THEMIS Electric Field Instrument (EFI) Dr. John Bonnell Space Sciences Laboratory UC Berkeley

1. THEMIS • Electric Field Instrument (EFI) • Dr. John Bonnell • Space Sciences Laboratory • UC Berkeley

2. Performance vs. Specifications • EFI has met or exceeded on-orbit performance requirements and specifications (all requirements and specs included in appendix): • 30 sensors still functional and in spec after 33 months on-orbit, including long- and short-duration eclipses (lifetime; thermal). • No obvious signs of degradation in performance: • no dramatic increases in offsets or shifts in gain. • no increases in power consumption. • no loss of current- or voltage-bias control. • no problems with commanding or configuration control. • 2D DC and 3D AC E-field estimates from EFI have been made in support of all three mission objectives: • Substorm Onset (E-fields in tail to 1 mV/m) • Radiation Belt Acceleration Processes (AC measurements to 4-8 kHz. • Dayside Magnetopause Observations (E fields at M’Pause to few mV/m). • On-orbit calibration and offset estimation and removal allow for accuracies better than 1 mV/m, if cold plasma wake effects are not present.

3. Assessment of Data Products (1) • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-1 to -4):

4. Assessment of Data Products (2) • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-5 to -10):

5. Assessment of Data Products (3) • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-11 to -13):

6. Assessment of Data Products (2) • L1 EFI data products support investigations beyond L1 science requirements: • Hall E-field measurements at the dayside magnetopause (e.g. Mozer et al., 2008). • Hall E-field measurements in tail dipolarization events (McFadden, private comm., 2008-9). • Coordinated E- and B-field measurements in geomagnetic pulsation studies (spin-fit and waveform) (e.g. Liu et al., 2009). • Double layer and electron hole observations in magnetotail (e.g. Andersson et al., 2009; Ergun et al., 2009).

7. Data Maturity (1) • L1 EFI data reprocessed several times in order to remove on-board data collection anomalies: • Time Tagging, prior to correction in FSW. • Spikes in high-rate (WaveBurst) data (impacts << 0.1% of WB data). • L1 data is accessible through TDAS package (IDL crib sheets and procs), as well as the Science Data Tool (old-school E-field community). • Calibration has both fixed (gains, sunward offsets) and time-dependent elements. • Fixed calibration parameters (gains sunward/dawn-dusk offsets) computed using cal runs in magnetosheath. • Time-dependent element is computed on-the-fly in TDAS and SDT processing, both for DC (FastSurvey) and AC (Pburst, Wburst) data types. • Accuracy is at least 1 mV/m for 2D spin plane fields, with few tens of mV/m for the axial estimate (after heavy processing). • Description and discussion of calibration and error sources in Bonnell et al. (2008), as well as on EFI Instrument web page.

8. Data Maturity (2) • Preliminary quality flags available, but not formalized: • detection of wake effect fields through comparison of long- and short-antenna results. • Limitation of E∙B=0 estimates of Eperp to limited ranges of (Bspin/Baxial). • L2 EFI data processing in the works, but data still needs significant care in use and interpretation.

9. EFI Lessons Learned • Wake effect fields due to flowing cold plasma have significant impact (tens of mV/m) on magnetospheric side of dayside magnetopause, as well as in inner magnetosphere → • longer booms. • SC potential control. • continuous waveform measurements, or spin-fit of both spin plane signals, rather than just one. • 7-m tip-to-tip axial antennas are too short for making 1 mV/m 3D DC measurements → • longer booms. • adjustable boom lengths on-orbit. • Photoelectron fluxes returning to SC and body-mounted particle detectors can be significant and can impact low-energy (few to tens eV) e- measurements → • GUARD surfaces run at positive, rather than negative potentials. • adjust voltage biasing scheme of DBRAID surfaces during sensor eclipse season.

10. BACKUP SLIDES: • References. • Requirements and Specs. • On-Orbit Operation and Calibration. • Measurement Challenges.

11. References • Andersson et al., New features of electron phase space holes observed by the THEMIS mission, PRL, accepted, 30 Apr 2009. • Bonnell et al., The electric field instrument (EFI) for THEMIS, SSR, doi:10.1007/s11214-008-9469-2. • Bortnik et al., An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions, Science 324, 5928, 775 - 778, doi: 10.1126/science.1171273. • Cully et al., THEMIS Observations of Long-lived Regions of Large-Amplitude Whistler Waves in the Inner Magnetosphere, GRL, doi:10.1029/2008GL033643. • Ergun et al., Observations of Double Layers in Earth’s Plasma Sheet , PRL, 102, 155002. • Li et al., Global Distribution of Whistler-mode Chorus Waves Observed on the THEMIS Spacecraft, GRL, 2009. • Liu et al, Solar wind influence on Pc4 and Pc5 ULF wave activity in the inner magnetosphere, GRL, accepted, 2009. • Mozer et al., THEMIS observations of modified Hall fields in asymmetric magnetic field reconnection, GRL, doi:10.1029/2007GL033033. • Segeev et al., THEMIS observations in the near-tail portion of the inner and outer plasma sheet flux tubes at substorm onset, JGR, doi:10.1029/2008JA013527. • Sergeev et al., Kinetic structure of the sharp injection/dipolarization front • in the flow-braking region, GRL,doi:10.1029/2009GL040658.

12. Lifetime, Radiation

13. Mass, Power, Thermal

14. Cleanliness; Elect., Mech. ICD

15. Environmental Testing

16. Science Requirements

17. Performance Requirements

18. Performance Requirements

19. EFI Board Requirements

20. EFI Board Requirements

21. EFI Boom Requirements

22. ON-ORBIT OPERATION AND CALIBRATION

23. On-Orbit Current and Voltage Bias Sweeps “Sensor Diagnostic Test (SDT)”

24. E vs. –VxB (EFI/FGM/ESA Inter-Calibration)

25. E vs. –VxB (EFI/FGM/ESA Inter-Calibration)

26. E vs. –VxB (EFI/FGM/ESA Inter-Calibration)

27. Vsc vs. Ambient Density • Typical two-slope correlation between Vsc and ambient ion density estimate (iESA).

28. MEASUREMENT CHALLENGES

29. ES Cold Plasma Wake • Waveforms non-sinusoidal and significant amplitude (tens of mV/m). • Shorter boom pair (E34) has LARGER signal than long boom pair (E12). • Occurrance consistent with ESA cold plasma observations, when available: • ne>ni • cold (few eV) flowing ions present in iESA spectrum • Distortion reminiscent of cold plasma wake effect on Cluster [eg. Engwall et al., 2006]. • Rate of occurrence on THEMIS is high; initial estimates of 60-80% of duskside passes. • Significant for MMS, RBSP E-field measurements. • PIC simulation by Engwall & Eriksson (CLUSTER booms)

30. Short Booms: Axial E vs. Vsc • Significant correlation between v56 (axial E-field) and Vsc over a broad range of spacecraft potentials (ambient densities) – ≈ 4 ((mV/m)/V) • Correlation is not strictly linear, and breakpoints probably represent changes in photocloud structure with SC potential. • Partly explained by the shift in the electrostatic center caused by the mag booms (≈ 6 cm shift!).

31. What’s Calibration Error and What’s E||?