Hybrid simulation of instabilities driven by multiple fast ion species in the Large Helical Device

In the fusion devices, there are multiple fast ion species such as fusion product α-particles and fast deuterons. These fast ions may induce instabilities such as Alfvén Eigenmodes (AEs) which enhance fast ion transport. The study of fast ion driven instabilities is one of the important topics.

To clarify the relationship between AEs and fast ion transport in the multiple fast ion species plasma, experiments with the combined injection of hydrogen and deuterium beams were conducted in the Large Helical Device. The AE bursts caused by the fast protons and fast deuterons were observed in the experiments [1].

In the plasma with multiple fast ion species, a complex synergetic effect of multiple fast ion species may arise on the AEs and fast ion transport, because the interaction with the AEs may differ for different species. For example, one ion species may drive an AE while another species may stabilize it. The stabilizing ion species may be transported by the AE driven by another species.

Computer simulation is a useful tool for investigating the synergetic effect. In this study, simulations of the experiments with the fast protons and fast deuterons are performed using a hybrid simulation code for nonlinear MHD and energetic particle dynamics, MEGA code, where NBI, collisions, and fast ion losses are taken into account. The instabilities induced by each fast ion species will be identified and the synergetic effect of multiple fast ion species will be investigated.

[1] S. Kamio, et al, Plasma Fusion Res., 16, 2402044(2021).