Erlangen 2026 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 21: Codes and Modeling II

P 21.2: Hauptvortrag

Freitag, 20. März 2026, 09:30–10:00, KH 01.013

Microwave cavity resonance spectroscopy: a novel approach for spatially resolved electron density measurements — •Jens Oberrath — Modeling and Simulation, South Westphalia University of Applied Sciences, Soest, Germany

Electron density is a critical parameter of plasma. Its non-invasive measurement becomes particularly challenging when spatial resolution is required. A promising technique for this purpose is Microwave Cavity Resonance Spectroscopy (MCRS), where electromagnetic waves are coupled into a plasma-filled cavity to excite resonances. These resonances, which also occur in vacuum, are shifted by the presence of the plasma. MCRS has been known since the 1950s. While significant improvements have been made over the past few decades, a robust approach for measuring spatially resolved electron densities has yet to be fully developed. The scattering behavior of a plasma-filled cavity with a finite number of connected waveguides can be described by the shell-model approach developed by Mahaux and Weidenmüller. Using functional analytic methods, the scattering matrix S for such a cavity can be derived. Assuming a cold plasma model for the electrons, the calculated elements of S (reflection and transmission coefficients) contain the spatially dependent electron density. For a specific type of plasma, a density profile can be assumed and expanded as a function with a certain number of unknown parameters. By comparing the calculated elements of S with the measured ones, these unknown parameters in the density profile can be determined, enabling the spatially resolved measurement of electron densities.

Keywords: microwave cavity resonance spectroscopy; active plasma resonance spectroscopy; functional analytic methods; scattering matrix; spatial dependent electron density measurement