Gyrokinetic simulations of the influence of electron cyclotron current drive on tearing mode instabilities in tokamaks

TL;DR

This study uses gyrokinetic simulations to analyze how electron cyclotron current drive and ion kinetics influence tearing mode instabilities in tokamaks, demonstrating stabilization effects and the importance of ion temperature.

Contribution

It presents the first detailed gyrokinetic simulation of electron cyclotron current drive effects on tearing modes in HL-2A and DIII-D tokamaks, including ion kinetic effects.

Findings

Complete stabilization of tearing modes in HL-2A with 1MW 68GHz X2-mode.

Partial stabilization in DIII-D with 1MW 110GHz X2-mode due to lower power.

Ion presence reduces island width and growth rate, especially at higher ion temperatures.

Abstract

A gyrokinetic simulation of the influence of electron cyclotron current drive and ion kinetic effect on the m/n=2/1 tearing mode (TM) instabilities is presented in HL-2A and DIII-D tokamak configurations. The TM evolution is calculated with a finite mass electron model and the rf current source is obtained by ray-tracing and the Fokker-Planck method. The TMs are found to be perfectly stabilized by a continuous 1MW 68GHz X2-mode in HL-2A tokamak, while instabilities in the DIII-D discharge (with lower value of CR=I_{rf}/I_{0}, where Irf is the wave driven current and I0 is the equilibrium plasma current) are only partially stabilized with the 1MW 110GHz X2-mode due to inadequate power input. The result also indicates that a helicon current drive is more efficient than a continuous ECCD. Analysis of the GTC simulation reveals, both in HL-2A and DIII-D, that the presence of ions can reduce the island width as well as the growth rate. Furthermore, the kinetic effect of thermal ions on TM is found to be more pronounced with higher ion temperature.