THEMIS Electric Field Instrument EFI Dr John Bonnell

THEMIS Electric Field Instrument (EFI) Dr. John Bonnell Space Sciences Laboratory UC Berkeley THEMIS EOMP Review EFI Nov 19, 2009

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. • 2 D DC and 3 D AC E-field estimates from EFI have been made in support of all three mission objectives: • Substorm Onset (E-fields in tail to 1 m. V/m) • Radiation Belt Acceleration Processes (AC measurements to 4 -8 k. Hz. • Dayside Magnetopause Observations (E fields at M’Pause to few m. V/m). • On-orbit calibration and offset estimation and removal allow for accuracies better than 1 m. V/m, if cold plasma wake effects are not present. THEMIS EOMP Review EFI Nov 19, 2009

Assessment of Data Products (1) • L 1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-1 to -4): REQUIREMENT EFI DESIGN IN. EFI-1. The EFI shall determine the 2 D spin plane electric field at the times of onset at 8 -10 Re. Compliance. Via compliance with IN. EFI-5 and -13. Both spin-fit (3 -s resolution) and waveform (4 -, 128 -, 4096/8192 -samp/s provided); e. g. Sergeev et al. , 2008; Uritsky et al. , GRL, 2009). IN. EFI-2. The EFI shall determine the dawn/dusk electric field at 18 -30 Re. Compliance. Via compliance with IN. EFI-5 and -13. Measures both components well. (e. g. Sergeev et al. , 2008). IN. EFI-3. The EFI shall measure the 3 D wave electric field in the frequency range 1 -600 Hz at the times of onset at 8 -10 Re. Compliance. Via compliance with IN. EFI-6, -8, -9, -10, and – 11. (e g. Sergeev et al. , 2009). Low-frequency end (<10 Hz) requires significant processing on axial measurements. IN. EFI-4. The EFI shall measure the waves at frequencies up to the electron cyclotron frequency that may be responsible for electron acceleration in the radiation belt. Compliance. Via compliance with IN. EFI-6, -8, -9, -10, and – 11. (e g. Bortnik et al. , 2009; Li et al. , 2009) Both waveform and spectral data supplied; wake effects can contaminate results in some cases. THEMIS EOMP Review EFI Nov 19, 2009

Assessment of Data Products (2) • L 1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-5 to -10): REQUIREMENT EFI DESIGN IN. EFI-5. The EFI shall measure the 2 D spin plane DC E-field with a time resolution of 10 seconds. Compliance. On-board spin-fit of spin plane E-field at 3 -s (one-spin) resolution. (e. g. Liu et al, GRL, accepted, 2009). IN. EFI-6. The EFI shall measure the 3 D AC E-field from 1 Hz to 4 k. Hz. Compliance. 3 -axis E-field measurement sampled at 8 ksamp/s. See AC Error Budget. Verified through Calibration. (e. g. Cully et al. , GRL, 2008; Ergun et al. , 2009) IN. EFI-7. The EFI shall measure the Spacecraft Potential with a time resolution better than the spin rate (3 seconds; from ESA to compute moments). Compliance. On-board spin-avg’d sphere potentials at 3 -s (spin-rate) resolution; EFI data rate allocation includes single spheres at ¼-rate of E-field data. IN. EFI-8. The EFI DFT Spectra Range shall be 16 Hz to 4 k. Hz, with df/f~25%. Compliance. Spectral products from DFB cover 8 Hz to 8 k. Hz at 5%, 10%, or 20% BW (16, 32, or 64 bins). Verified at DFB Functional Test. (e. g. Bortnik et al. , Nature, 2009). IN. EFI-9. The EFI shall measure DC-coupled signals of amplitude up to 300 m. V/m with 16 -bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified at DFB Functional Test. (e. g. Cully et al. , GRL, 2008). IN. EFI-10. The EFI shall measure AC-coupled signals of amplitude up to 50 m. V/m with 16 -bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified at DFB Functional Test. (e. g. Andersson et al. , PRL, 2009). THEMIS EOMP Review EFI Nov 19, 2009

