Hybrid-kinetic simulation of synergy between fishbone/sawtooth and tearing mode-induced energetic-ion transport in a tokamak plasma

The resonant interaction between m/n = 2/1 tearing mode (TM) and energetic ions redistributed by m/n = 1/1 fishbone/sawtooth collapse has been observed recently in HL-2A neutral beam injection-heated high-density plasmas, where m is the poloidal mode number and n is the toroidal mode number. This event essentially results from a synergistic effect with a multiple-mode nature. Understanding such experimental phenomena, especially when using high-power auxiliary heating, is crucial for achieving high-performance plasmas with high confinement and high beta N in the prospective thermonuclear fusion reactors. In this work, based on the typical experimental phenomenon of synergy between fishbone/sawtooth and TM on HL-2A, a self-consistent nonlinear hybrid-kinetic simulation is conducted utilizing the experimental parameters and profiles before the occurrence of this synergy as the code M3D-K input. In particular, we focus chiefly on the phase-space transport, loss and redistribution of energetic ions induced by two cases, one with only m/n = 2/1 TM and one with synergy between m/n = 1/1 fishbone/sawtooth and m/n = 2/1 TM. It is found that the synergy of the fishbone/sawtooth and m/n = 2/1 TM on energetic-ion transport, loss and redistribution is important and can dramatically enhance the loss rate of energetic ions compared with the case with only m/n = 2/1 TM. It is due to the fact that such synergy can open up an efficient energetic-ion loss channel which connects the plasma center and edge. The phase space transport and redistribution of energetic ions induced by the two different cases are also respectively analyzed and compared in detail. Because of the overestimation of amplitudes of fishbone/sawtooth and TM in the simulations, the obtained energetic-ion transport level is only limited in the context of the numerical framework. These findings indicate that the synergy triggering the sawtooth collapse may lead to an enhancement of the energetic-ion transport and can help us understand the underlying mechanisms of synergy-induced energetic-ion transport.

Automated summary

The resonant interaction between m/n = 2/1 tearing mode and m/n = 1/1 fishbone/sawtooth collapse has been observed in HL-2A experiments and understanding this phenomenon is crucial for future fusion reactors. In this study, a self-consistent nonlinear hybrid-kinetic simulation is conducted to analyze the transport, loss, and redistribution of energetic ions induced by the synergy between fishbone/sawtooth and tearing mode. The results show that this synergy enhances the loss rate of energetic ions due to the opening of an efficient loss channel connecting the plasma center and edge.