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Instrument: EFI : Electric Fields Investigation
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The Electric Field Instrument (EFI) on the Polar spacecraft measures the three
components of the ambient vector electric field and the thermal electron

The electric field and plasma density measurements are made over a frequency
range of DC to above 20 kHz. The dynamic range of the electric field
measurement is 0.02 to 1000 mV/m, while the plasma density will be measured at
least over the range of 0.1 to 100 particles per cubic centimeter. A by-product
of the experiment is measurement of the floating potential of the spacecraft
over the range of about +1 to +90 volts.

An important component of the Electric Field Instrument is a two megabyte burst
memory that allows storage of high time resolution field and plasma density
measurements, allowing study of rapid variations of non-linear spatial
structures and waves.

The EFI sensors are arranged as three orthogonal sphere pairs whose potential
differences and Langmuir probe characteristics are measured. Two of these
sphere pairs are in the satellite spin plane on the ends of wire booms that
provide tip to tip sphere separations of 100 and 130 meters respectively, while
the third pair is aligned along the spacecraft spin axis with a 14 meter tip to
tip separation that is provided by rigid stacer booms.

The electric field preamplifiers have frequency responses to above one mHz to
accommodate their use by the Plasma Wave Instrument. In addition, the Electric
Field Instrument interfaces on the spacecraft with the Magnetic Field
Expirement (which provides information for deciding when to trigger bursts of
data collection), the Hydra plasma experiment (in order that both instruments
collect high time resolution data simultaneously), and the low energy plasma
experiment, Tide, (which wants to know when the Electric Field Instrument is
collecting data in the burst mode).

The heritage for the Electric Field Instrument encompasses instruments
previously flown on the S3-3, GEOS, ISEE-1, Viking, and CRRES satellites, as
well as experiments being built for the Freja, FAST, and Cluster satellites.

Harvey, P., F. S. Mozer, D. Pankow, J. Wygant, N. C. Maynard, H. Singer, W.
Sullivan, P. B. Anderson, R. Pfaff, T. Aggson, A. Pedersen, C. G. Falthammar,
Science Reviews 71: 583-596, 1995.

For more information, see:

Online Resources

Instrument Logistics
Instrument Start Date: 1996-02-24
Instrument Owner: NASA