Aachen PK 2003 – wissenschaftliches Programm

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P: Plasmaphysik

P 8: Magnetic Confinement

P 8.1: Vortrag

Dienstag, 18. März 2003, 15:30–15:50, FO2

Spatio-temporal behaviour of radiative instabilities in Wendelstein 7-AS stellarator — •Henning Thomsen and Ralf König — Max-Planck-Institut für Plasmaphysik, EURATOM Association, Germany

The island divertor experiments on the Wendelstein 7-AS (W7-AS) stellarator have sucessfully been completed. One highlight of the experimental campain was the access to a new improved operational regime, the HDH-mode [1]. In a few of the discharges of this type, a radiation belt forms on the inboard side of the torus and causes a degradation of the confined energy. Similar observations on tokamaks are attributed to a radiative instability, the so-called MARFE. Whereas in tokamaks these MARFEs often lead to an abrupt determination of the plasma (disruption) and should therefore be avoided, the consequences of the observed phenomenon in the W7-AS stellarator is generally less critical, and the energy confinement can recover when the radiation belt vanishes. One aim of this paper is to investigate the connection of the observed radiation belt with the MARFE phenomena as known from tokamaks. This connection was suggested in Ref. [2]. The main diagnostics are several cameras observing the plasma in the divertor target region, which measure in the light of H_α and C_II line radiation. A fast framing camera (frame rate up to 40.000 frames/s) was available during the experimental campain and provides data for studying the spatio-temporal behaviour of the radiation belt.

[1] K. McCormick, et al.,Phys. Rev. Lett. 89, 015001 (2002)

[2] U. Wenzel et al., Plasma Phys. Controlled Fusion, 44, L57 (2002)