THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
1 15 September 2011
The Solid State Telescope (SST) instruments: An update on recent
progress in calibration, characterization, and decontamination
Drew L. Turner, Patrick Cruce,
Vassilis Angelopoulos, Victor Kai, and
Davin Larson
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
2 15 September 2011
• SSTs provide the energetic ion and electron measurements for THEMIS and ARTEMIS
• Solid-state detector, collimated telescope design with Al shielding
• 2 SST instruments per spacecraft
• 4 ion and 4 electron “sides” per spacecraft
• Binning logic uses pulse-height analysis and coincidence logic
• SST is known to suffer from significant contamination in the radiation belts
SST Introduction
SST assembly
SST orientation on spacecraft SST-1
SST-2
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
3 15 September 2011
SST X-Section
Attenuator
Foil
Magnet
Detector Stack
Attenuator
Foil Collimator
Open Collimator
Attenuator
Foil
Magnet
Detector Stack
Attenuator
Foil Collimator
Open Collimator
Open Side (ions)
Open Side (ions)
Foil Side (electrons)
Foil Side (electrons)
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
4 15 September 2011
Foil Collimator
Thick Detector
Sm-Co Magnet ~1kG reflect electrons < ~300 keV
Attenuator (stops electrons < ~800 keV)
Al/Polyamide/Al Foil (4150 Ang thick –stops Protons < ~350 keV) Open Detector
Foil Detector
Attenuator
Open Collimator
electrons (>25 keV)
ions electrons
ions
Electron (Foil) Side Ion (Open) Side
SST Operations Concept
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
5 15 September 2011
• With a stack of 3 detectors there are 7 types of events: – F - Single event in Foil detector (electrons < 600 keV, protons > 350 keV) – O - Single event in Open detector (protons < 6 MeV, electrons > 300 keV) – T - Single event in Thick detector (X-rays, shield-penetrating electrons and
secondary’s) – FT – Coincident events in Foil & Thick (electrons 335 -800 keV) – OT – Coincident events in Open & Thick (protons > 6 MeV) – FTO – Triplet event – (electrons > ~1MeV, protons > 10 MeV?) – FO - Treated as separate F and O events.
• Of the 16 energy channels per species, the first 12 record singlet events, and the last 4 record coincident events
• In the radiation belts: ALL channels are sensitive to shield-penetrating electrons (> ~1 MeV)
SST Logic
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
6 15 September 2011
• Saturation in channels at count rates >20 kHz
• Cross-contamination
• Shield- and attenuator-penetrating particles
• Sunlight contamination (Open sides)
• Dead layers on detectors
• Channel cross-talk (electronics)
• SSTs were never fully characterized or calibrated, but we have recently made great progress towards fully understanding this important dataset!
SST Challenges
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
7 15 September 2011
• Geant4 is CERN-developed software used to characterize energetic particle interactions with matter
• Using a simplified geometry, we have characterized the signal and cross-contamination efficiencies for electrons and protons from 20 keV – 10 MeV
• More complex model in development for background characterization
10x 100 keV electrons incident down centerline on foil side
10x 1 MeV electrons incident down centerline on foil side
SST Characterization
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
8 15 September 2011
0 1000 2000 3000 4000 5000 6000 70000
0.1
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0.9
1
Incident Energy [keV]
Effic
iency
Protons Binned Efficiencies from Open Side Field of View
Open 1Open 2Open 3Open 4Open 5Open 6Open 7Open 8Open 9Open 10Open 11Open 12Open Thick 1Open Thick 2ThickFTO LowFTO Hi
0 100 200 300 400 500 600 700 800 900 10000
0.1
0.2
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0.4
0.5
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1
Incident Energy [keV]
Effic
ienc
y
Protons Binned Efficiencies from Open Side Field of View
Open 1Open 2Open 3Open 4Open 5Open 6Open 7Open 8Open 9Open 10Open 11Open 12Open Thick 1Open Thick 2ThickFTO LowFTO Hi
Note: Responses in Foil channels are null
Proton Response Functions
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
9 15 September 2011
0 200 400 600 800 1000 1200 1400 1600 1800 20000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Incident Energy [keV]
Effic
iency
Electrons Binned Efficiencies from Foil Side Field of View
Foil 1Foil 2Foil 3Foil 4Foil 5Foil 6Foil 7Foil 8Foil 9Foil 10Foil 11Foil 12Foil Thick 1Foil Thick 2Foil Thick 3FTO LowFTO Hi
Note: Responses in Open channels are null
Electron Response Functions
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
10 15 September 2011
Efficiencies Applied to Data
Old Data: All effs. = 1.0 and wrong electron Ebins
New Data: Effs. and Ebins from Geant4
Inner Belt Slot Outer Belt
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
11 15 September 2011
• Electrons get through the magnet starting at ~300 keV: we need to calculate energy-specific geometric factors to account for this
Cross-Contamination
• Protons get through the foil at ~350 keV
• We have run Geant4 for these configurations as well to get X-contamination efficiencies
• Since we measure this range of energies, decontamination is achievable
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
12 15 September 2011
• All channels are affected by shield- and attenuator- penetrating electrons > ~1MeV
Background Contamination
• Efficiencies are small, but GFs are orders of magnitude larger than those for the signal
• These can explain the upside-down E-spectra in outer belt:
Note: the higher open (and foil) and FTO channels are most affected
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
13 15 September 2011
• Coincidence channels: FT not affected by proton contamination AND FTO measures >1 MeV electrons!