Assessment of Data Products (3) • L 1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-11 to -13): REQUIREMENT EFI DESIGN IN. EFI-11. The EFI noise level shall be below 10 -4 (m. V/m)/Hz 1/2. Compliance. Low-noise preamp chosen (OP-15); good analog design practices throughout preamp, BEB and DFB; CBE in Flight config is few times 10 -4 (m. V/m)/Hz 1/2. (e. g. Cully et al. , GRL, 2008). IN. EFI-12. The EFI HF RMS (Log power) measurement shall cover 100 -500 k. Hz with a minimum time resolution of the spin rate (on-board triggers). Compliance. Measured end-to-end gain of EFI sensors in the 100 -500 -k. Hz band is 0. 4; DFB provides HF-RMS at 1/16 to 8 samp/s. Verified at DFB Functional Test and Sci. Cal. Trigger functions written to use HF_RMS signal, and study of use of HF_RMS as indicator of plasma wave activity performed (Cully, private comm. , 14 May 2008). IN. EFI-13. The EFI shall achieve an accuracy better than 10% or 1 m. V/m in the SC XY E-field components during times of onset. Compliance. See DC Error Budget Discussion. (e. g. Sergeev et al, JGR, 2008). THEMIS EOMP Review EFI Nov 19, 2009

Assessment of Data Products (2) • L 1 EFI data products support investigations beyond L 1 science requirements: • Hall E-field measurements at the dayside magnetopause (e. g. Mozer et al. , 2008). • Hall E-field measurements in tail dipolarization events (Mc. Fadden, 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). THEMIS EOMP Review EFI Nov 19, 2009

Data Maturity (1) • L 1 EFI data reprocessed several times in order to remove on-board data collection anomalies: • • L 1 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 timedependent elements. • • Time Tagging, prior to correction in FSW. Spikes in high-rate (Wave. Burst) data (impacts << 0. 1% of WB data). 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 (Fast. Survey) and AC (Pburst, Wburst) data types. Accuracy is at least 1 m. V/m for 2 D spin plane fields, with few tens of m. V/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. THEMIS EOMP Review EFI Nov 19, 2009

Data Maturity (2) • Preliminary quality flags available, but not formalized: • • • detection of wake effect fields through comparison of long- and shortantenna results. Limitation of E∙B=0 estimates of Eperp to limited ranges of (Bspin/Baxial). L 2 EFI data processing in the works, but data still needs significant care in use and interpretation. THEMIS EOMP Review EFI Nov 19, 2009

EFI Lessons Learned • Wake effect fields due to flowing cold plasma have significant impact (tens of m. V/m) on magnetospheric side of dayside magnetopause, as well as in inner magnetosphere → • • 7 -m tip-to-tip axial antennas are too short for making 1 m. V/m 3 D DC measurements → • • • longer booms. SC potential control. continuous waveform measurements, or spin-fit of both spin plane signals, rather than just one. 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 e. V) e- measurements → • • GUARD surfaces run at positive, rather than negative potentials. adjust voltage biasing scheme of DBRAID surfaces during sensor eclipse season. THEMIS EOMP Review EFI Nov 19, 2009

BACKUP SLIDES: • References. • Requirements and Specs. • On-Orbit Operation and Calibration. • Measurement Challenges. THEMIS EOMP Review EFI Nov 19, 2009

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/s 11214 -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. 1029/2008 GL 033643. • 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 Pc 4 and Pc 5 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. 1029/2007 GL 033033. • 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. 1029/2008 JA 013527. Sergeev et al. , Kinetic structure of the sharp injection/dipolarization front in the flow-braking region, GRL, doi: 10. 1029/2009 GL 040658. THEMIS EOMP Review EFI Nov 19, 2009

Lifetime, Radiation REQUIREMENT EFI DESIGN IN-1. The Instrument Payload shall be designed for at least a two-year lifetime. Compliance. Lifetime has been considered in all aspects of EFI and DFB design (parts, performance degradation, etc. ). IN-2. The Instrument Payload shall be designed for a total dose environment of 33 krad/year (66 krad for 2 year mission, 5 mm of Al, RDM 2) Compliance. Common Parts Buy for Instrument Payload. All parts screened for total dose. Radiation testing planned if TID is unknown. IN-3. The Instrument Payload shall be Single Event Effect (SEE) tolerant and immune to destructive latchup. Compliance. Common Parts Buy for Instrument Payload. All parts screened for total dose. Radiation testing planned if LET is unknown. THEMIS EOMP Review EFI Nov 19, 2009

