at an early stage and an
optimal data rate of good events through the network can be achieved at minimum costs
for the bandwidth capacity.
Advances in low-power digital electronics, fast high-dynamic analogue-to-digital converters (ADCs), internet, and wireless networking technology make the technical feasibility
of these noise-reduction methods very promising. These techniques, though at quite
different sampling frequencies, are also used in acoustic detection.
Hardware developments
Most of the radio-detection systems are located in remote areas requiring self-sustained
power systems and wireless communications. Voltaic systems based on solar or wind
power and batteries are a cost-driving part of the station hardware. The development
and possible integration of wireless communications with the station electronics aiming
at low-power consumption while maintaining a high data rate (> 1 Mbps) over long
distances (> 500 m) with a high uptime is therefore a necessity for the deployment of
the radio sensors over large area (> 100 km2).
This type of hardware will be deployed in rather hostile environments and should last
for many years. Outside the field of Astroparticle Physics, the application of this type
of hardware together with its embedded trigger and analysis techniques is foreseen for
large-scale remote sensing of environmental or seismic parameters.
System health and calibration methods
A crucial ingredient for the long-term operation of solitary sensors in remote areas is the
monitoring of the performance of each and individual sensor. The monitoring is required
with regard to noise levels and its long-term fluctuations, stability of the signal gain
and timing properties. Because of the large number of sensor stations foreseen and
their remote location, the development of automatic feedback and correction systems
is essential.
Site specific studies
As cosmic neutrinos have not yet been discovered (apart those originating from the Sun
and from SN1987A), future detector systems might be required with a volume much
larger than 1 km3. The Earths atmosphere and dielectric materials as ice and the lunar
regolith can be used as detectors in which radio signals are produced, either through
31.
New techniques for Astroparticle Physics
synchrotron radiation or through Cherenkov radiation. If one uses the atmosphere as a
target and if one detects horizontal air showers one may have a clear signal for Earthskimming cosmic neutrinos. For this purpose, selected sites have to be studied carefully
with respect to interferences which are transported over long distances through the
atmosphere (e.g. remote thunderstorms). As an alternative for ice and water, rock salt
can be used as a target material for the detection of high-energy neutrinos. Rock salt
has the advantage of a relatively high density compared to water and the availability of
substantial salt layers at various places in Europe, e.g. in Germany, Poland, Romania,
and The Netherlands. Radio detection arrays in solids can be co-located with acoustic
detector systems. For both detection techniques signal attenuation lengths, noise levels,
and issues concerning logistics and deployment have to be studied.
Recommendation and conclusions
Presently, Europe is playing a leading role in the development and use of
radio detection techniques for high-energy cosmic rays and neutrinos.
Therefore, an active and timely R&D effort should be maintained on a European scale to further improve and develop the radio-detection technique.
This will enable researchers to use these new type of detetors for very
large detector areas and volumes, specifically designed for ultra-high energy
cosmic and neutrino Astrophysics.
The development of these techniques on a large scale opens opportunities for
industrial applications.
Credit: A.M. van den Berg
Prototype of a radio-detection system at the
Pierre Auger Observatory in Argentina used for
the detection of air showers
Contact: A.M. van den Berg, [email protected]
32.
New techniques for Astroparticle Physics
3.2.Acoustic detection of Ultra High Energy (UHE)
neutrinos
Recent years have seen dramatic advances in the number and quality of observations
of various astrophysical objects using probes of the Universe such as gamma rays and
cosmic rays.
The detection of neutrinos from these high energy sources will provide important complementary information on the underlying astrophysical processes, e.g. neutrinos indicate
the acceleration of hadronic material in the source, a distinction that high energy gamma
rays cannot make.
At present, large volume high-energy neutrino detectors are operating in both the Mediterranean and at the South Pole, these devices employ large area photosensor arrays
to detect optical Cherenkov light produced by high energy neutrinos.
Due to the relative scarcity of high energy neutrinos however larger volume detectors
are required.
Cubic kilometre scale devices are currently either under construction (ICECUBE at the
South Pole) or in the design stage (KM3NeT in the Mediterranean).
A complementary method of detecting UHE neutrinos via their acoustic signature left
in either water or ice also exists and European groups are amongst the forerunners
developing this novel technique. At present a number of EU-led initiatives (ACORNE,
AMADEUS, ONDE, SPATS) have been or are being operated at various deep sea/deep
ice sites, some in conjunction with existing optical Cherenkov detectors.
