Mainz 2022 – scientific programme

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P: Fachverband Plasmaphysik

P 14: Plasma Wall Interaction II / HEPP III

P 14.3: Talk

Wednesday, March 30, 2022, 16:30–16:45, P-H12

Surface charge diagnostics by infrared multiple internal reflection spectroscopy — Kristopher Rasek, •Franz Xaver Bronold, and Holger Fehske — Institut für Physik, Universität Greifswald, 17489 Greifswald, Germany

We propose to measure the surface (wall) charge accumulating at a floating plasma-dielectric interface via infrared multiple internal reflection spectroscopy [1]. The negative charge deposited into the plasma-facing dielectric, forming the negative part of an electric double layer (the positive part being the plasma sheath), leads to a change of the reflection coefficient, when the interface is subjected to infrared radiation. Based on the Boltzmann equations for the charge kinetics of the double layer and nonlocal surface response functions to calculate the reflection coefficient in the presence of the charge inhomogeneity at the plasma-solid interface, we show theoretically and numerically that a local, Drude-like expression is in fact sufficient to describe the optical response. It contains only the integrated surface charge, enabling thus a straightforward analysis of measured data. To amplify the charge-induced change in the reflectivity, we suggest an experimental setup utilizing the plasma-solid interface as a multiple internal reflection element. Numerical results indicate that in such a setup the magnitude of the wall charge can directly be determined from the change it causes in the transmitivity of the optical element. [1] K. Rasek, F.X. Bronold, and H. Fehske, Phys. Rev. E 104, 015204 (2021)