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Solar Energetic Particle instrument Front end/sensor Pre-PDR peer review

Solar Energetic Particle instrument Front end/sensor Pre-PDR peer review. Davin Larson, Rob Lillis, Ken Hatch, David Glaser David Curtis UCB. SEP instrument overview.

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Solar Energetic Particle instrument Front end/sensor Pre-PDR peer review

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  1. Solar Energetic Particle instrumentFront end/sensor Pre-PDR peer review Davin Larson, Rob Lillis, Ken Hatch, David Glaser David Curtis UCB

  2. SEP instrument overview • The Solar Energetic Particle (SEP) instrument measures the energy spectrum and angular distribution of solar energetic electrons (30keV–1 MeV) and ions (30 keV-12 MeV). Foil Detector Al/Polyamide/Al Foil (stops ions <350 keV?) Thick Detector Open Detector Electrons Ions Foil Collimator Open Collimator Attenuator Attenuator Sm-Co Magnet (sweeps away electrons <350 keV)

  3. Sensor Units • Each sensor unit is a: • Dual-double ended solid state telescope • Each double ended telescope (1/2 sensor) has: • Triplet stack of silicon solid state detectors • Foil (on one side) • Filters out ions <~200 keV? • Leaves electron flux > ~20 keV nearly unchanged • Magnet / Open side • Filters out electrons <350 keV • Leaves ion flux nearly unchanged • Mechanical Pinhole attenuator • Reduces count rate during periods of high flux • Reduces radiation damage (caused by low energy ions) during periods of high flux • Collimators • Preamplifier / shaping electronics

  4. Sensor Cross Section Foil Collimator Attenuator Foil Detector Stack Magnet Attenuator Open Collimator

  5. Location of SEP Sensors and Fields of view (FOVs). APP REVISED SEP FOVS

  6. APP Sweep Volume PLENTY OF CLEARANCE TO ACCOUNT FOR REQUIRED APP SWEEP VOLUME CHANGES NEW SEP FOVS APP SWEEP VOLUME APP SWEEP VOLUME MUST BE INCREASED SOME TO ACCOUNT FOR CHANGES FROM IUVS AND STATIC

  7. Changes from THEMIS SST Sensor design • Foil is closer to detector stack: 0.73 cm → 0.19 cm. • Higher % of electrons scattering in foil reach detector. • Foil thickness may decrease from 4.3 µm to 2 µm. • Detection of electrons down to ~20-25 keV (previously 30 keV). • Allows better cross calibration with SWEA and SWIA. • Increased geometric factor: 0.1 → 0.155 cm² sr • Detector area is 17% bigger: 0.92 cm² → 1.08 cm² • FOV has expanded from 40° x 23° to 40° x 31.5° • Detector casing was formerly PEEK, now brass. • Better radiation protection.

  8. Changes from THEMIS SST Electronics design Electronics is now on 2 boards (instead of one) Each board is independent with 6 channels (one sensor) Separate bias supplies - FPGAs Switch preamplifier from Amptek 225FB to 250F New pulse shaping chain (similar characteristics -2.5 us) Separate test pulsers for each chain. Add ADC for analog housekeeping. Add 3.3 Volt digital line to reduce power. Switch diodes in bias supply No longer sensing attenuator position. Switch to dual MDM connectors on DFE No more internal thermostat or internal heater Adding Burst capability to FPGA

  9. Moving foil closer to detector. Rationale: electrons scatter in the foil & can miss detector. CASINO simulations

  10. Foil thickness is a science trade-off • We would like to extend our energy range as low as possible for greater overlap with SWIA and SWEA. • What are the consequences of thinner foils? • Pro: buys several keV. • Con: lower energy protons penetrate

  11. Electron transmission through foils:

  12. Proton energy loss in foil depends on thickness

  13. Expected fluxes & SEP detector count rates • Without attenuation, protons may saturate the detector during the very largest events. • Below are representative spectra and count rates.

  14. SEP Detector Stack Assembly DFE Board Subassembly BeCu Gasket (3) Detectors (4) KaptonHeater Spring Clamp PEEK Spacer (4) Spring Plate (2) Kapton Flex-Circuit (4) AMPTEK Shield Thermostat Detector Board Composition (exploded view)

  15. Electronics Block Diagram • Signal chain: 1 of 12 channels shown Bias Voltage Test Pulser DAC Gain + shaping Thresh FPGA Coincidence Logic & Accumulators PD A250F Preamp Shaper ADC Memory BLR DFE Board DAP Board

  16. THEMIS SST preamp design • Using Amptek 225FB (6pin sip Hybrid - special request) • Characteristics: • ~6 keV electronic noise (with 1.5 cm2 detector) • ~2.5 uS shaping time (time to peak) • ~26 mW (Increases with negative supply voltage) • 100 Krad (still needs ~3mm Cu shield) • Operating range: -55 to +125 C • Dual supply allows negative output pulses B

  17. Preamp design changes for MAVEN SEP • Using Amptek 250F (6pin sip Hybrid) • Characteristics: • ~2 keV electronic noise (with 40 pF detector) • ~2.5 uS shaping time (time to peak) • 100 Krad (still needs ~3mm Cu shield) • Operating range: -55 to +125 C • Dual supply allows negative output pulses • Different pinout!

  18. Detector Pixelation • Detectors similar to STEREO/STE • Produced at LBNL/Craig Tindall PI Active area 7 mm Guard ring 13.2 mm THEMIS SST & MAVEN EM

  19. Detector Pixelation • Detectors similar to STEREO/STE • Produced at LBNL/Craig Tindall PI Active area 8.2 mm Guard ring 13.2 mm MAVEN SEP

  20. -35 V THEMIS SST Design ~200 A Polysilicon +4.5 V F n F Out p 225FB -2.5 V Pixelated side ~1200 A Dead layer F Test in p n T T Out 225FB n p T Test in O p O Out 225FB n Outside Grounded O Test in ~200 A Polysilicon + ~200 A Al 300 micron thick detectors

  21. MAVEN SEP Design -35 V ~200 A Polysilicon +5 V F n F Out p 250F -5 V Pixelated side ~1200 A Dead layer F Test in p n T T Out 250F n p T Test in O p O Out 250F n Outside Grounded O Test in ~200 A Polysilicon + ~200 A Al Protection Diodes Added too 300 micron thick detectors

  22. Sun in FOV for SEP • SEP FOVs • 2 SEP sensors with 4 apertures per sensor (only 2 of 4 apertures on each sensor are light sensitive) • 1 actuator closes all 4 apertures • Constraints on commands to SunSafe SEP • Takes ~ 200-500 ms (Temperature dependent) to close doors • SEP actuator must wait 15 seconds before it is re-actuated • SEP uses a status switch • Spacecraft needs positive confirmation of safing • Cannot damage SEP by sending multiple commands • Current actuator life tested to 70,000 cycles • Need to evaluate if this will be sufficient • SEP requires power to close actuators

  23. Backup slides

  24. Level I requirement: • MAVEN shall determine solar energetic particles (SEP) characteristics, 50 keV to 5 MeV protons, with ~1 hr resolution characteristics of SEP events. Requires energy resolution better than 50%; accuracy better than 30%. • Rationale: • SEPs precipitating into the martian atmosphere provide energy input that contributes to controlling upper-atmospheric processes, and may provide a direct driver of loss of atmosphere to space.

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