托卡马克等离子体中共振磁扰动场放大效应对离子轨道特性的作用

Field amplification effect of resonant magnetic perturbation on ion orbits in tokamak plasma

首先,利用MARS-F程序模拟了HL-2A装置中不同电阻率、环向旋转频率和环向模数条件下等离子体对共振磁扰动(RMP)的线性响应过程,分析了不同情况下共振场放大效应对三维扰动磁场的影响;然后,利用Boris算法追踪了三维场作用下的离子轨道,并详细探究了不同扰动磁场改变离子轨道特性的物理机制.研究发现,考虑等离子体响应后的扰动磁场可增强离子轨道径向展宽,且轨道最大径向展宽随轨道上扰动磁场平均值的增大而增大;同时,离子在通过扰动磁场被强烈放大的区域时轨道径向展宽会显著增加.该物理机制可用于解释RMP缓解边界局域模实验中离子直接损失增加和等离子体径向输运增强现象.

The fast ion transport associated with resonant magnetic perturbation(RMP)contains rich physical spanning single particle motion of fast particle and plasmas response physics with RMP and their interaction.Full numerical simulation considering such physical ingredients should be performed in a long run for clarifying the underlying physical features of the fast ion confinement with RMP.Thus,the appropriate application of RMP is not only to avoid the detrimental effects but also to serve as an actuator to exert targeted control over the energetic particle profile.To achieve this goal,a comprehensive knowledge of the effects of RMP including plasma response on fast ions is necessary.In this work,the plasma response to RMP in HL-2A device is simulated by the MARS-F code under different parameters including finite resistivity,toroidal rotation frequency and toroidal mode number,and the three-dimensional(3D)magnetic field topology considering RMP is obtained.Then,Boris algorithm is used to track the ion orbit under these 3D fields,and the physical mechanism of ion orbit characteristics changed by the perturbed field is explored in detail.It is found that with the increase of finite resistivity,the average value of perturbed magnetic field decreases,and the orbit radial expansion turns smaller.The variation of toroidal rotation frequency can change the distribution of perturbed magnetic field,resulting in different orbit radial expansions for different kinds of orbits.What is more,if the toroidal mode number increases,the amplitude of perturbed magnetic field after response decreases obviously,thus resulting in little effect on orbit radial expansion.In a word,the plasma responded RMP field enhances the orbit radial expansion,and the maximum orbital radial expansion increases with the augment of average value of perturbed magnetic field on the orbit.Meanwhile,the amplitude of orbit expansion increases significantly when the ions pass through the region where the perturbed magnetic field is strongly amplified.This effect can explain the increase of ion prompt loss and enhancement of plasma radial transport in edge localized mode mitigation experiments by RMP.