the solid state telescope (sst) instruments: an ... -...

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


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


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)


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


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


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


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


ARTEMIS

THEMIS

8 15 September 2011

0 1000 2000 3000 4000 5000 6000 70000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1


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


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


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


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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


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!


ARTEMIS

THEMIS


•  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


ARTEMIS

THEMIS


•  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!


ARTEMIS

THEMIS


•  Backups


ARTEMIS

THEMIS


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


ARTEMIS

THEMIS


Saturation

NOTE: According to Davin, saturation should start to occur around 20,000 counts/sec


ARTEMIS

THEMIS


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

the solid state telescope (sst) instruments: an ... -...

Documents