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Role of convective amplification of $$n$$=1 energetic particle modes for N-NB ion dynamics in JT-60U

Bierwage, A.; Shinohara, Koji; Aiba, Nobuyuki; Todo, Yasushi*

The hybrid code MEGA is used to simulate an Abrupt Large-amplitude Event (ALE) in JT-60U. The goal is to look for a threshold with respect to the fast ion beta beyond which Energetic Particle Modes (EPM) undergo convective amplification and cause significant fast ion transport. This is motivated by the hypothesis that such a threshold may work as a trigger mechanism for relaxation events, such as ALE. In order to facilitate quantitative comparisons with the experiment, a realistic geometry, bulk pressure and fast ion distribution are used. Consistently with the experiment, the simulation predicts a burst time of about 0.3 ms and peak magnetic fluctuation levels $$delta$$$$beta$$$$_{vartheta}$$/$$beta$$$$<$$10$$^{-3}$$ at the plasma boundary. As $$beta$$$$_{h0}$$ is increased, a gradual (not sharp) increase in the convective amplification of the EPM and in the convective transport is found. It is concluded that the onset of convective amplification does not suffice as a trigger mechanism for ALE.

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Category:Physics, Fluids & Plasmas

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