Finite ion orbit width effect on the neoclassical tearing mode threshold in a tokamak plasma

Nuclear Fushion

article

K. Imada¹  H.R. Wilson¹  J.W. Connor²  A.V. Dudkovskaia¹  P. Hill¹ 

[1] York Plasma Institute, Department of Physics, University of York;CCFE, Culham Science Centre

关键词: tearing mode;    magnetic island;    MHD;    threshold;    NTM;   

DOI  :  10.1088/1741-4326/ab00ba

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

A new drift kinetic theory for the response of ions to small magnetic islands in toroidal plasma is presented. Islands whose widthwis comparable to the ion poloidal Larmor radius are considered, expanding the ion response solution in terms of, whereris the minor radius. In this limit, the ion distribution can be represented as a function of toroidal canonical momentum,. With effects of grad- Band curvature drifts taken into account, the ion distribution function is a constant on a 'drift island' structure, which is identical to the magnetic island but radially shifted by. The distribution is then flattened across the drift island, rather than the magnetic island. For small islands, the pressure gradient is maintained across the magnetic island, suppressing the bootstrap current drive for the neoclassical tearing mode (NTM) growth. As, the ions are largely unperturbed. However, the electrons respond to the electrostatic potential required for quasi-neutrality and this provides a stabilizing contribution to the NTM evolution. This gives a new physical understanding of the NTM threshold mechanism, with implications for the design of NTM control systems for future tokamaks such as ITER.

【 授权许可】

Unknown