Measuring Plasma Parameters With Thermal Noise Spectroscopy

Abstract

This paper describes the basic principles, the unique features and the limitations of thermal noise spectroscopy as a tool for in situ diagnostics in space plasmas. This technique is based on the analysis of the electrostatic field spectrum produced by the quasi-thermal fluctuations of the electrons and ions, which can be measured with a sensitive wave receiver at the terminals of an electric antenna. This method produces routine measurements of the bulk electron density and temperature, and is being extended to measure the ion bulk speed. It has the advantage of being in general relatively immune to spacecraft potential and photoelectron perturbations, since it senses a large plasma volume. We compare this method to other techniques, and give examples of applications in the solar wind as well as in cometary and in magnetized planetary environments.