The following defines a programme of work that will ultimately result in a mature
acoustic detection technology that could be integrated into optical Cherenkov detectors.
In the case of detectors at the South Pole then Radio Cherenkov detection, discussed
in Section 3.1, should also be considered in this exercise. This approach of hybrid
large area/large volume Astroparticle Physics detectors has already been successfully
demonstrated in cosmic rays detection, e.g. the simultaneous use of Nitrogen fluorescence and Cherenkov light in the AUGER detector.
Furthermore, European science stands to benefit if complementary technologies such
as the optical and acoustic neutrino detection techniques are co-deployed since economies due to the sharing of deployment costs and use of the same mechanical, digital
and power infrastructures will be possible.
Software development:
The EU groups have developed some excellent software to perform tasks such as
programs to simulate the energy deposits from UHE neutrinos and integrators to correctly
calculate the expected acoustic signal from an incoming neutrino. Areas where further
development is foreseen include reconstruction, analysis algorithms and simulating
hybrid detectors. Reconstructing the characteristic planar neutrino-induced acoustic
signal is desirable since it gives a measure of the incoming direction of the UHE neutrino
33.
New techniques for Astroparticle Physics
which is perpendicular to this plane. However, temperature gradients in detection media
such as ice and water cause refraction which results in a hyperbolic acoustic signal
path on a distance scale of a few kilometres. Careful study of reconstruction techniques to include the refraction effects is required if a reasonable pointing accuracy of an
acoustic array is to be achieved. The differentiation between the characteristic bipolar
neutrino signal events and acoustic background events from various sources is also
necessary. It is foreseen to develop fast data reduction and data analysis algorithms
to reject different background event classes. Finally, it will be necessary to develop the
means, in software, of rapidly assessing the sensitivity and performance of different
acoustic detector configurations as part of a potential future hybrid detector.
Sensor development:
At present, the acoustic sensors of all existing acoustic arrays being used for the
investigation of acoustic particle detection techniques are hydrophones based on the
piezoelectric effect. Whilst good quality “off the shelf” commercial hydrophones and
glaciophones do exist it is advantageous to develop bespoke acoustic sensors whose
characteristics such as frequency response (band width, resonances, phase delays)
and the directionality are well-matched to the detection of UHE neutrinos. Several selfmade hydrophones are currently in operation in the AMADEUS setup (Erlangen). Alternative techniques are also being explored, e.g., hydrophones based on a DBR fibre
laser on an erbium-doped 1550nm optical fibre, photo-imprinting with Bragg gratings
(Pisa). These sensors have sensitivities comparable or better than commercial piezo
hydrophones and can be used up to static pressures of 350 atm. Similarly, a different
kind of acoustic sensor based on a coil of optical fibres wound on a mandrel that can
be used as a microphone or a hydrophone has been proposed (Genova). The fibre coil
has a reflector at each extremity to produce the sensor arm of a Michelson interferometer: the pressure wave is therefore sensed using the coil as the active arm of the
interferometer. These «optical» hydrophones demonstrate some important advantages
compared to the piezoelectric ones, e.g. they are completely passive and are free from
electronic noise.
The following R&D activities are foreseen: investigate alternative technologies, in particular «optical hydrophones»; development of improved glaciophones; with the experience gained from the existing acoustic arrays, optimize the design of custom-made
piezo-based hydrophones (here both experimental tests and computer simulations
are required); investigate and develop designs to be used as “add-on” in future optical
Cherenkov detectors such as KM3NeT, for example, multi-purpose hydrophones for
use in acoustic positioning and as neutrino detection sensors and/or a design that is
easily combined with photomultipliers.
Calibration methods and techniques:
The use of well-calibrated sensors will play an important role in the development of
acoustic sensors. A principal requirement is for a calibration system comprising acoustic
transmitters which will be used not only to produce tests signals for the acoustic sensors
34.
New techniques for Astroparticle Physics
but as test “neutrino” sources. In order to generate specific waveforms the transmitting
hydrophones have to be well-calibrated with the form of the transmitter signal being as
close as possible to that expected from a high-energy particle. Piezo elements, hydrophones, pulsed lasers or wires heated by short current pulses can all be considered for
this application. However, any calibrator must be prepared for the installation in water or
ice, and their properties (frequency and temporal structure of the acoustic signal, stability, dependence on environmental parameters, etc.) have to be understood in detail.
