Energetic Particles & Boundary Remote Sensing

1. ESS 261 Spring Quarter 2009 Energetic Particles & Boundary Remote Sensing Energetic Particle Instruments: Operation and Data Products Geometric Factor. Contamination: Sunlight, Earth-glow, Neutrals Background/Electronic Noise, Detector Capacitance and Leakage Current. Data Viewing, Removal of Noise and Analysis of Distribution Functions Access, Use and Pitfalls of Analysis in Various Regions:Solar Wind, Magnetosphere, Radiation Belts and Ring Current Remote Sensing of Particle Gradients: Magnetopause, Inner Magnetosphere and Low Frequency Waves Contributions from:”Davin Larson, Thomas Moreau, Andrei Runov and Ryan Caron References: ISSI book on Analysis Methods for Multi-Spacecraft Data Lecture 05 April 27, 2009 Energetic Particles1

2. Interaction of particles with matter [1] • The way in which energetic particles interact with matter depends upon their mass and energy. • Photons - have “infinite range”- Their interaction is “all-or-nothing” They do not slow down but instead “disappear”, typically through one of three interactions (I=I0e-x where  is absorption coefficient ): • Photoelectric effect (Low energy: E<~50 keV • Compton Scattering (50 keV ~< E < 1 MeV) • Pair production ( E >2 x 511 keV). • Particles with non-zero mass (Electrons and Ions) will slow down as they pass through matter. They interact with electrons, phonons and nuclei. • Electron interaction is long-range. Enectron-electron energy exchange peaks when incoming particle is close to the target electron energy. The material electrons have energies that are determined by • The material temperature (phonon-electron interaction couples them) ~kT, ~105m/s • The Fermi energy, i.e., the energy level of free electrons in absolute-zero temperature. This is about 5-10eV, which gives the Fermi speed of 106m/s. Energetic Particles2

3. Pair production Photoelectric effect Compton scattering Energetic Particles3

4. (/ often used: mass attenuation coefficient) Energetic Particles4

5. Interaction of particles with matter [2] • Charged particles primarily interact with the electrons in a material. Typically the energetic particle suffers numerous, distant collisions with a Fermi sea of electrons losing a small amount of energy with each interaction (much like a plasma!). • The interaction is typically strongest when the velocity of the energetic particle is approximately the same as the Fermi speed. • Energetic neutral atoms are quickly ionized soon after entering the solid. • Neutrons are a different matter altogether Energetic Particles5

6. Interaction of particles with matter [3] • The stopping power for heavy particles (ions) is given by the Bethe-Bloch formula (1932): Rate of energy loss is ~ inversely proportional to energy, and proportional to Z (the atomic number) and z2, z the projectile charge I = average ionization potential, D and C = density and shell corrections. Energetic Particles6

7. Interaction of particles with matter [4] • The range is given by: • dE/dx is often expressed in units of keVcm2/gr which is dE/dx times the material density. This bundles the dE/dx curves into groups by normalizing away the material density from the electronic interactions. • The range (typically in cm) is also often normalized to the density and expressed in units of grams/cm2, i.e., the equivalent mass per unit area required to stop the particle. This formula is only useful for ions for reasons we will soon see. Energetic Particles7

8. Interaction of particles with matter [8] • Electrons and Ions behave differently due to the different mass ratio. The primary interaction of all energetic particles is with the sea of electrons. • Ions: • Ions interact with a series of distant collisions. Each interaction results in a small energy loss and very little angular scattering. – They travel in nearly straight lines as they slow down. The dispersion is small. (Imagine a fast bowling ball thrown into a sea of slow moving ping pong balls.) • Electrons: • Electrons can lose a large fraction of their energy and undergo large angle scattering with each interaction (Imagine a high speed ping pong ball thrown into the same sea) Energetic Particles8

9. Interaction of particles with matter [9] • When an electron hits an atom it can undergo a very large angle deflection, often scattering it back out of the material. • Bremstrahlung (braking) radiation is produced when electrons undergo extreme accelerations. X-rays are easily generated when energetic electrons strike high Z materials. (a good reason to avoid high Z materials on exposed surfaces) Energetic Particles9

