THE ELECTRIC-FIELD AND WAVE EXPERIMENT FOR THE CLUSTER MISSION

The electric-field and wave experiment (EFW) on Cluster is designed to measure the electric-field and density fluctuations with sampling rat es up to 36 000 samples s(-1). Langmuir probe sweeps can also be made to determine the electron density and temperature. The instrument has several important capabilities. These include (1) measurements of quas i-static electric fields of amplitudes lip to 700 mV m(-1) with high a mplitude and time resolution, (2) measurements over short periods of t ime of up to five simualtaneous waveforms (two electric signals and th ree magnetic signals from the seach coil magnetometer sensors) of a ba ndwidth of 4 kHz with high time resolution, (3) measurements of densit y fluctuations in four points with high time resolution. Among the mor e interesting scientific objectives of the experiment are studies of n onlinear wave phenomena that result in acceleration of plasma as well as large- and small-scale interferometric measurements. By using four spacecraft for large-scale differential measurements and several Langm uir probes on one spacecraft for small-scale interferometry, it will b e possible to study motion and shape of plasma structures on a wide ra nge of spatial and temporal scales. This paper describes the primary s cientific objectives of the EFW experiment and the technical capabilit ies of the instrument.