Space Science Reviews

, Volume 141, Issue 1, pp 303–341

The Electric Field Instrument (EFI) for THEMIS

  • J. W. Bonnell
  • F. S. Mozer
  • G. T. Delory
  • A. J. Hull
  • R. E. Ergun
  • C. M. Cully
  • V. Angelopoulos
  • P. R. Harvey
Article

DOI: 10.1007/s11214-008-9469-2

Cite this article as:
Bonnell, J.W., Mozer, F.S., Delory, G.T. et al. Space Sci Rev (2008) 141: 303. doi:10.1007/s11214-008-9469-2

Abstract

The design, performance, and on-orbit operation of the three-axis electric field instrument (EFI) for the NASA THEMIS mission is described. The 20 radial wire boom and 10 axial stacer boom antenna systems making up the EFI sensors on the five THEMIS spacecraft, along with their supporting electronics have been deployed and are operating successfully on-orbit without any mechanical or electrical failures since early 2007. The EFI provides for waveform and spectral three-axis measurements of the ambient electric field from DC up to 8 kHz, with a single, integral broadband channel extending up to 400 kHz. Individual sensor potentials are also measured, providing for on-board and ground-based estimation of spacecraft floating potential and high-resolution plasma density measurements. Individual antenna baselines are 50- and 40-m in the spin plane, and 6.9-m along the spin axis.

The EFI has provided for critical observations supporting a clear and definitive understanding of the electrodynamics of both the boundaries of the terrestrial magnetosphere, as well as internal processes, such as relativistic particle acceleration and substorm dynamics. Such multi-point electric field observations are key for pushing forward the understanding of electrodynamics in space, in that without high-quality estimates of the electric field, the underlying electromagnetic processes involved in current sheets, reconnection, and wave-particle interactions may only be inferred, rather than measured, quantified, and used to discriminate between competing hypotheses regarding those processes.

Keywords

Electric field instrumentationElectrodynamicsReconnectionSubstorms

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • J. W. Bonnell
    • 1
  • F. S. Mozer
    • 1
  • G. T. Delory
    • 1
  • A. J. Hull
    • 1
  • R. E. Ergun
    • 2
  • C. M. Cully
    • 2
    • 3
  • V. Angelopoulos
    • 4
  • P. R. Harvey
    • 1
  1. 1.Space Sciences LaboratoryUniversity of CaliforniaBerkeleyUSA
  2. 2.Laboratory for Astrophysics and Space PhysicsUniversity of ColoradoBoulderUSA
  3. 3.Institute for Space PhysicsUppsalaSweden
  4. 4.Institute for Geophysics and Planetary PhysicsUniversity of CaliforniaLos AngelesUSA