• These can be used for decontamination and background removal
Coincidence Channels
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
14 15 September 2011
• We are investigating a matrix solution for X-contamination and background removal
Decontamination
Mi,k ! jkTrue + fi ! j
FTO = ciMeas.
fi =GFTO!i
FTO
Measured Counts X-Contam. Matrix Clean Flux
Mi,k =
GCe1Je1!Ce1Je1 … GCe1Jen
!Ce1Jen GCe1Jp1!Ce1Jp1 … GCe1Jpm
!Ce1Jpm! " ! ! " !
GCenJe1!CenJe1 … GCenJen
!CenJen GCenJp1!CenJp1 … GCenJpm
!CenJpmGCp1Je1
!Cp1Je1 … GCp1Jen!Cp1Jen GCp1Jp1
!Cp1Jp1 … GCp1Jpm!Cp1Jpm
! " ! ! " !GCpmJe1
!CpmJe1 … GCpmJen!CpmJen GCpmJp1
!CpmJp1 … GCpmJpm!CpmJpm
!
"
########
$
%
&&&&&&&&
Electrons X-Contam.
Electrons Signal Protons X-Contam.
Protons Signal
Background geometric factors (G) and efficiencies (ε)
Background
For “n” electron (e) channels and “m” proton (p)channels; i = k = n + m
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
15 15 September 2011
• Important for accurate PADs
• Calibration during quiet conditions with near-isotropic distributions – PADs are fit to an even cosine function
– Available in latest bleeding edge software
– Caveat: before 12 Dec. 2007 is “special”
Inter-Anode Calibrations
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
16 15 September 2011
• We are developing a technique to get absolute calibration factors for the SST fluxes from each spacecraft
• SST will be calibrated to ESA, which have been inter-calibrated amongst spacecraft
• Ongoing work; this requires fully decontaminated data
Absolute Calibrations
ESA SST ESA SST
NOTE: These results are not calibrated and use the new SST efficiencies and energy limits
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
17 15 September 2011
Preparing for RBSP
• Moving ahead: THEMIS, with newly calibrated SSTs, will allow for complementary science with RBSP:
– Fields and waves
– Thermal plasma
– Energetic particles, incl. relativistic electrons
• RBSP/GEO/THEMIS covers full range of the belts and into the source region
• THEMIS-SST will provide key, energetic particle measurements to address RBSP science objectives!
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
18 15 September 2011
• THEMIS, with newly calibrated SSTs, will allow for complementary science with RBSP
– PSD for fixed 1st and 2nd invariants beyond GEO
– Radial and pitch angle distributions throughout the outer belt at higher time cadence (think multiple strings of pearls)
– Magnetic local time variations
– Plus additional wave observations beyond GEO
Preparing for RBSP
From Turner et al. [2011]
Mu [MeV/G]"
NOTE: These profiles are notably consistent with those from POES >300 keV electrons
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
19 15 September 2011
• Significant progress has been made in characterizing, calibrating, and decontaminating SST data
• Work is ongoing, but a new, clean SST dataset will be ready for the RBSP era
• Background, cross-contamination, and signal response functions are consistent with intercalibration factors found by Ni et al. [2011] with LANL-GEO
Conclusions
From Ni et al. [JGR, 2011]
• THEMIS spacecraft traverse the radiation belts at least 6 times each day and also sample the important source population beyond the last closed drift shell
• THEMIS-SST will provide key, energetic particle measurements to complement the RBSP dataset and address RBSP science objectives!
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
20 15 September 2011
• Backups
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
21 15 September 2011
New Energy Channels
Channel Elow (keV) Ehi (keV)
Eeq. (keV)
Foil-1 26 36 31
Foil-2 36 46 41
Foil-3 46 58 52
Foil-4 58 73 65
Foil-5 73 113 91
Foil-6 113 165 137
Foil-7 165 242 200
Foil-8 241 345 288
Foil-19 345 495 413
Foil-10 495 600 545
Foil-11 -- -- --
Foil-12 -- -- --
FT-1 335 481 401
FT-2 481 642 556
FT-3 640 799 715
FTO-1 >710 -- ~1000
Channel Elow (keV) Ehi (keV)
Eeq. (keV)
Open-1 25 37 30
Open-2 36 48 42
Open-3 46 65 55
Open-4 59 77 67
Open-5 75 116 93
Open-6 115 175 142
Open-7 168 245 203
Open-8 243 348 291
Open-19 346 494 413
Open-10 492 813 632
Open-11 812 1455 1087
Open-12 1453 6500 3073
OT-1 6315 6485 6400
OT-2 -- -- --
Thick-1 -- -- --
FTO-2 -- -- --
Electron Channels Proton Channels
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
22 15 September 2011
Saturation
NOTE: According to Davin, saturation should start to occur around 20,000 counts/sec
THEMIS/ARTEMIS SWG Meeting Annapolis, MD
ARTEMIS
THEMIS
23 15 September 2011
Sunlight Contamination
NOTE: The contamination is mostly removed from ion spectra, though there is still a residual which should be accounted for in PADs!
Sunlight contamination is most evident in spin angle flux spectra because Sun-direction is fixed over short periods
In electron spectra, “sunlight” contamination is really due to X-talk on the channels
Automated sunlight removal works very well for electrons
ORIGINAL PROTON DATA
CORRECTED PROTON DATA
CORRECTED ELECTRON DATA
ORIGINAL ELECTRON DATA