托卡马克中低频磁流体不稳定性协同作用引起快粒子输运的混合模拟研究

Hybrid numerical simulation on fast particle transport induced by synergistic interaction of low-and medium-frequency magnetohydrodynamic instabilities in tokamak plasma

在托卡马克实验中,通常会有多种磁流体不稳定性同时存在并与快粒子发生相互作用,引起非常显著的快粒子输运和损失,破坏装置第一壁导致放电淬灭.因此,理解磁流体不稳定性引起快粒子输运的物理机制,对未来聚变堆稳态长脉冲运行是亟需解决的重要物理问题.本文基于球形托卡马克装置NSTX上观测到的非共振内扭曲模与撕裂模发生协同相互作用的实验现象,采用全局非线性磁流体-动理学混合模拟程序M3D-K,比较了两种情况下的快粒子损失、输运和再分布的特征,包括情况1:非共振内扭曲模与撕裂模同时存在并且发生协同相互作用,研究了这种协同作用引起快粒子输运的物理机理;情况2:只有非共振内扭曲模存在.研究结果表明,非共振内扭曲模与撕裂模的协同相互作用可以显著提升快粒子损失和输运水平,主要原因是这种协同作用可以提供一种快粒子沿径向从等离子体芯部向等离子体边界运动的通道,从而提升了快粒子输运、损失和再分布水平.这些结果有助于理解未来聚变堆中低频磁流体不稳定性协同作用引起快粒子输运和损失的物理机理,为寻找控制和缓解未来聚变堆中快粒子损失和输运水平的策略提供一定的新思路.

In tokamak experiments,various magnetohydrodynamic(MHD)instabilities usually co-exist and interact with fast particles.It can cause the fast particles to significantly transport and lose,which results in damaging the first wall and quenching discharge in tokamak.Therefore,the understanding of the physical mechanism of fast particle transport caused by MHD instabilities is crucial and this physical problem needs solving urgently for the steady-state long pulse operation of future reactor-graded devices.According to the phenomenon of synergy between non-resonant internal kink mode and tearing mode,observed experimentally on NSTX,a spherical tokamak device,we utilize the global nonlinear hybrid-kinetic simulation code M3D-K to study and compare the characteristics of loss,transport and redistribution of fast particles in the two cases:1)the synergy between the non-resonant internal kink mode and tearing mode and 2)only non-resonant internal kink modes.The physical mechanisms of transport,loss,and redistribution of fast particles caused by such synergy are studied,respectively.The results show that the synergy between the non-resonant internal kink mode and the tearing mode can significantly enhance the loss and transport of fast particles.The main reason is that such a synergy can provide a radial channel for fast particles to migrate from the plasma core to the plasma boundary accompanied with the total stochasticity of the magnetic topology.These results can help understand the physical mechanism of the transport and loss of fast particles caused by the synergy of low-frequency MHD instabilities in future fusion reactors,and provide some new ideas for finding strategies to control and mitigate the loss and transport level of fast particles in future fusion reactors.