10. Protons in Energy lost to ionization (collectable) Energy lost to phonons (not collectable) Energetic Particles10

11. Alphas in: Energy lost to ionization (collectable) Energy lost to phonons (not collectable) Energetic Particles11

12. Electrons in Energy lost toionization (collectable) Energy lost toBremstrahlung radiation (notcollectable) Energetic Particles12

13. Solid State Detectors • Solid State Detectors (SSDs) not only detect individual particles, they can be used to measure particle energy with good energy resolution. • Typically only good for E>20 keV • Recent improvements push the limit to ~2 keV • Two varieties of Silicon Diode Detectors • Implanted Ion (i.e. Canberra PIPS) • Produced by implanting p-type material into an n-type silicon substrate • Easy to produce pixelated surfaces • Very rugged • Surface Barrier • Chemical process to create diode surface • Easily damaged, sensitive to solvents • Not too common anymore • Typically both varieties are run fully depleted (electric field extending throughout bulk of material) • Maximum thickness is ~1000 microns – defines max energy particle that can be stopped within the detector • Particles can be incident on either side of detector Energetic Particles13

14. Operation Principle + - • With the application of a (large enough) reverse bias voltage an electric field is established throughout the entire silicon volume (fully depleted detector). • An energetic charged particle will leave an ionization trail in its wake. • The electron hole pairs will separate and drift to opposite sides. • The total charge is proportional to the electronic energy deposited. (3.61 eV per pair for Silicon). • The signal contains only a few thousand electrons thus requiring sensitive electronics. • The trick is to collect and measure this small signal. p - - n + + E Forward bias p - - n + + E particle Reverse bias p - - + + n E Energetic Particles14

15. Detector Electronics Simulated A225response for typical 1MeV electron pulse through a Si detector. The A225 integrates charge, with peak pulse equal to integrated charge. A 20ns signal turns into an 8usec pulse! Energetic Particles15

16. Front End Counting Electronics Energetic Particles16

17. Sources of Noise • Capacitance • Noise results inuncertainty inabsolute valueof energy • Leakage (dark) current • When dark current is integrated by A225 results in baseline offset • Baseline restorer restores zero level • Leakage current results in error in absolute signal amplitude Energetic Particles17

18. Examples of Detector Systems: WIND/3DPPredecessor of THEMIS/SST Energetic Particles18

19. Examples of Detector Systems: WIND/EPACT Cross section of the EPACT isotope telescope on Wind. The first two detectors are two-dimensional position sensitive strip detectors (PSD1, PSD2). They are required so that path-length corrections may be made for the angle of incidence and for non-uniformities in detector thickness. Tungsten rings are used to mask off circular areas for each PSD. There are 6 solid-state detectors increasing in thickness with depth in the stack in order to minimize Landau fluctuations. From von Rosenvinge et al. [1995]. Energetic Particles19

20. Examples of Detector Systems: THEMIS/SST Foil Collimator (for electrons) Attenuator Foil Detector Stack Magnet Attenuator Open Collimator (for ions) Energetic Particles20

21. THEMIS/SST Sensor Unit Schematic Foil Detector Al/Polyamide/Al Foil Thick Detector Open Detector Foil Collimator (electron side) Open Collimator (ion side) Attenuator Attenuator Sm-Co Magnet Energetic Particles21

22. THEMIS/SST Sensor Unit Details • 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 the side measuring electrons) • Filters out ions <~350 keV • Leaves electron flux nearly unchanged • Magnet / Open (on the side measuring ions) • Filters out electrons <400 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 Energetic Particles22

23. Detector Pixelation • Detectors similar to STEREO/STE • Produced at LBNL/Craig Tindall PI Active area 5 mm Guard ring 10 mm Additional Pixels not used for Themis Energetic Particles23

