Download EUS REVIEW TO PPARC JAN 2004 (Harrison)

An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Solar EUV spectrometer – to identify & analyse emission lines from trace
elements in the solar atmosphere, providing plasma diagnostic information for
many applications – it is a general purpose solar plasma diagnostic tool!
 Builds on the highly successful RAL-led SOHO/CDS – just completed its 8th
year of operation – and UK strengths.
 The use of such a ‘facility’ is well
illustrated by the exploitation of CDS:
14 UK user groups - 50 world-wide;
24 hour a day operation run through a
request ‘diary’; 550 papers.
 Serves active, world-class UK solar
community – solar atomic physics,
fundamental processes and solar activity.
CDS observation of twisted flows in a loop
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Solar Orbiter provides a completely new view of the Sun – with numerous
close encounters and high latitude observations.
 Mission firsts:
Explore the uncharted innermost regions of
our solar system;
Study the Sun from close-up (45 solar radii);
Fly by the Sun tuned to its rotation and
examine the solar surface and the space
above from a co-rotating vantage point;
Provide images of the Sun’s polar regions
from heliographic latitudes in excess of 30°.
Solar Orbiter
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Mission goals:
Determine the properties, dynamics and interactions of plasma, fields and
particles in the near-Sun heliosphere;
Investigate the links between the solar
surface, corona and inner heliosphere;
Explore, at all latitudes, the energetics,
dynamics and fine-scale structure of the
Sun’s magnetized atmosphere;
Probe the solar dynamo by observing the
Sun’s high-latitude field, flows and seismic
waves.

Three of these require EUV spectroscopy.
Solar Orbiter
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Strawman payload – as defined by PWT
Instrument
Mass
kg
Power
W
Rate
kbps
Plasma Package (SWA)
15.5
11
14
Fields Package (MAG +RPW + CRS)
11
13
5.8
Particles Package (incl. Neutrons,gammas &
dust)
15
15
4.5
Visible Light Imager & Magnetograph (VIM)
30
25
20
EU Imager (3 telescopes incl. FSI)
30
25
20
EU Spectrometer
25
25
17
Spectrometer/Telescope Imaging X-rays (STIX)
4
4
0.2
Coronagraph (COR)
10
10
7
Total
140.5
128
88.5
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 The need for a spectrometer...
 This is the best we can do now: EUV imaging to 0.5 arcsec (350 km) and
EUV spectroscopy to 2-3 arcsec. We know that the solar atmosphere is
composed of fine-scale structures and must aim to develop appropriate tools.
Our target is spectroscopy at ~70 km (0.5 arcsec at 0.2 AU, 0.1 arcsec at 1 AU).
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 The need for a spectrometer... exploring the physics of the
solar atmosphere:
 Polar flows and coronal hole evolution –
unique aspect of the polar regions;
 Fundamental small-scale processes at all
latitudes – true spectroscopy with resolutions an
order of magnitude better than now;
 Linking coronal and heliospheric structure and
events –
correlation of
close proximity
in-situ data with
remote sensing
plasma
parameters.
A spiralling plasma jet
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 The need for a spectrometer... exploring the physics of the
solar atmosphere:
 High resolution imaging reveals fine-scale structure beyond current
spectroscopic capability (350 km vs 1500 km).
 Filling factor spectral studies reveal even more fine-scale structure, beyond
current imaging capabilities.
 Need order of magnitude improvement to
address fundamental scales:
Loop fine-scale structure <350 km
Proton mfp in corona ~750 km
Granular sizes ~ 1000 km
Supergranular cell size ~30000 km
Explosive event/blinker scales ??
Scale heights ~ 500 km in chromosphere;
5000 km in TR and 50,000 km in corona
Fine-scale loops detected using TRACE
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 EUS instrument requirements...
Spatial Resolving Element (pixel)
Spectral Resolving Element (pixel)
Field of View (minimum)
Exposure time (minimum)
Maximum Exposure Time
Wavelength Bands
Pointing
0.5 arcsec
75 km at perihelion
0.01-0.02 Å/pixel lower the better
34 x 34 arcmin2
AR size at perihelion
<1 s
Few 100 s
cosmic ray limit
170-220 Å
Prime bands from
580-630 Å
Tenerife meeting
> 912 Å
To anywhere on Sun and low corona
(1) Science Definition Team - resolution requirement may be relaxed to 150 km target.
(2) Spectral resolution - critical driver - polar flows.
(3) Wavelengths – lines from chromosphere, transition region & corona is a major driver.
(4) Pointing – payload bolted together, common pointing JOP approach.
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 EUS instrument plans
 Next-generation CDS led from RAL proposed at PPARC SOI;
 Proto-consortium has met four times – in 2001, 2002 and 2003, and
dedicated wavelength meeting in 2003;
 Pre-proposal to PPARC - end of Oct. – consortium includes UK solar
hardware groups at RAL, MSSL and Birmingham (SMM, CHASE, Yohkoh,
SOHO, Solar-B, STEREO…)
 Consortium Web site - http://www.orbiter.rl.ac.uk:
1. Concept document (‘Blue Book’)
2. Technical studies e.g. Wavelength selection; Orbiter goals; Optical design
requirements; Detector requirements
3. Meeting reports, including ppt talks.
4. Contacts, links, mission notes/documents...
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 EUS instrument concept & initial design strategy...
