Göttingen 2025 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 17: Poster Session II

P 17.24: Poster

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

Investigation of Wendelstein 7-X Scrape-Off Layer Characteristic by Helium Line Ratio Spectroscopy — •Foisal B.T. Siddiki^1,2, Oliver Schmitz², Maciej Krychowiak¹, Erik Flom³, Frederik Henke¹, Dorothea Gradic¹, and W7-X team¹ — ¹Max Planck Institute for Plasma Physics, Germany — ²University of Wisconsin-Madison, USA — ³Thea Energy, USA

Heat and particle transport in the Wendelstein 7-X(W7-X) scrape-off layer (SOL) significantly influences the performance of its divertor, which serves as the heat and particle exhaust system. To optimize the divertor concept, it is essential to understand the transport phenomena within the SOL, which can be achieved by studying plasma parameters like electron temperature (T_e) and the density (n_e). As a way of measuring the basic plasma parameters in the W7-X SOL, the diagnostic systems used consist of a gas injection system and multiple spectrometers with different spectral resolutions. They observe one upper and one lower divertor unit (downstream position) and for the first time also in the midplane area (upstream position). Line ratio spectroscopy based on a collisional radiative model of atomic helium is used to infer n_e and T_e. The helium beam diagnostic at W7-X has been thoroughly validated and widely utilized to map plasma parameters within the island divertor. The T_e , n_e profiles presented here in this work were measured using all three systems under various conditions, including detached and impurity-seeded plasmas. A comparison of the T_e , n_e profiles obtained at the downstream and upstream positions will be presented.

Keywords: Wendelstein 7-X (W7-X); He line ratio spectroscopy; Island Divertor