24. Detector Wiring -35 V ~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 Energetic Particles24

25. SST Detector Mechanical Design/Connections • Typical Electrical Connection Between Detector and Flex-Circuit Wirebond Loop (NOT to scale – actual loop height < 300 micron) Kapton Flex-Circuit Detector (pixelated side) Energetic Particles25

26. SST Detector Mechanical 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) Energetic Particles26

27. SST Detector Mechanical: Real Life Energetic Particles27

28. SST Mechanical Design • DFE Board Subassembly Relative Positions • (2 per sensor) Detector Stack Subassembly Foil Frame Multi-Layer Circuit Board (62 mil thickness) AMPTEK Shielding Thermostat Energetic Particles28

29. SST Mechanical Design • Magnet-Yoke Assembly Co-Fe Yoke (2) Sm-Co Magnet (4) (currently not visible) Aluminum Magnet Cage Energetic Particles29

30. SST Mechanical Design • Attenuator Assembly SMA Lever (2) Attenuator (4) Cam (2) Energetic Particles30

31. SST Mechanical Design • Actuators and Position Switches Honeywell SPDT Hermetically Sealed Switch (2) SMA Actuator (2) Energetic Particles31

32. SST Mechanical Design • Two Collimators Per Side Ion Side Electron Side Energetic Particles32

33. SST Mechanical Design • Four Collimators Per Sensor Ion Side Electron Side Electron Side Ion Side Energetic Particles33

34. SST Mechanical Design • Support Structure • (back section) Rigid Mounting Flange Electrical Connector Bottom Closeout Panel Energetic Particles34

35. SST Mechanical Design • Support Structure • (front section) Rigid Mounting Flange Kinematic Flexure (2) Energetic Particles35

36. SST Mechanical Design • Bi-Directional Fields-of-View Energetic Particles36

37. SST Mechanical Design • Sensor Orientation Relative to Spacecraft Bus Energetic Particles37

38. SST Mechanical Design • Sensor Unit Mounting Using Kinematic Flexures • Each sensor mounted to spacecraft panel at three points • One rigid mounting flange • Two mounting flanges with kinematic flexures • Allows relative motion due to CTE differences between sensor structure and spacecraft panel • Predicted expansion differential along instrument axes with 120 ºC temperature gradient: • X-Axis: 0.006” (0.15 mm) • Y-Axis: 0.013” (0.33 mm) • Flexure dimensions sized to keep maximum bending stresses below 6061-T6 yield strength • Factor of Safety (F.S.) > 1.4 per NASA-STD-5001 Energetic Particles38

39. SST Mechanical Design • Attenuator Actuation – CLOSED position Honeywell Switch (compressed-position) Honeywell Switch (extended-position) SMA Actuator (retracted) SMA Actuator (extended) Energetic Particles39

40. SST Mechanical Design • Attenuator Actuation – OPEN position Honeywell Switch (extended-position) Honeywell Switch (compressed-position) SMA Actuator (extended) SMA Actuator (retracted) Energetic Particles40

41. Linear Actuators • Shaped Memory Alloy (SMA) actuator • Single direction 125 gram pull-force • Required force < 42 gram => F.S. > 3.0 • Operating temp range: -70°C to +75°C Extended Position Retracted Position Relative Size (commercial model shown) Energetic Particles41

42. Magnetics Testing • Magnet Cage assembly #1 • Measured Py for 19 magnets (All values were very close) • Selected 4 magnets for assembly #1 • Measured dipole and quadrapole moments of assembly • Found significant residual dipole moment along x-axis • Contribution of dipole and quadrapole nearly equal at 2 m • Conclusion: Px and Pz of individual magnets are important Energetic Particles42

43. Magnetics Testing • Sent Magnet Cage assembly #2 to UCLA for testing • Results are virtually the same • Contribution of dipole and quadrapole fields are similar at 2 m: • B(dipole @ 2m) = .88 nT • B(quad @ 2m) = .59 nT • The sum of both contributions exceeds requirement (0.75 nT @ 2m) • Relaxed requirement, since it is a DC field Energetic Particles43

