Geoscience Reference
In-Depth Information
wire with a sphere at the end of the wire. It is directly fed to the pre-
amplifiers located inside the spacecraft. It responds to frequencies from DC
to 10 MHz. The other pair of electric field sensor is MEFISTO, based on
heritage from the EFW aboard the Cluster spacecraft.
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It consists of an
extendable boom, a conductive short wire with a sphere at the end, and
a pre-amplifier box. The preamplifier box is attached at the end of the
extendable boom and the short wire with the sphere is deployed from that
preamplifier box. The antenna has good response in the frequency range
below 3 MHz.
Two sets of magnetic field sensors are installed at the end of the coil-
able mast, 5 m in length, in order to avoid electromagnetic contamination
radiated from the spacecraft. The LF-SC is two-axial search coils. They are
mounted in the spacecraft spin plane, and observe electromagnetic waves
in the frequency range below 20 kHz. The dual-band search coil (DB-SC)
is a single-axis search coil. It covers two different frequency ranges (one is
below 20 kHz, and the other is up to 640 kHz). It is aligned with the space-
craft spin axis. Two different coils with different turn numbers are wound
on one axis core. These two different coils provide frequency coverage in
two different ranges.
The sensitivities of electric field and magnetic field sensors are shown
in Fig. 4.
3.2.
Receivers for electric field and magnetic field
EWO-EFD is dedicated to observing DC and low-frequency electric fields.
It is connected to the WPT and MEFISTO electric field sensors. The fre-
quency coverage of the EWO-EFD is from DC to 30 Hz, and its dynamic
range is 110 dB. The EWO-EFD also has a single probe system for mea-
suring spacecraft potentials.
The EWO-WFC/OFA receiver components focus on plasma wave obser-
vations in the medium frequency range up to 360 kHz for electric field, and
up to 20 kHz for magnetic field. Waveforms picked up by electric/magnetic
field sensors are directly sampled (WFC data) and stored in onboard mem-
ories. The stored waveform data are used for calculating FFT spectra (OFA
data). While the OFA data are sent to Earth in the nominal mode, the WFC
waveform data are sent after the data selection and data compression pro-
cedures in the high bit rate mode. SORBET has two main functions. One
is as thermal noise receiver (TNR), which measures
in situ
plasma temper-
atures and densities by monitoring continuously the plasma thermal noise.