The most convenient way to generate and control this kind of signal is directly from
acoustic transducers, but some R&D is still needed to achieve a transmitter which fulfills
all the properties of the signal with respect to the temporal and directional parameters.
Several studies involving different techniques (equalization, parametric sources, arrays
of transducers) are under way to develop transmitters that can mimic a UHE neutrino
signal, whilst bearing in mind practical issues such as ease of deployment and operation.
Furthermore, the development of protocols for testing and calibrating acoustic sensors
for a deep-sea array, both in the lab and in-situ at the deep-sea site is necessary.
Signal processing, data handling:
Here two major are the ability to run continuously with a large array of detectors and to
be able to distinguish the neutrino signatures from background sources. Although the
principles of the neutrino signatures are well understood and theoretical algorithms,
e.g. matched filters exist to optimally pull the signatures out of ambient ocean noise
(dominated by wave noise), distinguishing between neutrinos and biologically produced
noise is much more difficult. Currently, substantial data sets exist within the ACORNE
(UK), OnDE-NEMO (Italy) and ANTARES-AMADEUS (EU) collaborations. Preliminary analysis of these data indicates that separating neutrino signatures from other
background sources however, is non trivial. Some techniques that filter data off-line
have been developed for the ACORNE and OnDE-NEMO projects. It is clear however
that we are some time away from being able to define real time triggers for neutrinos.
Efficient trigger techniques are crucial for any acoustics project to keep the data volume
at a manageable level. It is clear that future experiments need to acquire data with equal
or better precision and sampling rate and to run for periods of years. The storing of
such vast quantities of data is challenging as indeed are the mechanisms to share data
between different groups and institutes.
Development of acoustic test sites:
In order to rapidly advance the field of acoustic detection it is necessary to have one or
more suitable deep-sea sites which will act as test benches to assess new technologies,
infrastructures and techniques such as those proposed in the tasks above in as realistic
an environment as possible. The environmental conditions available at the test site
should be as close as possible to those of the final experiment deployment site (deep
sea, permafrost, ice, etc.) and the entire test-site facility should fulfill strong constraints.
A test site facility must be, in fact, equipped with a «hub» laboratory for data acquisition from the experiment and possibly data transfer to the internet; appropriate data/
35.
New techniques for Astroparticle Physics
power cabling systems from the «hub» laboratory to the «in-situ» infrastructure; easy
accessible «in-situ» infrastructure for installation of test devices and systems.Furthermore, the possibility to perform calibration and run tests must be taken into account. At
present, the construction of underwater/ice Cherenkov neutrino telescopes that use the
same neutrino target media, offer a unique opportunity exploit their well-equipped facilities as test-sites for acoustic neutrino detection activities. However, accessibility and
time availability for tests, access to the ‘in-situ’ infrastructure, power and data transfer
systems compatibility must be carefully evaluated.
Studies of material properties.
At highest energies the main problem is to clearly separate the small number of
expected neutrino signal events from the background noise. Large volume in-matter
hybrid arrays using at least two techniques with different systematics could reduce this
problem. Proposed target materials currently under discussion are water, ice, salt and
permafrost. In parallel with the types of studies that have taken place at previouslyproposed optical Cherenkov telescope sites it is important to determine the environmental characteristics at those sites with respect to acoustic detection. Amongst the
important parameters to be measured for corresponding site selections include: signal
attenuation length, noise conditions, efficiency of sensor coupling to material, global
deployment possibilities, hybrid properties and overall cost. For all the detection media
discussed above some environmental studies have already taken place, it is however
necessary to further these studies in order to develop a full picture of the relative merits
of the different detection media and to adapt any future acoustic detection to fully exploit
the medium into which it will be deployed. These studies will culminate in the production
of a compendium of material and site characteristics.
Recommendation and conclusions
Any development of large volume acoustic arrays for neutrino detection is likely
to occur in parallel with the development and deployment of second generation
optical neutrino telescopes in ice and water. This approach will reap immediate
benefits in the form of the sharing of mechanical infrastructure, deployment
costs, provision of power and data transmission. We need to support R&D on
two fronts: one for a detector in ice, the other for a detector in water, which will
address the key issues surrounding the development and ultimate commissioning and operation of such devices.
