1. THEMIS SRR 1 UCB, June 8-9, 2003 Solid State Telescope Davin Larson SSL

2. THEMIS SRR 2 UCB, June 8-9, 2003 Overview Requirements –Science Requirements –Performance Requirements Basic Design Capabilities

3. THEMIS SRR 3 UCB, June 8-9, 2003 SST Science Requirements SST-1: The SST shall perform measurements of the tailward- moving current disruption boundary speed using the finite gyroradius technique (4.1.1.2, 4.1.1.5). SST-2: The SST shall measure the time-of-arrival of superthermal ions and electrons of different energies emanating from the reconnection region to determine the Rx onset time (4.1.1.3, 4.1.1.5). SST-3: The SST shall compute the partial energy moments due to the superthermal ions and electrons in the magnetotail plasma sheet (4.1.1.3, 4.1.1.6, 4.1.1.7, 4.1.1.9, 4.1.1.10). SST-4: The SST shall obtain measurements of ion and electron distribution functions with one spin time resolution (<10sec required) (4.1.1.2, 4.1.1.3). SST-5: The SST shall measure energetic electron fluxes as close to Earth as 6RE geocentric, at all local times. (Radiation belt science- tertiary objective – achieved by nominal design). SST-6: The SST shall measure energetic ions in the solar wind, at the magnetopause and in the magnetosheath (Dayside science – secondary objective – achieved by nominal design).

4. THEMIS SRR 4 UCB, June 8-9, 2003 SST Performance Requirements SST-7: The SST shall measure energetic particles over an energy range of 30-300keV for ions and 30-100keV for electrons found in the magnetotail plasma sheet (SST-1, SST-2). SST-8: The SST energy sampling resolution, dE/E, shall be better than 30% for ions and electrons (SST-1, SST-2). SST-9: The SST shall be capable of measuring differential energy flux in the range from: 10^2 to 5x10^6 for ions; 10^3-10^7 for electrons (keV/cm2-s –st- keV) whilst providing adequate counts within a 10 second interval. (exact values TBD) (SST-1, SST-2) SST-10: The SST shall measure over 90 o in elevation with a minimum resolution of 45 o (SST-1, SST-2, SST-3, SST-4). SST-11: The SST shall have an azimuthal resolution of 45 o (SST- 1, SST-2, SST-3, SST-4). SST-12: The SST shall supply the high energy partial moments at one spin time resolution (SST-3) SST-13: SST calibration shall ensure <20% relative flux uncertainty over the ranges defined above (SST-1, SST-2).

5. THEMIS SRR 5 UCB, June 8-9, 2003 SST Sensor Unit Each sensor unit is a dual-double ended telescope with 2 oppositely directed look directions for electrons and 2 for ions. (2 units/ spacecraft provide 4 look directions / species) Magnet 3 PIPS Detectors Parylene foil SST THEMIS Electrons Ions

6. THEMIS SRR 6 UCB, June 8-9, 2003 SST Design changes The original design: WIND-like sensors with the ESTEC PDFE chip. 3 look directions for each species (0 o, +36 o, -36 o ). Spin plane (0 o ) had additional low geometric factor (10%) detector. Geometric factors same as WIND. e-e- i+i+ 19”x7” panel

7. THEMIS SRR 7 UCB, June 8-9, 2003 SST Basic Design New Design Now have 4 elevations angles for each geometric factor (instead of 3 elevations for high GF, 1 for low GF) Increased dynamic range for all look directions. Simpler design allows some mass savings. Preamps located very close to detectors allows low noise measurement. 19”x7” panel (Remainder of S/C not shown)

8. THEMIS SRR 8 UCB, June 8-9, 2003 SST Block Diagram SST Sensor Block Diagram (1 of 10 channels shown) ADC FPGA Coincidence Logic & Accumulators Memory DAC Thresh Gain PD BLR To DPU A225F Preamp Shaper Det/Preamp Board ADC BoardACTEL Board Test Pulser Bias Voltage

9. THEMIS SRR 9 UCB, June 8-9, 2003 SST Block Diagram To Processor Sensor Unit Sensor Unit Formatter/ Moment Computer (1 ACTEL) (In IDPU)

10. THEMIS SRR 10 UCB, June 8-9, 2003 SST Capabilities Capabilities: Amptek 225F has ~6 keV noise (with 1.5 cm 2 detector) this will give <18 keV threshold for electrons (slightly higher threshold for ions due to dead layer). Each outer detector has two active areas (ratio: x100) for dual geometric factor response. Each active area has a separate electronics chain that can be powered off. Dynamic range of combined system should be >10^6 Thick inner detector will measure electrons up to ~1 MeV and ions up to >12 MeV Foil / Magnet system used to stop electrons and ions <400 keV.

11. THEMIS SRR 11 UCB, June 8-9, 2003 Design Changes Under Study: Solid State Detectors are sensitive to radiation damage. In particular, the very high flux of low energy (<100 keV) ions can change the energy calibration of the ion detectors over time (presumably by changing the thickness of the dead layer). The electron detectors are not sensitive to this problem because the foil will stop these ions. Difficult to calibrate in flight without flying a radiation source. Possible Solution: Use mechanical door (shutter) to reduce the entrance aperture during high flux periods thus reducing the total accumulated ion flux. ~25 gm/door. Simultaneously solves dynamic range problem. Eliminates need for separate low geometric factor electronics chain. Only needed on the ion detectors.