Greifswald 2024 – scientific programme

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P: Fachverband Plasmaphysik

P 25: Poster III

P 25.10: Poster

Thursday, February 29, 2024, 16:30–18:30, ELP 6: Foyer

Dynamics of impurity injection events in Wendelstein 7-X stellarator analysed by tomography — •Henning Thomsen, Thomas Wegner, Christian Brandt, Charlotte Büschel, Sara Mendes, Kian Rahbarnia, and W7-X team — Max-Planck Institute for Plasma Physics, Greifswald, Germany

The soft-X-ray tomography system [1] installed in the Wendelstein 7-X stellarator is capable of tracing the spatio-temporal dynamics of plasma perturbations in a poloidal plasma cross-section. The diagnostic has more than 300 lines of sight and a high bandwidth of more than 100 kHz. In this contribution we analyse the dynamics of a laser blow-off injection [2] of a high-Z impurity species into the plasma by means of tomographic inversion of the line-integrated soft-X-ray data. A singular value decomposition of the time sequence of tomographic images clearly shows the poloidal motion of the perturbation following the injection. We find that the propagation is following the direction of the ExB-rotation of the core plasma (the radial electric field in stellarators is predominantly governed by neoclassical transport processes). For sufficiently small plasma perturbation, this technique could be used to experimentally constrain the estimation of the radial electric field profile.

[1] C Brandt et al., Plasma Phys. Control. Fusion 62 (2020) 035010

[2] Th. Wegner et al., Rev. Sci. Instrum. 89 (2018) 073505

Keywords: Stellarator; Wendelstein 7-X; Tomography