Contact: Lee Thompson, [email protected]
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New techniques for Astroparticle Physics
3.3.Gas TPC Technology R&D
Credit: drift collaboration
courtesy of the DRIFT collaboration
Gas TPCs, offer exceptional event identification, discrimination and particle tracking,
with additional benefits including room temperature operation and the availability of a
wide range of previous knowledge through the accelerator physics community.
These features make TPC accessible to a wide range of applications, including double
beta decay, neutrino detection, direct dark matter searches and low background
studies.
For dark matter, TPCs offer the prospect of a new generation of detectors capable of
providing information of the direction of WIMP interactions, and hence a tie between
dark matter particles and our motion in the galaxy, the ultimate smoking gun for identification of dark matter.
A new cooperative effort has developed in this area in the last 2 years called CYGNUS
(Cosmology with Nuclear Recoils). This cooperation brings together work by the DRIFT
experiment (UK-US at Boulby), MIMAC (French effort at Grenoble), Spanish groups,
Saclay and theory groups across Europe, to push R&D on TPCs for dark matter.
Although there is significant interest in dark matter TPCs the technology comes to play
elsewhere as well. For instance, there are European efforts to develop novel TPC
detectors for neutron oscillation experiments (such as NOSTOS), for neutron detection (for instance at Modane using He3) for low background assay and interest in solar
neutrino detection and axion detection fields. Recently there has been interest in very
high-pressure gas TPCs for dark matter detection and other work on novel designs with
spherical geometry. These offer room temperature solutions to the use of Xenon, Neon
and other gases currently under development in more complex cryogenic liquid form.
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New techniques for Astroparticle Physics
A key factor in all these is development of advanced electronics, including new chips,
able to readout the necessary multiple channels.
A close link to the particle physics detector groups, for instance in ATLAS at CERN, is
natural for this, to mutual benefit. Related technologies associated with gas TPCs but of
relevance elsewhere are also undergoing growth. In particular, development of Micromegas, GEMs, LEMs and TGEM charge gain devices with prospect for m2 devices,
and associated electronics. Recently Micromegas has been strongly developed and, for
instance, has now been adopted for the T2K experiment in Japan.
Combining simple new charge gain devices such as this with new strip or pixel readout
planes opens prospects for large area track reconstruction with 100 micron position
resolution. Such devices, on a smaller scale, are already in operation in the CAST solar
axion experiment at CERN.
Development of such bulk gas charge readout devices have also applications in Particle
Physics and Astrophysics, in industry including medicine, as well as Astroparticle
Physics. There is interest also in using gas TPCs for homeland security applications
and in assay of alpha-induced memory corruption in computer chips.
There is significant involvement from Russian groups in TPC technology, notably Buzulutskov et al, who have participated in joint R&D programmes with European groups
(Sheffield, Coimbra and others).
Development of charge readout TPC technology in the saturated gas above liquid
phase noble gas targets is also highly important to the current and future generation of
two-phase noble gas detectors being developed for dark matter. This includes ArDM,
WARP and others. The ultimate extrapolation would be for use of TPC technology in
the gas phase above a 100Kton liquid argon detector as proposed by GLACIER for
proton decay and large scale neutrino physics.
R&D priorities: through the CYGNUS cooperation, and wider communication, several
key R&D priorities have been identified as particularly exciting priorities for the next 5
years.
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New techniques for Astroparticle Physics
These are:
1) 2) 3) 4) 5) 6)
7) Acceleration in development of bulk large area charge planes able to reach
10s m2 areas in a low cost, mass production form
Associated development of bulk readout planes towards sub 100 micron
resolution and of novel readout schemes including optical technology with CCD
cameras
Increased understanding, and expansion of, the form and types of gases used,
including negative ion gases and operation in saturated vapour above liquids
Development of fast electronics, including new chips, able to digitize large
numbers of channels, without a trigger
Development toward lower background materials and operation, particularly
study of the effect of radon daughters and their mitigation
Increased understanding of basic physics of gases in TPCs, including much
improved measurement of quench factors, gas parameters vs. pressure and
mixing, gas scintillation and charge transport
Simulations and experiments to establish the limits of low threshold
operation (to sub-KeV level) and track reconstruction in 3D
Recommendation and conclusions
The level of interest in Europe for Astroparticle Physics applications of TPCs
is >25 groups (>100 scientists and students) and increasing. There is worldleading expertise and a wide range of potential experiments that stand to
benefit. A strong and coordinated European R&D programme in TPCs is
essential if this expertise is to be enhanced to the benefit of new, and existing, Astroparticle Physics experiments. Gas Time Projection Chamber technology offers some unique features to Astroparticle Physics experiments
not available through other programmes. We strongly encourage continuation and evolution of an active R&D programme in this area in Europe.
