Plasma Diagnostics

In order to supervise plasma processes, a number of invasive and non-invasive diagnostic methods is applied. The probably best known diagnostic tool is the Langmuir probe, which is an invasive and active diagnostic tool. With this tool, fundamental plasma parameters like plasma densitiy and temperature of the electrons can be measured. Non-invasive methods are, for instance, optical measuring methods like the optical emission spectroscopy, with which the plasma is analysed and observed from outside through a window.

At the Chair of Theoretical Electrical Engineering, a new active diagnostic tool is developed and theoretically chracterised: the multipole resonance probe, MRP. The MRP provides diagnostic data by getting the resonance frequency of the plasma measured. To do so, a high frequency voltage is applied to the MRP in the plasma. However, due to its low inertia, the fast oscillation of the voltage can only be perceived by electrons. Through a sweep of the applied frequency it is possible to measure a resonance curve, which enables quantitative conclusions about the density and temperature of electrons as well as the collision frequency. 

The development of the MRP is pushed as a planar (2D) and as a spheric (3D) version. An advantage of the planar MRP is the possibility to integrate it in the wall of the plasma chamber as a minimally invasive diagnostic tool.