Mass, Power, Thermal REQUIREMENT EFI DESIGN IN-7. No component of the Instrument Payload shall exceed the allocated mass budget in THM-SYS-008 THEMIS System Mass Budget. xls Compliance. SPB: 1. 816 kg Allocated; 1. 80 kg (F 1 measured). AXB: 4. 185 kg Allocated; 4. 103 kg (F 1 measured). BEB: 0. 464 kg Allocated; 0. 462 kg (F 1 measured). DFB: 0. 398 kg Allocated; 0. 400 kg (F 1 measured) Harness: 0. 905 kg Allocated; 0. 905 kg (F 1 measured) IN-9. No component of the Instrument Payload shall exceed the power allocated in THM-SYS-009 THEMIS System Power Budget. xls Compliance. Preamps: 0. 09 W Allocated; 0. 05 W (FLT nominal). note: Preamp power included in BEB allocation. BEB: 1. 76 W Allocated; 1. 1 W CBE (ETU). DFB: 0. 853 W/0. 890 W/1. 470 W max. IN-13. The Instrument Payload shall survive the temperature ranges provided in the ICDs. Compliance. SPB and AXB received 4 cycles at Instrument level, with Hot and Cold deploy tests. Preamp Thermal Qual (ETU) and Acceptance (FLT) tests completed prior to Instrument integration. IN-14. The Instrument Payload shall perform as designed within the temperature ranges provided in the ICDs Compliance. See IN-13. THEMIS EOMP Review EFI Nov 19, 2009

Cleanliness; Elect. , Mech. ICD REQUIREMENT EFI DESIGN IN-16 The Instrument Payload shall comply with the Magnetics Cleanliness standard described in the THEMIS Magnetics Control Plan Compliance. THM-SYS-002 Magnetics Control Plan. Budget for EFI Magnets (Boom Motors) is <0. 75 n. T @ 2 meters; CBE by measurement is 0. 25 n. T @ 2 meters. IN-17 The Instrument Payload shall comply with the THEMIS Electrostatic Cleanliness Plan Compliance. Design, fabrication, and testing in accordance with THM-SYS-003 Electrostatic Cleanliness Plan. Verified at Instrument level in CPT/LPT testing. IN-18 The Instrument Payload shall comply with the THEMIS Contamination Control Plan Compliance. Design and fabrication in accordance with THM-SYS-004 Contamination Control Plan. IN-19. All Instruments shall comply with all electrical specifications Compliance. Design in accordance with THM-IDPU 001 Backplane Specification (BEB, DFB). Verified by board-level and IDPU-integration level testing. IN-20. The Instrument Payload shall be compatible per IDPU-Instrument ICDs Compliance. THM-SYS-103 DFB-to-IDPU ICD signed off. THM-SYS-104 BEB-to-IDPU ICD signed off. ICD compliance confirmed by direct measurement during II&T. IN-21. The Instrument Payload shall be compatible per the IDPU-Probe Bus ICD. Compliance. Both THM-SYS-108 Probe-to-EFI Radial Booms ICD, and THM-SYS-109 Probe-to-EFI Axial Booms ICD are signed off. ICD compliance confirmed by direct measurement during II&T. THEMIS EOMP Review EFI Nov 19, 2009

Environmental Testing REQUIREMENT EFI DESIGN IN-23 The Instrument Payload shall verify performance requirements are met per the THEMIS Verification Plan and Environmental Test Spec. Compliance. Instrument Suite-level environmental testing to be completed as per THM-SYS-005 Verification Plan and Environmental Test Specification. IN-24 The Instrument Payload shall survive and function prior, during and after exposure to the environments described in the THEMIS Verification Plan and Environmental Test Specification. Compliance. Instrument Suite-level environmental testing to be completed as per THM-SYS-005 Verification Plan and Environmental Test Specification. Suite-level CPT developed during II&T of F 1. THEMIS EOMP Review EFI Nov 19, 2009

