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THEMIS Electric Field Instrument (EFI) Dr. John Bonnell Space Sciences Laboratory UC Berkeley. Performance vs. Specifications. EFI has met or exceeded on-orbit performance requirements and specifications (all requirements and specs included in appendix):

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  • THEMIS

  • Electric Field Instrument (EFI)

  • Dr. John Bonnell

  • Space Sciences Laboratory

  • UC Berkeley


Performance vs specifications
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.


Assessment of data products 1
Assessment of Data Products (1)

  • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-1 to -4):


Assessment of data products 2
Assessment of Data Products (2)

  • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-5 to -10):


Assessment of data products 3
Assessment of Data Products (3)

  • L1 EFI data products are sufficient to meet Level-1 Science Requirements (EFI-11 to -13):


Assessment of data products 21
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).


Data maturity 1
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.


Data maturity 2
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.


Efi lessons learned
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.


  • BACKUP SLIDES:

  • References.

  • Requirements and Specs.

  • On-Orbit Operation and Calibration.

  • Measurement Challenges.


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.




Cleanliness; Elect., Mech. ICD










On-Orbit Current and Voltage Bias Sweeps

“Sensor Diagnostic Test (SDT)”


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


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


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


Vsc vs ambient density
Vsc vs. Ambient Density

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



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)


Short booms axial e vs vsc
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!).



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