 Two design concepts now under discussion
 Off-axis single mirror NI telescope with VLS grating
 Wolter II GI telescope with VLS grating
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Other factors which influence the design
Instrument Size
Mass
Telemetry
Max. Length 2.0 m
25 kg target
20 kbit/s target
Power
Thermal Environment
30 W target
Varying and high levels of
heat
input
requiring
careful control .
Varying levels of particle
events with some extreme
‘storms’. Includes solar
neutrons.
Particle Environment
Autonomy
Optical Correction
Due to spacecraft size
Under 30 kg
Demands large on board
memory
Due to solar proximity and
eccentric orbit.
Cosmic rays similar to
SOHO but solar events
more extreme. 25x solar
wind flux. Must be able to
cope with latch-up.
Pre-planned sequences in No contact for solar
deferred command store.
passes
May require active image Spacecraft stability to be
stabilisation system.
defined.
An EUV Spectrometer for the ESA Solar
Orbiter Mission
Thermal Loads
 149 day cycle = 2,142 to 34,275 W/m2 (0.8 to 0.2 AU).
 Need to address thermal balance for high load values and for variation
of thermal input.
 We must validate the designs through extensive modelling.
An EUV Spectrometer for the ESA Solar
Orbiter Mission
Particle Environment at 0.2 AU
 Cosmic Rays:- Non-solar cosmic rays about the same as for SOHO, or less.
 Solar Wind:- Projecting from 1 AU (~10 p/m3), might expect 250 p/m3 in quiet
conditions, with v ~ 400 km/s. Thus, we expect 106 hits/cm2.s (25x SOHO flux).
 Neutrons:- 15 min half life means that we may expect them. Concern over their
cross section at the silicon lattice relative to protons. Needs investigation.
 Flares and shock (CME) particles:- Dose difficult to predict. May be more
events than SOHO. Events 25x stronger.
Note: Hadrons can cause damage to a CCD silicon lattice which causes traps
that can ‘steal’ charge which can be transferred to other parts of the image.
Note: What about particle effects on optical surfaces?
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Thermal-Mechanical Issues
 Mass allocation for payload under 140 kg. Allocation for spectrometer <30
kg (CDS 100 kg, EIS 60 kg)
 CFRP option and SiC option being studied with initial mass breakdown in
Payload Definition Document – strategy includes low-mass detector option,
no pointing system…
 In parallel, second phase of thermal modelling (149-day prime orbit, 0.2 to
0.8 AU – 34,275 to 2,142 Wm-2)
 Thermal strategy – off-axis = heat stop, primary radiator, with active
‘smoothing’ of extremes using heat switches…
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Detectors
 Particle environment rules out CCD detector approach
 4k x 4k 5μm pixel array currently baselined (precludes CCD option)
 Low mass option – on-chip electronics
 Conclusion: Active Pixel Sensor option (RAL/E2V)
APS detectors are being suggested for a range of Solar Orbiter instruments,
including the EUV spectrometer, EUV imager and coronagraph – and have
advantages for a range of future missions, not necessarily solar oriented.
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Detectors
APS Detectors:
 Silicon image sensor with pixels.
 Wavelength coverage same as a CCD.
6 inch wafer
Single die
 Difference - charge sensed inside the pixel.
Advantages . . .
 Smaller CMOS processing geometry:
Smaller pixels = Smaller instruments.
Wire-bonded to a PCB
10Hz Test Image
 CMOS allows on-chip readout circuitry:
Low mass, low power cameras.
 No Large scale charge transfer: More radiation tolerant than a CCD.
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Detectors
Progress at RAL/E2V:
 512x512 25μm pixel prototype constructed
and backthinned.
 4k x 3k 5μm pixel prototype now
developed. Backthinning procedures under
development now.
n
N Well
n+
n
P Epitaxial Layer
n
P Well
n
Readout
Transistors
3 m thick
Photodiode
P Substrate
Etch away
~ 1000 m thick
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 The consortium – building on the SOHO strengths
Rutherford Appleton Laboratory, UK
Mullard Space Science Laboratory, UK
Birmingham University, UK
Max Planck, Lindau, Germany
Padua University, Italy
Goddard Space Flight Center, USA
Oslo University, Norway
A prominence eruption detected using CDS
IAS, Orsay, France
NRL, Washington, USA
Scientific Co-I Groups – e.g. Armagh, Aberystwyth, Cambridge, Glasgow,
Imperial College, St Andrews, Strathclyde, UCLAN, Catania, Florence …
An EUV Spectrometer for the ESA Solar
Orbiter Mission
 Solar Orbiter History – UK interest
 ESA Solar Physics Planning Group & First Tenerife Meeting (1998)
 ESA Pre-Assessment Study (1999)
 Statement of Interest (Jan 2000) & Delta ‘Study’
 Proposal (July 2000) & Presentation to ESA Committees (Sept 2000)
 Selection as F-mission (Oct 2000)
 Payload Working Group (Remote Sensing) (2002/3)
 Science Definition Team (2003)
 ESA programme ‘reconstruction’ (2003) – reconfirmed!