Erlangen 2018 – scientific programme

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P: Fachverband Plasmaphysik

P 11: Helmholtz Graduate School - Poster

P 11.17: Poster

Tuesday, March 6, 2018, 16:15–18:15, Redoutensaal

Core temperature collapses driven by ECCD at W7-X stellarator — •Marco Zanini, Heinrich Laqua, Torsten Stange, Robert Wolf, and W7-X Team — Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, D-17491, Greifswald, Germany

The superconducting optimized stellarator Wendelstein 7-X is equipped with a flexible electron cyclotron resonance heating (ECRH) system, that allows up to 7 MW of power to be delivered to the plasma. A localized power deposition is possible and the ECRH itself can be used to drive a net current (ECCD). The negligible presence of toroidal currents makes W7-X a perfect testbed for ECCD experiments.

During ECCD operations, repetitive and periodic collapses of the central electron temperature have been observed; these collapses display a similar behavior to the well known "sawtooth oscillation" present in tokamaks.

An initial 1-D model has been developed to study the current diffusion in the plasma. An ECCD profile is simulated using the ray tracer code TRAVIS, developed at IPP. Due to Lenz's law a counter current is induced, whose time evolution is studied and analyzed. Local changes in the current density profile generate a local modification of the rotational transform, which can reach resonant values usually associated with appearance of plasma instabilities.

The characteristic timescale between the collapses is compared to the time needed by the rotational transform to reach the assumed resonant values.