Transition from fishbone mode toβ-induced Alfvén eigenmode on HL-2A tokamak

In the presence of energetic particles(EPs)from auxiliary heating and burning plasmas,fishbone instability and Alfvén modes can be excited and their transition can take place in certain overlapping regimes.Using the hybrid kinetic-magnetohydrodynamic model in the NIMROD code,we have identified such a transition between the fishbone instability and theβ-induced Alfvén eigenmode(BAE)for the NBI heated plasmas on HL-2 A.When the safety factor at magnetic axis is well below one,typical kink-fishbone transition occurs as the EP fraction increases.When q0 is raised to approaching one,the fishbone mode is replaced with BAE for sufficient amount of EPs.When q0 is slightly above one,the toroidicity-induced Alfvén eigenmode dominates at lower EP pressure,whereas BAE dominates at higher EP pressure.

Fishbone Mode Excited by Deeply Trapped Energetic Beam Ions in EAST

This paper describes the fishbone mode phenomena during the injection of highpower neutral beams in EAST（Experimental Advanced Superconducting Tokamak）.The features of the fishbone mode are presented.The change in frequency of the mode during a fishbone burst is from 1 kHz to 6 kHz.The nonlinear behavior of the fishbone mode is analyzed by using a prey-predator model,which is consistent with the experimental results.This model indicates that the periodic oscillations of the fishbone mode always occur near the critical value of fast ion beta.Furthermore,the neutral beam analysis for the discharge is done by using the NUBEAM module of the TRANSP code.According to the numerical simulation results and theoretical calculation,it can be concluded that the fishbone mode is driven by the deeply trapped energetic beam ions in EAST.

Frequency multiplication with toroidal mode number of kink/fishbone modes on a static HL-2A-like tokamak

In the presence of energetic particles(EPs),the long-lived mode(LLM) frequency multiplication with n=1,2,3,or higher is often observed on HL-2A,where n is the toroidal mode number.Hybrid kinetic-MHD model simulations of the energetic particle(EP) driven kink/fishbone modes on a static HL-2A-like tokamak using NIMROD code find that when the background plasma pressure is relatively high,and the EP pressure and the beam energy are relatively low,the mode frequency increases almost linearly with EP pressure,and the frequency is proportional to n(’frequency multiplication’),even in the absence of any equilibrium plasma rotation.In addition,the frequency multiplication persists as the safety factor at the magnetic axis q_(0)varies.In the absence of EPs,the growth rate of the 1/1 mode is the largest;however,as the EP pressure increases,the growth rate of 2/2 modes or 3/3 modes becomes dominant,suggesting that higher-n modes are more vulnerable to EPs.These results may shed light on the understanding of the toroidal mode number dependence of kink/fishbone modes in the advanced scenarios of tokamaks with weak or reversed central magnetic shear.