Contact: Neil Spooner, [email protected]
39.
IV
TECHNOLOGIES FROM
ASTROPARTICLE PHYSICS
FOR THE MONITORING OF THE
ENVIRONEMENT AND RISK PREVENTION
Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
Credit: LSM
Gamma-rays spectrometers installed in
the Modane Underground Laboratory
In the following we review three fields of application: atmospheric monitoring, underground monitoring and ocean floor monitoring.
Atmospheric monitoring – overview
The development of the fundamental research in overlapping domains of Cosmology,
elementary Particle Physics and Astroparticle Physics induces ever more demands for
precise measurements.
The new generation of Astroparticle Physics experiments in the field of high energy
cosmic rays, gammas, or neutrinos, are all based on observation of large volumes of
natural media – atmosphere, sea or ice. Thus new experiments designed to provide
demanded measurements have to monitor these media with corresponding accuracy.
The new generation European experiments H.E.S.S. and MAGIC (and VERITAS, based
in the U.S), have opened a new and unique spectral window on the universe. The
number of known very high energy (VHE) photon sources has increased by an order of
magnitude in the last 4 years (from about 10 known in 2003 to almost 100 in 2007).
In ultra-high energy (UHE) cosmic rays, the southern part of Pierre Auger Observatory (PAO), completed in 2008, has already collected more data on particles with energies above 1019 eV than any other experiment, and it is the largest instrument of its
type currently in operation. The Pierre Auger Collaboration recently published the first
observation of the anisotropy of UHE cosmic rays, and has identified active galaxies as
a possible source. This discovery, along with precise energy spectra and constraints
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Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
imposed on chemical composition, is an important first step towards the explanation
of the nature of the enigmatic sources of the most energetic particles in the known
universe and marks the start of a new Astronomy.
The three experiments mentioned above represent a new generation of devices
capable of measuring the fluorescent or Cherenkov light emitted by cosmic rays or
gamma rays with unprecedented precision. However, the experimental teams also have
to perform “new generation” atmospheric monitoring to meet their scientific objectives.
For example, previous UHE cosmic ray experiments concentrated mainly on the
measurement of their energy spectrum. The PAO should also bring information on
the chemical composition of UHE cosmic rays, which will stimulate further theoretical development. Such measurements represent a challenging problem. The
difference between the positions of shower maxima for iron- and proton-induced
showers is comparable to the difference caused by seasonal variations of the atmospheric profile, and this can be blurred even more by rapidly changing atmospheric
aerosol content. Similar problems are encountered with the energy determination of
gamma rays detected with atmospheric Cherenkov telescopes. The aerosol distribution and their attenuation properties are crucial factors in the energy determination of the detected gamma rays, which in turn affects scientific results such as the
measurement of the extragalactic background light produced by the first stars.
All these new generation experiments therefore need to monitor the state of the
air volume observed with higher precision than ever before. The R&D activities in
atmospheric monitoring are led by three major infrastructures that are currently
on-line and are already producing world-class data: PAO, H.E.S.S. and MAGIC.
Smaller projects such as LOFAR or projects with a smaller fraction of European
participation as VERITAS will also benefit. The results and experience gained will
be also used in the R&D for future projects as Auger North or the Cherenkov Telescope Array (CTA), thereby maintaining the European lead in Astroparticle Physics.
Atmospheric monitoring - techniques
To an excellent approximation, the molecular (Rayleigh) and aerosol (Mie) scattering
processes that contribute to the overall attenuation and scattering of light in the atmosphere can be treated separately. The standard method of monitoring of the macroscopic
parameters that determine molecular scattering is based on weather forecasting methods.
They rely on extensive networks of ground stations, frequent (several times a day) radiosoundings and satellite data. All such measurements serve as input to numerical models.
Such extensive meteorological data sampling is not possible at the remote sites of
the mentioned experiments, and the teams have to rely on their own measurements.
