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

Abstract

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.