Science Requirements REQUIREMENT EFI DESIGN IN. EFI-1. The EFI shall determine the 2 D spin plane electric field at the times of onset at 8 -10 Re. Compliance. Via compliance with IN. EFI-5 and -13. IN. EFI-2. The EFI shall determine the dawn/dusk electric field at 18 -30 Re. Compliance. Via compliance with IN. EFI-5 and -13. IN. EFI-3. The EFI shall measure the 3 D wave electric field in the frequency range 1 -600 Hz at the times of onset at 8 -10 Re. Compliance. Via compliance with IN. EFI-6, -8, -9, -10, and – 11. IN. EFI-4. The EFI shall measure the waves at frequencies up to the electron cyclotron frequency that may be responsible for electron acceleration in the radiation belt. Compliance. Via compliance with IN. EFI-6, -8, -9, -10, and – 11. THEMIS EOMP Review EFI Nov 19, 2009

Performance Requirements REQUIREMENT EFI DESIGN IN. EFI-5. The EFI shall measure the 2 D spin plane DC E-field with a time resolution of 10 seconds. Compliance. On-board spin-fit of spin plane E-field at 3 -s (one-spin) resolution. IN. EFI-6. The EFI shall measure the 3 D AC E-field from 1 Hz to 4 k. Hz. Compliance. 3 -axis E-field measurement sampled at 8 ksamp/s. See AC Error Budget. Verified through Calibration. IN. EFI-7. The EFI shall measure the Spacecraft Potential with a time resolution better than the spin rate (3 seconds; from ESA to compute moments). Compliance. On-board spin-avg’d sphere potentials at 3 -s (spin-rate) resolution; EFI data rate allocation includes single spheres at ¼-rate of E-field data. IN. EFI-8. The EFI DFT Spectra Range shall be 16 Hz to 4 k. Hz, with df/f~25%. Compliance. Spectral products from DFB cover 8 Hz to 8 k. Hz at 5%, 10%, or 20% BW (16, 32, or 64 bins). Verified at DFB Functional Test. IN. EFI-9. The EFI shall measure DC-coupled signals of amplitude up to 300 m. V/m with 16 -bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified at DFB Functional Test. IN. EFI-10. The EFI shall measure AC-coupled signals of amplitude up to 50 m. V/m with 16 -bit resolution. Compliance. Analog gain and ADC resolution of DFB set accordingly. Verified at DFB Functional Test. THEMIS EOMP Review EFI Nov 19, 2009

Performance Requirements REQUIREMENT EFI DESIGN IN. EFI-11. The EFI noise level shall be below 10 -4 (m. V/m)/Hz 1/2. Compliance. Low-noise preamp chosen (OP-15); good analog design practices throughout preamp, BEB and DFB; CBE in Flight config is few times 10 -4 (m. V/m)/Hz 1/2. IN. EFI-12. The EFI HF RMS (Log power) measurement shall cover 100 -500 k. Hz with a minimum time resolution of the spin rate (on-board triggers). Compliance. Measured end-to-end gain of EFI sensors in the 100 -500 -k. Hz band is 0. 4; DFB provides HF-RMS at 1/16 to 8 samp/s. Verified at DFB Functional Test and Sci. Cal. IN. EFI-13. The EFI shall achieve an accuracy better than 10% or 1 m. V/m in the SC XY E-field components during times of onset. Compliance. See DC Error Budget Discussion. THEMIS EOMP Review EFI Nov 19, 2009

EFI Board Requirements REQUIREMENT EFI DESIGN DFB FUNCTIONAL REQUIREMENTS IN. DPU-36. The IDPU DFB shall provide an FFT Compliance. DFB design includes FPGA-based solution for determining the parallel and perpendicular projection (E dot B, E cross B) and FFT solutions. components of E and B in both fast survey and burst Verified through DFB Functional Test, and II&T testing. modes and produce spectra for each quantity separately. IN. DPU-37. The IDPU DFB shall integrate FGM digital data and EFI data to produce E·B. THEMIS EOMP Review Compliance. DFB design includes FPGA-based projection ( E dot B, E cross B) solutions. Verified through DFB Functional Test, and II&T testing. EFI Nov 19, 2009

