Mutual impedance experiments and quasi-thermal noise spectroscopy are two in situ plasma diagnostic techniques. They both rely on electric antennas in contact with the plasma, and both measure electron properties, notably electron density and temperature. They differ in that mutual impedance is an active technique, while quasi-thermal noise is a passive technique. Mutual impedance experiments measure the mutual impedance spectrum between two antennas. This measurement is performed by generating an electric perturbation within the plasma using one antenna, while another antenna simultaneously measures the electric field. Quasi-thermal noise spectroscopy uses one dipolar antenna, connected to a sensitive radio receiver, that measures the electric field fluctuations produced by the thermal motion of the ambient particles of the plasma.

Both techniques are included in the scientific payload of past, current, and future NASA, ESA, and JAXA space missions, such as Rosetta, Parker Solar Probe, BepiColombo, JUICE, and Comet Interceptor. 

Instrumental models for both techniques are needed to interpret the instrumental output and derive measurements of the electron properties. They take into account both the electron plasma dispersion function and the geometry of the instrument. The modelling current state-of-the-art is largely focused on the limit of an unmagnetized plasma, that in this context identifies a plasma where the ratio of plasma to electron cyclotron frequency is much larger than one. We highlight here that the magnetized plasma regime will be of interest for future planetary space missions, including BepiColombo and JUICE, and to prepare future mission in the Earth's magnetosphere.

In this context, we provide for the first time a complete diagnostic, in magnetized plasmas, of the plasma electron density and temperature, and the magnetic field magnitude and direction, based on mutual impedance experiments and quasi-thermal noise spectroscopy.

For this purpose, we developed numerical models for both mutual impedance experiments and quasi-thermal noise spectroscopy in a magnetized plasma. A diagnostic is derived for the plasma density, the electron temperature, and the magnetic field. We validated these instrumental models against both laboratory and space measurements. The dependency of this diagnostic on the antenna shape and size is investigated, as well as the expected precision of these techniques as plasma diagnostic.