Spatio-Temporal Analysis of Magnetic Field Fluctuations (STAFF)

Description

This experiment (STAFF: Spatio-Temporal Analysis of Field Fluctuations) is one of the five complementary experiments which form the Wave Experiment Consortium (WEC) on Cluster. STAFF consists of: (1) a triaxial boom-mounted search-coil magnetometer to measure the magnetic components of electromagnetic fluctuations (up to 4 KHz); and, (2) a spectrum analyzer to compute the 25 auto- and cross-correlation coefficients of the spectral matrix, using three magnetic and two electric components of the waves. The magnetic waveform (up to either 10 Hz or 180 Hz) is also transmitted. The Z-axis sensor is parallel to the spacecraft spin axis. Each sensor consists of a high-permeability core embedded inside two solenoids. The frequency response of the main winding is flattened by a secondary winding through a flux feedback effect, in the range 40--4000 Hz. Further, the secondary winding is used as a calibration loop to which an external AC signal is applied. In normal bit rate the wave-form data cover the 0.1--10 Hz frequency range, and the spectrum analyzer covers the range 8 Hz to 4 KHz. In high bit rate, the wave-form data cover 0.1--180 Hz and the spectrum analyzer covers 64 Hz to 4 KHz, using only the two highest frequency bands. In the base mode in normal bit rate the auto-spectra are averaged over 1 s, and the complete 25-component matrix is averaged over 4 s for five components. In high bit rate, only the two highest frequency bands are analyzed. In the fast modes, time resolution is 1 s for the cross-spectra, and either 0.125 s or 0.25 s for the auto-spectra. Other modes are also defined. The analysis will also use electric field waveform data from the EFW (part of WEC), and the hardware of the two instruments was designed to optimize correlation: low-pass filters are identical, sampling frequency is the same, and there is a synchronization signal for simultaneous sampling. The output signals of the STAFF magnetic preamplifiers are also sent to two other instruments: the WBD (part of WEC) and the EDI. Some of the magnetospheric structures to be studied are of small scale, and where the signature duration is of the order 1 s or less, the STAFF search coil data are complementary to those of the fluxgate magnetometer (FGM). For more details of the Cluster mission, the spacecraft, and its instruments, see the report ``Cluster: mission, payload and supporting activities,'' March 1993, ESA SP-1159, and the included article ``The STAFF (Spatio-Temporal Analysis of Field Fluctuations) Experiment for the Cluster Mission'', by N. Cornilleau-Wehrlin et al., from which this information was obtained.