Göttingen 2025 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 17: Poster Session II

P 17.14: Poster

Mittwoch, 2. April 2025, 16:15–18:15, ZHG Foyer 1. OG

Frequency-sweeping calibration source for the dual-frequency CTS radiometer at W7-X — •Daniel Straus, Dmitry Moseev, Sergiy Ponomarenko, Laurent Krier, Heinrich Laqua, Stefan Marsen, and Torsten Stange — Max-Planck-Institut für Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald, Germany

The Collective Thomson Scattering (CTS) diagnostic at the Wendelstein 7-X stellarator must be calibrated. The current calibration process involves using two thermal sources, one roughly at room temperature and the other at -196 C (boiling point of nitrogen), with the black body radiation emitted by each source being significantly different. The CTS receiver works at two frequency bands: 138.5-141.5 GHz and 171-177 GHz, and it is important that the receiver is absolutely calibrated in both bands. These black body sources produce weak signals which require hours long averaging times in order to achieve an acceptable signal-to-noise ratio. With such time scales, the receiver electronics experience systematic drifts which also need to be accounted for, making the overall calibration procedure long and cumbersome. In this contribution, we will discuss the design and first results of a new sweeping calibrator that replaces the black body sources. This calibrator consists of a tunable continuous wave THz source, followed by attenuators, waveguide switches and a directional coupler, which splits the incoming signal into two distinct power levels. The THz source and other components are carefully characterized to protect receiver electronics from high power. The calibration tool is integrated with the CTS receiver and allows quick semi-automatic calibration.

Keywords: Stellarator; Collective Thomson Scattering; Wendelstein 7-X; Diagnostics; Calibration