Role of Stable Modes in the ITG-Driven Instability in a Mode-Coupled System

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Kinetic damping in linear gyrokinetic (GK) Vlasov simulations is found to exhibit a bifurcation at the collisionality βc = β*c , above which, i.e. βc >β*c , the damping is represented by a Landau eigenmode in velocity space, while below which, i.e. βc < β*c , by the phase mixing of a finite number of marginally stable, discretized Case-van Kampen eigenmodes. The latter causes a recurrence that restricts the damping and then the energy transfer from wave to particles within a finite recurrence time. In order to address whether the stabilization effect due to such stable damped modes on unstable modes via mode coupling can be evaluated in long timescale GK simulations, we introduced a triad model consisting of stable and unstable modes incorporated with a tertiary vortex flow. We identified β*c numerically and found that the stabilization effect works properly beyond the recurrence time even in the phase mixing regime across βc = β*c .
社団法人プラズマ・核融合学会の論文