Global Simulation of Reactive Species Generation in Atmospheric Argon/Oxygen Plasma with Pulsed Power Source.

Abstract

The boundary of high-temperature plasma confined by a toroidal magnetic field structure (a.k.a. tokamak) often shows quasi-periodic relaxation oscillations between high and low energy states [1]. On the KSTAR tokamak, the relaxation oscillation consists of a quasi-steady state characterized by field-aligned filamentary eigenmodes, an abrupt phase transition into non-modal filamentary structure [2], and its rapid burst leading to a large loss of heat and particle. We propose a phenomenological yet very general model including the effects of time-varying perpendicular flow shear, turbulent transport, and pressure profile. Our model shows that the amplitude and shear of the flow across the plasma boundary are the key parameters determining the nonlinear oscillation. Numerical solutions for a range of the flow amplitude and shear indicate that a steadystate exists only for weak flow. This result suggest that (1) the abrupt transition from the quasi-steady eigenmode to the non-modal state is due to an increase of the flow, and (2) the suppression of filament burst by external magnetic perturbations [3] may be due to the reduction of the flow.