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P: Fachverband Plasmaphysik

P 25: Poster III

P 25.29: Poster

Donnerstag, 29. Februar 2024, 16:30–18:30, ELP 6: Foyer

In-situ spectral calibration of the Thomson scattering system at W7-X using Rayleigh scattering — •Jannik Wagner, Golo Fuchert, Ekkehard Pasch, Jens Knauer, Kai Jakob Brunner, Sergey A. Bozhenkov, Marcus Beurskens, Matthias Hirsch, Robert C. Wolf, and W7-X Team — Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald

In most high temperature fusion experiments, Thomson scattering is one of the main diagnostics for measuring electron temperature and density. So far, the spectral calibration at W7-X uses the light of a supercontinuum laser in combination with a monochromator scattered diffusively by a plate in front of the observation optics. Using this approach, however, the window between the plasma vessel and the observation optics is not part of the calibration and its transmission can vary during an experimental campaign due to coating.

To overcome these issues, a new in-situ calibration has been developed in recent years. Using an optical parametric oscillator (OPO), Rayleigh scattering inside the plasma vessel acts as tunable volumetric light source that can be observed with the exact same setup used for the Thomson scattering measurements. A proof-of-principle was demonstrated in 2018/19, but so far the quality was not sufficient to replace the existing calibration method.

In this work, improvements of the optical setup and in particular a more reliable energy measurement are presented. These measures reduce the experimental uncertainties in a new Rayleigh scattering experiment from which improved calibration curves could be determined.

Keywords: plasma physics; laser phyiscs; plasma diagnostics; Thomson scattering; optical parametric oscillator