EFI Board Requirements REQUIREMENT EFI DESIGN BEB FUNCTIONAL REQUIREMENTS IN. DPU-38. The IDPU BEB shall provide sensor biasing circuitry, stub and guard voltage control for the EFI. Compliance. The BEB design provides 3 independent bias channels per sensor (BIAS, GUARD, USHER) and one shared bias channel for the SPB sensors (BRAID). Boom deployment is provided through the IDPU/PCB and DCB. Verified during BEB Functional Test. IN. DPU-39. The IDPU BEB shall distribute a floating ground power supply to the EFI sensors. Compliance. The BEB design provides 6 independent floating grounds to the LVPS, and distributes the derived +/-10 -V analog supplies to the six EFI sensors. Verified during BEB Functional Test. IN. DPU-40. The IDPU BEB shall generate six independent BIAS, GUARD and USHER voltages with an accuracy of 0. 1% for distribution to the EFI sensors. Compliance. The BEB and EFI Preamp designs include matched gain-setting components, along with >12 -bit DAC, allowing accuracy of better than 0. 1%; Accuracy has been verified through BEB Functional Test and Sci. Cal. THEMIS EOMP Review EFI Nov 19, 2009

EFI Boom Requirements REQUIREMENT EFI DESIGN IN. BOOM-5 a. Deployed EFI Axials shall be repeatable and stable to Dq = 1 degree and DL/L = 1%. Compliance. Adequate stiffness and angular alignment of AXB stacers and deploy system included in design; verified by Vertical Deploy Test (0. 5 deg. And 1% typ. ). IN. BOOM-5 b. Length of deployed EFI Radials shall be repeatable and stable to Dq = 1 degree and DL/L = 1%. Compliance. Proper SPB cable design (limpness, CTE) along with std. Cable winding procedures included in design; verified by Vertical Deploy Test. IN. BOOM-6. EFI Axial Booms shall be designed to be deployed between 2 and 25 RPM about the Probe's positive Z axis. Compliance. Adequate stiffness and angular alignment of AXB stacers included in design; verified by Vertical Deploy Test. IN. BOOM-7. EFI Radial Booms shall be designed to be deployed between 2 and 25 RPM. Compliance. Adequate strength margins on cable included in design; verified by Pull Test (50 -lb. Proof load with electrical continuity check before, during and after loading). IN. BOOM-8. EFI Axial Booms deployed stiffness shall be greater than 0. 75 Hz (1 st mode). Compliance. Part of AXB stacer spec; verified by Stiffness Test; 1 st mode frequencies between 1. 5 and 2. 0 Hz. IN. BOOM-12. All deployed booms shall include TBD inhibits to prevent inadvertent release. Compliance. Test/Enable plugs included in design. Red tag AXB tube (AXB) covers, and Science-only Enable plugs. THEMIS EOMP Review EFI Nov 19, 2009

ON-ORBIT OPERATION AND CALIBRATION THEMIS EOMP Review EFI Nov 19, 2009

On-Orbit Current and Voltage Bias Sweeps “Sensor Diagnostic Test (SDT)” THEMIS EOMP Review EFI Nov 19, 2009

E vs. –Vx. B (EFI/FGM/ESA Inter. Calibration) THEMIS EOMP Review EFI Nov 19, 2009

E vs. –Vx. B (EFI/FGM/ESA Inter. Calibration) THEMIS EOMP Review EFI Nov 19, 2009

E vs. –Vx. B (EFI/FGM/ESA Inter-Calibration) THEMIS EOMP Review EFI Nov 19, 2009

Vsc vs. Ambient Density • THEMIS EOMP Review Typical two-slope correlation between Vsc and ambient ion density estimate (i. ESA). EFI Nov 19, 2009

MEASUREMENT CHALLENGES THEMIS EOMP Review EFI Nov 19, 2009

ES Cold Plasma Wake • Waveforms non-sinusoidal and significant amplitude (tens of m. V/m). • Shorter boom pair (E 34) has LARGER signal than long boom pair (E 12). • Occurrance consistent with ESA cold plasma observations, when available: – ne>ni – cold (few e. V) flowing ions present in i. ESA spectrum • Distortion reminiscent of cold plasma wake effect on Cluster [eg. Engwall et al. , 2006]. • Rate of occurrence on THEMIS is high; initial THEMIS EOMP Review estimates of 60 -80% of duskside passes. PIC simulation by Engwall & Eriksson (CLUSTER booms) EFI Nov 19, 2009

Short Booms: Axial E vs. Vsc • • • Significant correlation between v 56 (axial E-field) and Vsc over a broad range of spacecraft potentials (ambient densities) – ≈ 4 ((m. V/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!). THEMIS EOMP Review EFI Nov 19, 2009

What’s Calibration Error and What’s E||? THEMIS EOMP Review EFI Nov 19, 2009