ESA In-Flight Calibration and First Results

1. ESA In-Flight Calibration and First Results J. McFadden, C. Carlson, D. Larson UC Berkeley SSL

2. Requirements and Specifications • The ESA instrument measures 3-D electron and ion energy distribution functions over the Energy range ~5 eV to 30 keV (25 keV for ions). • Typical energy sweep has 16 or 32 energy samples and logrithmic sweep (dE/E~constant). • A full 4-pi distribution measurement is produced during each spin. • Sweep rate of 32/spin gives dense sample of 3-D particle distributions. Ion sensor is capable of 64 sweeps/spin to provide adequate sampling of solar wind. • The ETC board compresses the raw measurements into three selectable “distributions arrays” that come down in separate packets (full, burst and reduced packets) at selectable rates. • The ETC also computes moments with corrections for detector efficiency and spacecraft potential.

3. Block Diagram • Electronics functional design is identical to FAST (with ACTEL upgrades) • Three circuit modules plug together for efficient assembly and test • MCP pulse amplifiers are Amptek A121 with programmable gain • All discrete logic, counters, and HV DAC drivers are Actel FPGAs • HV & LV supplies are mature designs built at UCB SSL

4. ESA S/C INTERFACE Ion and Electron ESAs are packaged together. 180 deg x 6 deg field of view Sensors have different anode patterns. Ion ESA Electron ESA 16 Anodes 8 Anodes

5. ESA Data Types THEMIS produces four basic ESA data products for each species with resolution that depends upon instrument mode: Full distributions – Low cadence (~32 or 128 spin resolution), high resolution energy-angle (32E x 88A) distributions, taken continuously over the orbit. Burst distributions – High cadence (every spin), high resolution energy-angle (32E x 88A) triggered snapshots (~4 minutes). Reduced distributions – High cadence (every spin), lower resolution (32E x 1A i+&e-, 32E x 6A e-, or 24E x 50A i+) distributions taken continuously over the orbit. Onboard Moments – High cadence (every spin) density, velocity, pressure, heat flux.

6. ESA Data Types Typical 88 solid-angle map used for sorting full and burst data

7. ESA Data Analysis Software 1 Data structure at right is loaded into IDL memory by the below routines. thm_load_esa_pkt.pro – creates 6 IDL ESA data structures containing time, counts, energy & angle arrays, geometric factors, etc. thm_load_esa_pot.pro – adds the spacecraft potential to the ESA data structures. thm_load_esa_mag.pro – adds the magnetic field to the ESA data structures. PROJECT_NAME STRING 'THEMIS' SPACECRAFT STRING 'c' DATA_NAME STRING 'IESA 3D Reduced' APID INT 455 UNITS_NAME STRING 'compressed' UNITS_PROCEDURE STRING 'thm_convert_esa_units' VALID BYTE Array[27909] TIME DOUBLE Array[27909] END_TIME DOUBLE Array[27909] DELTA_T DOUBLE Array[27909] INTEG_T DOUBLE Array[27909] DT_ARR FLOAT Array[32, 88, 8] CS_PTR LONG Array[27909] CS_IND INT Array[27909] CONFIG1 BYTE Array[27909] CONFIG2 BYTE Array[27909] AN_IND INT Array[27909] EN_IND INT Array[27909] MD_IND INT Array[27909] NENERGY INT Array[6] ENERGY FLOAT Array[32, 6] DENERGY FLOAT Array[32, 6] EFF FLOAT Array[32, 6] NBINS INT Array[8] THETA FLOAT Array[32, 88, 8] DTHETA FLOAT Array[32, 88, 8] PHI FLOAT Array[32, 88, 8] DPHI FLOAT Array[32, 88, 8] PHI_OFFSET FLOAT Array[27909] DOMEGA FLOAT Array[32, 88, 8] GF FLOAT Array[32, 88, 8] GEOM_FACTOR FLOAT 0.00110000 DEAD FLOAT 1.60000e-007 MASS FLOAT 0.0104389 CHARGE FLOAT 1.00000 SC_POT FLOAT Array[27909] B_GSE FLOAT Array[27909, 3] MAGF FLOAT Array[27909, 3] DAT0 BYTE Array[6, 16] DAT1 BYTE Array[13753, 32] DAT2 BYTE Array[1, 96] DAT3 BYTE Array[1, 192] DAT4 BYTE Array[1, 1152] DAT5 BYTE Array[14150, 1200]

8. ESA Data Analysis Software 2 Commands to load & plot ESA data: startdate = '2007-07-31/0:00' sc='b' ndays=1 thm_init timespan,startdate,ndays thm_load_state,probe=sc thm_load_esa_pkt,probe=sc thm_load_esa_mag,sc=sc thm_load_esa_pot,sc=sc tplot,[‘thb_pe??_en_counts’] Default plots are in “counts”. Note discontinuity in ion 24 energy mode. Calibrated data in energy flux do not have this discontinuity.

