THEMIS Engineering Peer Review 1 UCB, October 15-16, 2003 Electric Field Instrument (EFI) Operational Concept

THEMIS Engineering Peer Review 2 UCB, October 15-16, 2003 Operational Concept (1) Deployment and Commissioning P3-P5 EFI deployed ~Launch+1 mo., after initial orbit placement. P1-P2 EFI deployed ~Launch+3 mo., after raise to final orbits, one month prior to beginning of science season (WD-90). On-board DC functional test to ensure state-of-health of EFI on P1 and P2 prior to ascension. SPB deployed alternately in pairs to 5, 10, 12, 14, 16, and 18 m. Each deploy step takes less than 20 min. (fits max. contact duration of 30 min.). AXB deployed singly, on same orbit if no anomaly (TBR). Sphere potentials, differential E-field, and housekeeping data taken in Diagnostic Mode (TBD) to allow monitoring of deployment, EFI system response, and SC potential structure. Multiple Slow Sweeps of EFI bias settings (~1 hr duration) run on orbit after deploy step to probe EFI system response and allow for bias optimization. Data taken in Diagnostic Mode. After deploy, Slow Sweeps scheduled with TBD cadence to update biasing as sensor surface properties stabilize.

THEMIS Engineering Peer Review 3 UCB, October 15-16, 2003 Operational Concept (2) Operations Slow Sweeps and diagnostic data taken several times per year, upon first entry into a new plasma regime, and after long-duration eclipses to maintain optimal bias settings and monitor EFI state-of-health. EFI instrument mode set by ~30 registers on BEB; a typical mode will be specified with ~200 commands, valid over a typical one month period, once deploy and commissioning are completed. Data Validation Both sphere potentials and differential E-field data gathered in all waveform modes, allowing for initial verification of E- field data. Intercomparison of Eperp and –VxB from ESA and FGM to establish offsets and boom shorting effects.

THEMIS Engineering Peer Review 4 UCB, October 15-16, 2003 Operational Concept (3) Data Rates Slow Survey –Spin-fit radial and axial E-fields; SC potential (via ptcls). –Filter Banks. Fast Survey –3 E-field at 32 S/spin; 2-3 sphere potentials at 8 S/s. –Filter Banks and FFT spectra. Particle Burst –3 E-field at 128 S/s; 2-3 sphere potentials at 32 S/s. –Filter Banks and FFT spectra. Wave Burst –3 E-field at 1024 or 4096 S/s; 2-3 sphere potentials at 256 or 1024 S/s. –Filter Banks and FFT spectra. Diagnostic Mode (TBR) –E-field and sphere potentials at >= 16 S/s. –Bias control levels at >= 1 S/s.