The PAO has already managed to produce a provisional local model of seasonal
variation of the atmosphere at the southern Auger site, using Met Office radiosonde
data and their own measurements and other observatories (H.E.S.S., MAGIC) plan
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Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
to follow this example. These average profiles must be produced using systematic
measurements over extended period of time (typically over 2 – 3 years). The goal is to
produce more precise models based on averaged seasonal variations and to develop
methods to account for short-term variation. Therefore, these models together with
further input data from local ground stations operated by the collaborations and from
satellite multi-wavelength data should provide day-to-day predictions of atmospheric
conditions. These have to be checked by LIDAR measurements, star light attenuation
and by radio-sounding. Furthermore, series of radio soundings are necessary to study
the temporal development of humidity. Possible correlations between ground parameters and the shape of atmospheric profiles have to be verified by radio soundings.
Aerosols, compared with the molecular component of the atmosphere, are much more
variable, and can change significantly in the course of a few hours. Because of that, it
has become clear that aerosols are particularly important. Therefore a further aim of this
activity is to determine better the nature of these aerosol populations, and include them
with greater accuracy in computer simulations. The collection of aerosols will require the
construction of various different aerosol collection devices, and their thorough testing
in wind tunnels and in the field. Once the most efficient device(s) have been identified,
experiments will be able to characterize both the types of particles and, crucially, their size
distribution. Measurements will then be made at the H.E.S.S. site in Namibia over a 12-18
month period in order to investigate the seasonality of the atmospheric aerosol loading.
In parallel with this, at times when a particularly high loading of aerosols is detected, radiosondes should be flown in order to investigate atmospheric conditions, particularly wind
speed. This information will be used to improve and extend simulations of the atmosphere.
Apart from multiple scattering effects, transmission due to aerosol scattering may
be fully characterized by three independent measurements: the height profile of the
vertical aerosol optical depth; the wavelength dependence of this aerosol optical depth;
and the normalized aerosol differential scattering cross section, or phase function.
The height profile is usually measured with LIDARs (or more generally with the use of
lasers). For the case of the PAO, one can use not only LIDARs to obtain this aerosol
height profile, but it is also possible to employ directly the cameras of fluorescence
detectors and a calibrated laser beam situated close the centre of the detector area.
The dedicated instruments are then devoted to measurements of the two latter
parameters – wavelength dependence can be measured by the means of observation of terrestrial light source or standard non-variable stars in set of different
filters, and the phase function is measured by observation of standardized beam
of light from various angles. All three of these parameters are already measured
at the Pierre Auger Observatory; however, their analysis is still only preliminary.
Finally, to get complete picture of the immediate status of the atmosphere, one has
also to monitor clouds, their height and (optical) thickness. This can be done either
by dedicated IR cloud cameras or by LIDAR scans, as described below.
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Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
To establish optimized performance of both Cherenkov and fluorescence detectors, it is
also necessary to determine the brightness of the sky background. This can be done using
star monitors or dedicated UV monitors observing in the continuum between 300 and
400 nm and simultaneously using narrowband filters centred on fluorescence emission
lines.
LIDAR techniques
LIDARs provide the most detailed picture of the atmospheric volume observed by telescopes, and at the present time PAO, H.E.S.S. and MAGIC are using or starting to use
single wavelength LIDAR measurements. The wavelength has to be chosen properly
to be sensitive to the most relevant agent in the air, and is usually around 350 nm.
The single-wavelength LIDAR measurements also provide information on the seasonality of aerosol loading. Raman LIDARs will give an even more thorough picture of
the atmosphere. However, this step can be done only after successful implementation of single wavelength LIDAR measurements, performance definition and feasibility
studies. The joint effort of the participating experiments will be particularly beneficial
in this regard. In general, the use of single wavelength LIDARs suffers from the fact
that two physical quantities, the aerosol backscatter and extinction coefficients, must
be determined from only one measured LIDAR signal. This is not possible without
assumptions about the relation between the two and estimate of a boundary or reference value of the aerosol extinction. In Raman LIDAR, the inelastic (Raman) backscatter signal is affected by aerosol extinction but not by aerosol backscatter. Thus,
analysis of the Raman LIDAR signal alone permits the determination of the aerosol
extinction without critical a priori assumptions, and therefore the Raman technique
is of particular interest of all three major participating experiments. At the moment,
there is a prototype of simple Raman LIDAR on the PAO site and there is another,
more sophisticated Raman system in preparation for the use at the MAGIC site.
