STAFF and WHISPER Waves measurements instruments

STAFF

The STAFF experiment (Spatio-Temporal Analysis of Field Fluctuations) is designed for spatio-temporal analysis of fluctuations of the magnetic and electric fields.

It comprises sensors for measuring magnetic fluctuations, a waveform analyser and a spectrum analyser. The sensors form a three-axis system measuring the fluctuations of the magnetic field from 0.1 Hz to 4 kHz. The corresponding signals are either transmitted in waveform or processed by the analyser, which processes the two electrical components from the EFW experiment and the magnetic components of STAFF, and computes the autocorrelations and cross-correlations of these five components.

On the left, the three-axis antennas in their thermal blanket, in the middle the preamplifier, and on the right the electronic unit: the lower part corresponds to the spectrum analyser, and the upper part to the waveform analyser.

Main characteristics

• Three-axis magnetic sensor with flux reverse feedback on a 5 metre boom
• Sensitivity: 5x10^-3 nT Hz^-½ at 1 Hz, 4x10^-5 nT Hz^-½ at 100 Hz and at 4 kHz
• Waveform measurement up to 10 or 180 Hz depending on the telemetry mode, with a dynamic range of 96 dB.
• Spectrum analyser:
  
  • spectrum measurement up to 4 kHz over three bands:
    On each band, computation of the Fourier coefficients over nine sub-bands at logarithmic intervals.
    • band A: 8-64 Hz
    • band B: 64-512 Hz
    • band C: 512-4000 Hz
  • 135 auto-spectra and 270 inter-spectra for phase computation. Temporal resolution depends on the selected mode, varying from 125 ms to 1 second and from 1 to 4 seconds respectively.
  • Dynamic range: 96 dB.

WHISPER

The WHISPER instrument (Waves of HIgh frequency Sounder for Probing the Electron density by Relaxation) is designed to measure an electrical component of the waves up to 80 kHz and to determine the density of the plasma by "sounding".

A relaxation sounder is used to determine the density of the plasma by transmission (active sounder) and receiving sequences (passive sounder). The transmitter sends out short pulses at variable centre frequencies to excite the plasma resonances: after each transmission, the receiving part of the instrument is activated to detect any echoes within a narrow band.

From the echoes located at characteristic frequencies, the density of the plasma can be deduced, since this is proportional to the square of the plasma frequency, which is one of the resonances that the sounder can excite.

Main characteristics

• Measurement of electronic densities between 0.2 and 80 particles per cubic centimetre with 1% accuracy, temporal resolution between 1.5 and 28 seconds.
• Measurement of the natural waves of plasma between 2 and 80 kHz with a sensitivity of 2 nV m^-1 Hz ^-½ , temporal resolution between 320 ms and 2.15 seconds.
• Instrument mass: 2 kg
• Consumption: 2.7 to 3 W depending on operating conditions.

It is not possible to describe all the operating modes of the STAFF and WHISPER experiments here. The various modes provided aim to optimize all measurements of the wave consortium (WEC) according to the region crossed.