Plasma diagnostic measurements for linear to weakly non-linear plasma response: application to Mutual Impedance experiments and Relaxation Sounders

Luca Bucciantini

Relaxation sounder experiments and mutual impedance experiments are popular plasma diagnostic techniques for the determination of characteristic plasma parameters. Both experiments consist of: exciting the local plasma medium over a given frequency range, with a succession of sinusoidal signals at a fixed frequency and measuring the electric field generated in the plasma at this same frequencies, from which an electric power spectrum is built. Such spectra typically exhibit resonances at the characteristic frequencies of the probed plasma. Active instruments for in situ plasma diagnostics emitting signals at energies comparable to the local electron energy are expected to trigger non-linear plasma responses, modifying locally the probed plasma dielectric. This study aims at investigating the impact of high emission levels to the instrumental response of relaxation sounders and mutual impedance experiment that might introduce non-linear plasma responses.