Atmosphere simulation and modelling
All the experiments measuring Cherenkov or fluorescent light rely on natural atmospheric phenomena to detect radiation of astronomical interest. The amount of light
received from a given ‘event’ is dependent on many things – the energy of the incoming species, the type of initiating particle, the distance of the event from the instrument, atmospheric absorption, the efficiency of the instrument etc. The first two
parameters are of scientific interest, but in order to obtain this information, all the
other parameters which affect the amount of light received must be simulated. The
standard approach is to simulate the particle cascades in the atmosphere to calculate the amount of light emitted, the passage of that light through the atmosphere and,
finally, the performance of the detector. The first of these relies on Particle Physics,
and there are good standard packages available to perform such simulations. Simulation of the instrumental performance is made by each collaboration according to their
own measurements. For the atmospheric part of the simulation chain, collaborations
typically use a range of atmospheric packages, making comparison between simula-
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Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
tions difficult. In addition, these packages have usually been designed for military and
meteorological use, and have many shortcomings for Astroparticle Physics applications.
The aims of experimental teams, therefore, are first to agree a standard basic atmospheric
package to be used for the purposes of comparison. Thus the corresponding R&D should
use the measurements provided by the running experiments in order to produce an atmospheric simulation package that is accurate and suitable for all the experiments to use.
Underground monitoring:
The existence of a set of well-equipped underground facilities in Europe, developed
for Astroparticle Physics searches, allows to develop an interdisciplinary platform
which is ideal for the global observation of our planet and of its immediate surroundings. The development of Astroparticle Physics experiments has been the main
factor driving underground science and technology in general. However, the availability of underground laboratories at the forefront of instrumentation is attracting the
attention of specialists of other fields, in particular environmental and geo-sciences. A
vigorous R&D program is therefore recommendable in this area, with special attention
to radioactive tracers for environmental science, hydro-geological issues, and feeble
magnetic signals, in correlation with seismic phenomena and ionosphere perturbations.
Low radioactive background techniques are becoming more and more interesting also to
other fields of physics research (e.g. physics of the atmosphere, of the environment) as
well as to geology and hydrology. The ultra sensitive detection systems allow for almost
background free measurements and for the determination of ultra low traces of radionuclides. Special relevance has the systematic measurements of C14 and H3 concentrations for geophysical, palaeoseismological and hydrological research projects. Another
very innovative aspect is the set-up of an underground network with accelerometers
and piezometric sensors, which will monitor the deformation phenomena in the laboratories induced by natural and anthropogenic factors, in combination with an already
existing surface-installed network of the same type. This kind of information, never been
acquired before, is important for the understanding of geophysical questions in general.
Moreover, these networks will be used for determining the interactions of water and
rock for a better understanding and more complete interpretation of the environmental
radioactive background (radium geochemistry) and neutron flux analyses (variation of
water content and thus of the neutron spectrum). Furthermore, the radioactive contamination in soil, water, ice and atmospheric dust and particles is very important in order to
characterize many environmental aspects as e.g. transportation phenomena, erosion
and sedimentation.
Another important research field is the geophysical imaging of groundwater resources.
It is relevant to design experiments capable of studying the complex interactions
between tectonic stresses, seasonal infiltration and fault-zone hydromechanical stability.
A major information provided by the crossing of underground laboratory data and natural
45.
Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
cave data will allow to understand the overall functioning of karst aquifers, which represent a significant part of the water resources in the whole Mediterranean region with
large periods devoid of precipitations (up to 6 months). Despite a high demand, these
resources remain under-exploited, due to the lack of knowledge about these systems.
A further stimulating research area is connected to inter-relation between seismic waves
and magnetic perturbations. The arrival of a seismic wave shakes the water-rock interfaces and creates a ionic current generator of magnetic fluctuations characteristic of the
rock environment. In a properly designed underground environment, a very low magnetic
noise environment can be set up, and this perturbation can be identified by its frequency
spectrum and its correlation with seismometer signals. A challenge is to look for a possible
correlation of the amplitude of the collected signals with the hydro-geological situation.
