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 MHD instabilities usually co-exist and interact with fast particles. It can cause significant fast particle transport and loss, and pose damage to the first wall, leading to discharge quench in tokamak. Therefore, understanding the physical mechanism of fast particle transport caused by MHD instabilities is a crucial but urgently solved physical issue for the steady-state long pulse operation of future reactor-graded devices. Based on the experimental phenomenon of synergy between nonresonant internal kink mode and tearing mode observed on NSTX, a spherical tokamak device, this paper utilizes the global nonlinear hybrid-kinetic simulation code M3D-K to compare the characteristics of fast particle loss, transport and redistribution in the two cases: I) only non-resonant internal kink modes; II) the synergy between the non-resonant internal kink mode and tearing mode. The physical mechanism of fast particle transport, loss and redistribution caused by such synergy is studied. 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 synergy can provide a radial channel for fast particles to mitigate 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.