9. ESA Data Analysis Software 2 Once the data are loaded, use these routines to return an ESA data structure at a single time. get_thc_peir.pro p – particle (f – fields) e – ESA (s – SST) i – ion (e - electron) r – reduced (f-full,b-burst) Routines that operate on structures n_3d_new.pro v_3d_new.pro Loop routines for time series plots get_2dt.pro get_en_spec.pro Example IDL commands t=‘2007-5-5/12:31’ dat=get_thc_peir(t) dat=get_thc_peir() dat=get_thc_peir(/ad) dat=get_thc_peir(/re) print,n_3d_new(dat) print,n_3d_new(dat,energy=[0,20]) get_2dt,’n_3d_new’,’thc_peir’ get_en_spec,’thc_peir’,name=‘test’

10. ESA Plot Types and Units 1 Once the data are loaded, there are several plotting routines. dat=get_thb_peif() spec3d,dat spec3d,dat,units=‘df’ Each angle bin is a different color curve. For 3-D angle maps use: plot3d,dat

11. ESA Plot Types and Units 2 Plot3d acting on data structure “dat” produces the below plot. Example IDL command: plot3d,dat,/zero Magnetic field indicated by plus and diamond

12. ESA Plot Types and Units 3 IDL routines for time series plots get_en_spec get_2dt

13. ESA In-Flight Calibration • ESA in-flight calibration and instrument maintenance requires: • Getting the timing straightened out - finished • MCP Bias Voltage determination - ongoing • Sunlight contamination - minimal • Spacecraft potential correction - in place • Dead-time corrections - in place • Energy efficiency corrections - in progress • Relative efficiency corrections - TBD • Absolute efficiency - TBD • Electron-Ion cross calibration - TBD • Inter-spacecraft cross calibrations - TBD

14. ESA MCP detector tests A121 preamps allow simple determination of MCP bias voltage requirements. Toggling the gain should change efficiency by factor of ~ 2-3 for proper MCP bias voltage. Electron sensor (panel 3&4) above showed efficiency changes of ~4 so MCP bias voltage was raised 50V. The gain test repeated to the right confirms proper operation. Bias voltage changes (not shown) are also toggled to expose any significant losses near threshold.

15. Sunlight & Photo-electrons No measureable direct sunlight contamination. Spacecraft photo-electrons must be eliminated. Photo-electrons are produced in the aperture, on the spacecraft and on langmuir probes. sc_pot=20V Wire boom photo-e s/c photo-e Axial boom photo-e Wire boom photo-e sc_pot=45V sc_pot=11V

16. Correcting for s/c potential Thm_load_esa_pot.pro Software currently assumes s/c potential is 1.15 times the measured average spin plane boom potential (V1234) plus 1 volt contact potential. 1.15 calibration factor determined from density comparisons. Similar to simulations conducted by Cully. s/c potential corrections are important for electrons and cold ions.

17. Correcting for dead time Total dead-time is a combination of “preamplifier dead-time” and “detector dead-time”, which is difficult to calibrate and depends on MCP bias voltage and preamplifier threshold. For the above case, high density results in significant electron ESA deadtime. This allowed an estimate of total deadtime (~0.16 us) by eliminating the slope in the Ni/Ne density ratio (right, bottom panel).

18. Detector Energy Efficiency 1 For log energy and 2 kV pre-acceleration, the efficiency is shown below. Default ion efficiency assumes lab results from Funsten. Energy (eV)

19. Detector Energy Efficiency 2 Electron efficiency assumes: “Relative electron detection efficiency of microchannel plates from 0-3 keV”, R.R. Goruganthu and W. G. Wilson, Rev. Sci. Instrum. Vol. 55, No. 12 Dec 1984. Efficiency formula: (1-exp(-k*delta/delta_max))/(1-exp(-k))

20. Detector Energy Efficiency 3 Ion efficiency corrected – work in progress: Default ion efficiency produces a slope in the Ni/Ne ratio (right bottom). Default Energy (eV) Proposed ion efficiency eliminates this slope. Difference assumed to be due to fringing fields at the detector. Proposed Energy (eV)

21. Detector Energy Efficiency 4 Electron efficiency: The proposed electron energy efficiency curve seems to produce more consistent electron-ion density ratios over a number of orbits. More investigation is needed, but difference appears to be due to secondary e- production in ESA. Current e- efficiency Proposed e- efficiency Energy (eV) Energy (eV)

22. ESA N,V Cross Calibration Electron-Ion density ratios should agree at the ~5% level. Ne should be less than Ni since Ni is calculated assuming H+. Variations in calculated electron velocity are due to small density fluctuations during a s/c spin.

23. TBD Cross Calibrations Relative Anode Calibrations. Absolute Sensitivity Calibrations. Pressure Balance Tests. Corrections for Composition. Cross Calibrations between spacecraft. Cross Calibrations with SSTs. -VxB vs E Cross Calibrations

24. ESA Data Problems Early data had some table loading problems where counts were incorrectly mapped or ETC would freeze. Table loading bugs fixed ~April 27 and table freeze problem solved ~June 1.

25. ESA Data Problems We occasionally still find bugs in the software, so if something looks wrong – it may be wrong . The below problem is under investigation.

26. EFI induced s/c charging

27. Cold Ions at Magnetopause 4 of 5 s/c observing cold ions at MP Cold ion densities generally 1-2/cc, but can be in the 10-20/cc range (13 cases out of ~90) Hot ion densities are ~0.1-0.3/cc. tha thb thc thd the

28. Cold Ions at Magnetopause Note the lack of cold ions except just inside the MP.

29. First Results – Cold Plasma Cold ions become visible when the MP moves. At times the He+ is observed with density about 1% of the H+ density. To determine whether cold ions are plasmaspheric or conic outflow, check if velocity is along B or perpendicular to B.

30. First Results – Cold Plasma Cold ions become visible when the MP moves with 3 min oscillations

31. Cold ions or conics? Differences between electron and ion densities are often due to missed cold ions, but can also be due to ions with higher mass. Conics often appear with a broader energy, are generally field aligned, and tend to be oxygen.