Seismic waves may also be connected to ionosphere perturbations and fluctuations,
which can be detected underground with high signal-to-noise ratio. This is the case for
the double ionosphere response to a P-wave generated by an earthquake. The first
magnetic response is produced at the arrival of P-waves emitted from the epicentre,
at the ionosphere floor. The second magnetic signal is produced again at the ionosphere floor but this time by the arrival at the ionosphere floor of the P-wave emitted
into the atmosphere from the observation site. This second signal is observed only at
large enough distance from the epicentre to allow the first ionosphere excitation to be
detected before the underground travelling time of the P wave to the observation site.
The underground Astroparticle Physics science has induced the development of very
sensitive detectors to measure ultra-low radioactivities for material selection. These
detectors are now used for many applications like environmental measurements, datation (sediments, wine), control of the origin of products. The continuous improvement
of the detectors of ultra-low radioactivity will open new windows for the applications in
the future.
The underground facilities allow also to perform real-time soft-error testing of semiconductor circuits and systems. These errors come from the interactions of neutrons
or alpha rays (from the natural radioactivity of the circuit materials). In the deep underground laboratories, the neutron flux and consequently the neutron contribution are
reduced by at least three order of magnitude, thus in these laboratories the alpha-ray
contribution to the soft-error can be measured.
The previous list of activities in underground laboratories is not exhaustive. Other
fields of science are possibly interested. Per example, the geological storage of
Carbon Dioxide can be studied in-situ to evaluate the response and the evolution of the massif to provide data for the modelisation of this process. The study of
underground live in the rocks or influence of micro-organisms on the hydrology
are other examples of the opportunities of studies for underground laboratories.
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Technologies from Astroparticle Physics for the
monitoring of the environment and risk prevention
Underwater monitoring
The underwater world has not yet been extensively explored. Current technology allows
autonomous vehicles or remotely operated vehicles (ROVs) to carry out scientific experiments at great depths only for relatively short periods requiring costly support ships.
The envisaged large deep-sea neutrino telescope, KM3NeT, will provide abyssal multidisciplinary observatories for deep sea science that will offer a unique opportunity to
explore the properties of deep Mediterranean Sea sites over a period of many years.
The current pilot projects, in the process of constructing deep-sea neutrino telescopes in the Mediterrean Sea (ANTARES-Ligurian Sea, NEMO- East Sicily, NESTORHellenic Sea), are pioneering the development of such permanent undersea
observatories. These facilities already provide real-time, high-bandwidth transmission of continuous measurements of oceanographic (current velocity and direction)
and environmental (temperature, conductibility, salinity, pressure, natural optical and
acoustic noise from sea organisms) parameters from sensors installed on the neutrino
telescope. The installation of specialised instrumentation for seismology, gravimetry, radioactivity, geomagnetism, oceanography and geochemistry provide data
highly attractive for long-term measurements of interest to a wide field of sciences
including biology, environmental sciences, geology, geophysics and oceanography.
Deep sea observatories also have the potential to play a key role in the assessment and monitoring of global warming, climate change and geo-hazards. Many
of Earth’s most seismogenic zones and most active volcanoes occur along continental margins plate boundaries like South Europe. Continuous measurements are
required with the ability to react quickly to episodic events, such as earthquakes
and volcanic eruptions. The destructive earthquakes and related tsunamis that
occurred at the end of 2004 in the Indian Ocean is only the most recent example.
R&D Priorities for underwater monitoring
Development of high-rate data transmission over the large distance from site to
shore (up to 100 km)
Development of low-power consumption electronics and sensors (optical and
acoustic)
Development of cheap and reliable wet-mateable electro-optical connectors
Development of corrosion resistant, pressure tolerant cables and mechanical
structures
Cost effective solutions for the deployment and maintenance of the deep-sea
infrastructure
Contact: J.Ridky, [email protected] // P. Coyle, [email protected]
A.Giuliani, [email protected] // F.Piquemal Fabrice [email protected]
47.
V
CREDITS
Credits
Prepared by:
R. Battiston, G.Chardin, P. Coyle, R. Flaminio, A. Giuliani, J. Marteau,
F. Piquemal, E. Previtali, M. Punch, J. Ridky, N. Smith, N. Spooner, M. Teshima,
L. Thompson, A.M. van den Berg, M. Wurm,
Edited by:
S. Katsanevas, N. Olivier
Graphic design:
Didier Rouable
49.