April 15-17

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Author: Min-Gu Yoo
Requested Type: Poster
Submitted: 2019-02-22 16:00:18

Co-authors: W.X. Wang, E. Startsev, C.H. Ma, W.W. Lee, S. Ethier

Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Road
Princeton, New Jersey   08540
United States

Abstract Text:
The physical mechanism of the thermal quench, a sudden collapse of the plasma temperature, has not been clearly revealed yet. A global nonlinear gyrokinetic simulation code GTS is recently upgraded to study the electrostatic plasma response to the magnetic islands which is essential to understand the thermal quench physics. As the first step to understand the magnetic island effects on the plasma transports especially for the turbulence physics, we study a static single-harmonic magnetic island case with the GTS code. We applied a static magnetic perturbation of (m,n)=(3,2) mode on the cyclone base equilibrium in which the ITG turbulence dominates. We investigated a temporal evolution of the plasma fluctuation from the initial linear ITG growth stage to the nonlinear saturated phase in the presence of the magnetic island at the resonant surface (q=1.5). At the initial stage, before ITG modes grow, the electron temperature profile is rapidly flattened inside the magnetic island due to a fast electron streaming along the perturbed magnetic fields. As electrostatic plasma potential rises due to the ITG turbulence, the ExB transports come into play an essential role in the nonlinear saturated stage. It was observed that the size of the magnetic island determines the degree of the temperature flattening and the plasma transport behavior around the island. A small island could not influence the plasma transports, and the ITG turbulence penetrates across the magnetic island. On the other hand, a large island could build up the high electrostatic potential correlated with the island structure, so it induces strong ExB flows around the magnetic island. The strong ExB flow and its high shearing rate strongly influence the plasma transport so that the typical ITG turbulence modes could be mitigated or suppressed at the magnetic island region.

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