Quasi-thermal noise spectroscopy in space plasmas

The transport of energy in space plasmas, especially in the solar wind, is far from being understood. Electrons are expected to play a major role for energy transport. Therefore, measuring accurately the temperature of the electrons and their non-thermal properties is essential to understand the transport properties of plasmas in non-local thermodynamic equilibrium. Quasi-thermal noise spectroscopy is a reliable tool for measuring in situ the electron temperature accurately since it is less sensitive to the spacecraft perturbations than particle detectors. This method uses a sensitive radio receiver connected to dipole antennas to measure the electrostatic fluctuations produced by the motion of charged particles in the surrounding plasma. This method has been successfully implemented on a number of spacecraft in various space plasmas. Spacecraft such as ISEE3/ICE, Ulysses, Wind, and STEREO have used or are still using quasi-thermal noise spectroscopy to measure the electron properties in the solar wind, a cometary trail, and the Jovian environment; while IMAGE used this method to study Earth´s magnetosphere, and Cassini continuously uses quasi-thermal noise spectroscopy in Saturn´s magnetosphere.