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Instrument Design: STEIN

Instrument Design: STEIN. Jasper Halekas and Davin Larson Kyung-Hee Visit October 2009. Space Physics Instrumentation. Usually want to: Maximise sensitivity Maximise energy/angular resolution and coverage Minimize weight/power

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Instrument Design: STEIN

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  1. Instrument Design: STEIN Jasper Halekas and Davin Larson Kyung-Hee Visit October 2009

  2. Space Physics Instrumentation • Usually want to: • Maximise sensitivity • Maximise energy/angular resolution and coverage • Minimize weight/power • Separate different species of charged particles (and sometimes neutrals!)

  3. Electrostatic Analyzer • Separates species very well, has very good energy/angular resolution • Low sensitivity, because of small geometric factor and need to sweep energy/angle • Can only measure one species in each detector

  4. STEREO STE (SupraThermal Electrons) • Prototype detector • Very good sensitivity • Measures all energies simultaneously • Can measure ions, electrons, neutrals • But - have to have some way to separate species! • Thin window detector, very sensitive electronics, allows measurements to a few keV • (few keV low energy threshold unprecedented for solid state detectors!)

  5. Parker Spiral Electrons Solar Wind Ions STE-U STE-U w/FOV and Preamp Mounts to side of IMPACT Boom Field of view along Parker spiral – with solar wind out of FOV 70x70 STE-U FOV

  6. THEMIS SST Energy range > ~20 keV, electrons and ions separated

  7. Basic design of SST instrument Foil Detector Al/Polyamide/Al Foil (stops ions <400 keV) Thick Detector Open Detector Foil Collimator Open Collimator Attenuator Attenuator Sm-Co Magnet (sweeps away electrons <400 keV)

  8. Foil Separation

  9. Toolchest 1: Interactions w/ Matter CASINO = " monte CArlo SImulation of electroN trajectory in sOlids "

  10. X Magnetic Deflection B = 500 G 1 cm 2 cm X 2 cm pixelated (8x8) detector • Energy Range 2 keV – 50 keV (full angular coverage), Angular Range ±30°. • Partial angular coverage for higher energies. • Poor angular resolution for lowest energies.

  11. Magnetic Deflection

  12. Magnetic Deflection

  13. Toolchest 2: Finite Element Magnetostatics • Define a discrete grid and solve for the magnetic potential from each element • Linghua Wang used a commercially available program for this work

  14. Toolchest 3: Tracing Particles The Lorentz Force Law provides the second order differential equation of motion for charged particles. We use the 4th order Runge-Kutta method with an adaptive time step to solve this ordinary differential equation

  15. 4 3 2 1 Electrostatic Deflection 2 cm E-Field Region Electrons Ions 2 cm W L

  16. Top View 5 cm 2 cm Ions High Energy Ions and Electrons 3 cm 4 mm Electric Field Region E = 100-1000 V/mm Electrons Side View

  17. Ion Pixel Electron Pixel High Energy Pixel E = 100 V/mm V = 400 V Electrons Ions

  18. Realistic Potential Distribution

  19. Toolchest 4: Finite Difference Electrostatics • We set the electrostatic potential of electrodes/deflectors • Then, in free space, the potential must satisfy Laplace’s equation • Davin Larson wrote code to solve on a grid using a finite difference method

  20. Particle Trajectories in Realistic Potential Distribution

  21. Trajectories: Low Energy Electrons Low Energy Ions Neutrals, High Energy Electrons and Ions Collimators Electrostatic Deflectors Pixelated Detectors (Mounted Back-to-Back) 5 cm Solar Orbiter STE

  22. Energy-Angle Response for Edge Pixels

  23. Energy-Angle Response for Middle Pixels

  24. Center Pixel Response (Electrons) Edge Pixel Response (Electrons) Deflection Voltage Left Sweep Right Sweep 4 kV 1.5 kV 600 0 600 1.5 kV 4 kV • Symmetric response for ions • Neutrals measured in center pixel – cleanly separated for energies below ~15-20 keV • Logarithmic voltage sweep with ten steps from 600V to 4 kV is optimal for • covering phase space. Need positive and negative sweeps to get all angles, • so 20 voltage steps desired.

  25. Telemetry • For edge pixels need 20 voltage steps • To deconvolve, prefer linear energy bins from 2-15 keV (no need to go higher for edge pixels) • Total sweep = 20V*14E*8pixels*8bits = 17920 bits • For center pixels, can sum all voltage steps (not true if you want to do neutrals). • Need 20 logarithmic energy bins to cover 3-100 keV at energy resolution of 0.2 • Total distribution = 20E*8pixels*8bits = 1280 bits • Total instrumental bits per sweep = 19200 • 200bps gives 96sTimeResolution • For CINEMA, Time Tag all Events

  26. Total Instrumental Count Rates at 1 AU (scale up by 25? at 0.2 AU)Shows need for Attenuator for Solar OrbiterSimilar Issue for Auroral Zone for CINEMA Quiet Time Un-Attenuated Quiet Time Attenuated Big SEP Event Un-Attenuated Big SEP Event Attenuated Red = Edge Pixel Black = Middle Pixel

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