BackForwardInstrument:  EFI (THEMIS) 

Instrument details
Acronym EFI (THEMIS)
Full name Electric Field Instrument
Purpose To measure electric fields in Earth's dynamic magnetosphere to determine plasma flows and electromagnetic waves associated with substorm onset
Short description Using four probes, approximately 25-m long wire cables and two 3-m long stiff telescopic booms on each probe, to measure the electric fields in three independent directions. Dynamic range: 0.1-1000 mV/m
Background Part of a package of instruments to study the Magnetosphere
Scanning Technique 5 satellites moving to different positions into the Magnetosphere for 3-D field reconstruction
Resolution N/A
Coverage / Cycle Full magnetosheric volume; sampling at 25 ms intervals
Mass 13 kg Power 1 W Data Rate


Providing Agency NASA
Instrument Maturity Flown on an R&D satellite
Utilization Period: 2007 to 2024
Last update: 2021-12-07
Detailed characteristics
Satellites this instrument is flying on

Note: a red tag indicates satellites no longer operational, a green tag indicates operational satellites, a blue tag indicates future satellites

Instrument classification
  • Solar and space environment monitors
  • Field or radiowave sensor
WIGOS Subcomponents
  • Subcomponent 2
  • Magnetospheric energetic particles and magnetometers
  • Electric field sensor [in LEO and cross magnetosphere]
  • Ionospheric electron density sensor [in LEO and cross magnetosphere]
  • Ionospheric plasma density
Mission objectives
Primary mission objectives
  • Electric Field
Evaluation of Measurements

The following list indicates which measurements can typically be retrieved from this category of instrument. To see a full Gap Analysis by Variable, click on the respective variable.

Note: table can be sorted by clicking on the column headers
Note: * Primary mission objective.
VariableRelevance for measuring this variableOperational limitationsExplanation
Electric Field*1 - primaryNo specific limitation.Cluster in the magnetosphere. Electric field, wide dynamic range