Influence of circulating fast ions on nonlinear kink-tearing modes in tokamak plasmas

Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University Chengdu, Sichuan 610031, China

^(a) xianquwang@swjtu.edu.cn

Received: 10 May 2016
Accepted: 30 August 2016

Abstract

Nonlinear radial displacement modified by the kinetic effect of circulating fast ions is derived. It is found that circulating fast ions play a crucial role in the nonlinear dynamics of m = 1 kink-tearing modes. For a large fraction of fast ions, resonant fast ions can destabilize the mode by wave-particle interaction and enhance the mode saturation level significantly, meanwhile, fast-ion current has a modification on the mode amplitude depending on the plasma pressure gradient. A relation of mode amplitude to linear growth rate is explored by this model, which is valid to study the effects of circulating or trapped fast particles on the mode. The calculation results for the ITER-like parameters suggest that the kink-tearing mode with a global structure is dominated by the wave-particle interaction rather than the fast-ion current, particularly for the small island in which the fraction of fast ions is ignorable in comparison with the ideal region. The dependence of radial displacement on the mode frequency is discussed for different stabilities of the MHD modes.