No abstract

Abstract. Highlights are presented from studies of the electric field data from various regions along the CLUS-TER orbit. They all point towards a very high coherence for phenomena recorded on four spacecraft that are separated by a few hundred kilometers for structures over the whole range of apparent frequencies from 1 mHz to 9 kHz. This presents completely new opportunities to study spatialtemporal plasma phenomena from the magnetosphere out to the solar wind. A new probe environment was constructed for the CLUSTER electric field experiment that now produces data of unprecedented quality. Determination of plasma flow in the solar wind is an example of the capability of the instrument.

Abstract. For accurate measurements of electric fields, spherical double probes are electronically controlled to be at a positive potential of approximately 1 V relative to the ambient magnetospheric plasma. The spacecraft will acquire a potential which balances the photoelectrons escaping to the plasma and the electron flux collected from the plasma. The probe-to-plasma potential difference can be measured with a time resolution of a fraction of a second, and provides information on the electron density over a wide range of electron densities from the lobes (∼ 0.01 cm −3 ) to the magnetosheath (> 10 cm −3 ) and the plasmasphere (> 100 cm −3 ). This technique has been perfected and calibrated against other density measurements on GEOS, ISEE-1, CRRES, GEOTAIL and POLAR. The Cluster spacecraft potential measurements opens the way for new approaches, particularly near boundaries and gradients where four-point measurements will provide information never obtained before. Another interesting point is that onboard data storage of this simple parameter can be done for complete orbits and thereby will provide background information for the shorter full data collection periods on Cluster. Preliminary calibrations against other density measurements on Cluster will be reported.

Electron density fluctuations are regularly observed near the plasmapause together with electromagnetic waves below the electron cyclotron frequency (usually called hiss or chorus). Instruments on board CLUSTER spacecraft often observe two such emission bands with fluctuating wave intensities that suggest wave ducting in density enhancements as well as troughs. Near perigee the CLUSTER density measurements are usually limited to the electron density from 0.2 to 80 cm−3. To establish a correlation between density and wave intensity deeper inside the outer plasmasphere, we extrapolate the electron density from the spacecraft potential after fitting a relationship between observed plasma frequency and spacecraft potential. During a plasmapause crossing on June 5, 2001 (near the geomagnetic equator, L = 4 − 6, afternoon sector), density fluctuations up to hundreds cm−3 are found while whistler mode waves are observed in two separate frequency bands, at 100–500 Hz (correlated to the density fluctuations) and 3–6 kHz (anti‐correlated).

The main objective of the Mutual Impedance Probe (MIP), part of the Rosetta Plasma Consortium (RPC), is to measure the electron density and temperature of Comet 67P/ChuryumovGerasimenko's coma, in particular inside the contact surface. Furthermore, MIP will determine the bulk velocity of the ionised outflowing atmosphere, define the spectral distribution of natural plasma waves, and monitor dust and gas activities around the nucleus. The MIP instrumentation consists of an electronics board for signal processing in the 7 kHz to 3.5 MHz range and a sensor unit of two receiving and two transmitting electrodes mounted on a 1-m long bar. In addition, the Langmuir probe of the RPC/LAP instrument that is at about 4 m from the MIP sensor can be used as a transmitter (in place of the MIP ones) and MIP as a receiver in order to have access to the density and temperature of plasmas at higher Debye lengths than those for which the MIP is originally designed.