44. Electronics Block Diagram • Signal chain: 1 of 12 channels shown Bias Voltage Test Pulser DAC Thresh Gain FPGA Coincidence Logic & Accumulators PD A225F Preamp Shaper ADC Memory BLR DFE Board DAP Board Energetic Particles44

45. FPGA Functions: Interface to ETC • Using Actel RT54SX72S (modeled on STEREO/STE) • Controls 12 ADCs • Monitor / Count threshold events • Monitor peak detect signal • Produce convert strobe • Coincidence detection • Readout ADC (energy) • Psuedo-logrithmic energy binning • ADC measurement used as address of LUT to increment accumulators (LUTs and accumulators stored in SRAM) • Data Readout (controlled by ETC board) • Command Data Interface (CDI) (loads tables) • Test Pulser control • Noise measurement • Periodic conversions to measure “noise” • Analog Housekeeping control Energetic Particles45

46. SST Products • Products: Full, Reduced (Burst is same as full) • Full: 16E x 64A • Reduced: 16E x 6A , or 16E x 1A (omni) • Modes: Slow Survey, Fast Survey, Particle Burst • Slow Survey: • Full distributions (ions and electrons) at 5min resolution • Reduced, omnidirectional distributions: every spin • Fast Survey: • Ions: Full distributions every spin • Electrons: Reduced distributions (16E x 6A) every spin • Burst: • Ions: same as above • Electrons: Full distributions every spin Energetic Particles46

47. SST Accommodation SSTs Energetic Particles47 Angelopoulos, 2008

48. SST Accommodation Energetic Particles48 Angelopoulos, 2008

49. Data Analysis Tools [1] • Pitfalls • Sun contamination • ; Sun contamination is masked on board but often fails; Use keyword: mask_remove to removed masked bins and interpolate across sectors • ; Sun contamination is lefted unmasked recently (and most of the time) on board ; There is code to recognize the faulty bins (saturated) and remove them altogether.; This is called : method_sunpulse_clean='spin_fit' , or ‘median’ and tells the; programs to remove data beyond 2sigma away from spin-phase fit/median. • ;Sun contamination/saturation also affects other channels due to electronic noise.;The code can remove the typical noise value and provide the remaining good; signal (assuming no saturation). The keyword is: enoise_bins and the; procedure is documented in: thm_crib_sst_contamination.pro Energetic Particles49

50. Sun contamination (thm_crib_sst_contamination.pro) • ;PROCEDURE: thm_crib_sst_contamination • ;Purpose: 1. Demonstrate the basic procedure for removal of sun contamination, • ; electronic noise, and masking. • ; 2.. Demonstrate removal of suncontamination via various methods. • ; 3. Demonstrate the correction of inadvertant masking in SST data • ; 4. Demonstrate scaling data for loss of solid angle in SST measurements. • ; 5. Demonstrate substraction of electronic noise by selecting bins in a specific region • ; 6. Show how to use these techniques for both angular spectrograms,energy spectrgrams, and moments. • ;SEE ALSO: • ; thm_sst_remove_sunpulse.pro(this routine has the majority of the documentation) • ; thm_part_moments.pro, thm_part_moments2.pro, thm_part_getspec.pro • ; thm_part_dist.pro, thm_sst_psif.pro, thm_sst_psef.pro,thm_sst_erange_bin_val.pro • ; thm_crib_part_getspec.pro Sun contamination (sst_remove_sunpulse.pro) • ; Routine to perform a variety of calibrations on full distribution sst data. These can remove sun contamination and on-board masking. They can also scale the data to account for the loss of solid angle from the inability of the sst to measure directly along the probe geometric Z axis and the inability to measure directly along the probe geometric xy plane.(ie X=0,Y=0,Z = n or X=n,Y=m,Z=0, are SST 'blind spots') THM_REMOVE_SUNPULSE routine should not generally be called directly. Keywords to it will be passed down from higher level routines such as, thm_part_moments, thm_part_moments2, thm_part_dist,thm_part_getspec, thm_sst_psif, and thm_sst_psef Energetic Particles50