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P: Fachverband Plasmaphysik

P 9: Poster I

P 9.26: Poster

Dienstag, 29. März 2022, 16:00–17:30, P

Magnetic signature of ECCD induced crashes in the Wendelstein 7-X stellarator — •K. Rahbarnia, S. Vaz Mendes, C. Brandt, H. Thomsen, J. Schilling, K. Aleynikova, C. Slaby, A. Könies, and W7-X Team — Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany

Wendelstein 7-X is a stellarator-type fusion experiment. A strong toroidal plasma current is not needed for optimized confinement properties. Nevertheless, during the last operation campaign a number of experiments including an externally driven plasma current were conducted. The so-called electron cyclotron current drive (ECCD) was used to counteract any rising bootstrap current to completely nullify it. Alternatively, in the presence of co-driven ECCD, the increase of a naturally evolving bootstrap current was accelerated so that an equilibrated state could be reached faster. During ECCD experiments crashes in global plasma parameters have been observed, which sometimes even led to a total collapse of the plasma. Previous analysis mainly involving fast changes of the measured electron temperature caused by the crashes revealed a sawtooth-like behaviour similar to tokamaks. In this study the magnetic signature of these crash events measured by poloidal arrangements of in-vessel Mirnov coils is investigated generally supporting the previous results. Various ECCD scenarios are studied showing similar frequency (around 40kHz) and poloidal mode number (m<5) of the observed bursty magnetic fluctuations. The results are compared to theoretical predictions using the magnetic equilibrium code VMEC and the MHD continuum code CONTI.