Influence of Key Plasma Parameters on the Excitation and Damping Effect of EP-driven MHD instability in Heliotron J device

A large number of energetic particles (EPs) are generated during the heating process to obtain the high temperature plasma for fusion research. These EPs can resonantly excite various magnetohydrodynamic (MHD) instabilities, including the Alfvén eigenmodes (AEs) and the energetic particle modes (EPMs). The excitation of such MHD instabilities can lead to significant EP losses, which not only degrade the plasma confinement and heating efficiency, but also result in excessive heat loads and damage to plasma-facing components. In this paper, the influence of key plasma parameters on the excitation and damping effect of EP-driven MHD instabilities in Heliotron J device are investigated for better understanding of the excitation and transport mechanisms of EPs driven MHD in specific device, which is meaningful for achieving stable plasma operation in future fusion devices with different heating methods. In this study, the typical EPs driven MHD instabilities are observed using various diagnostic methods, such as magnetic probes, beam emission spectroscopy (BES), electron cyclotron resonance (ECE) radiometers, and interferometers. Combined with the simulation results from STELLGAP and FAR3D programs, the modulus, radial distribution, and spectral characteristics of different instabilities were deeply analyzed, revealing the evolutions of AEs and EPMs in the Heliotron J device under typical heating conditions. This paper quantitatively reveals the driving and suppressing mechanisms of EP-driven instabilities by the electron density (ne), the electron temperature (Te), and the energetic/thermal particle specific pressure (βf/βth) in Heliotron J device, under different electron cyclotron resonance heating (ECH) and neutral beam injection (NBI) conditions. The results show that different characteristics are obtained under different magnetic field geometry conditions. It is indicated that an increase in electron density can reduce the instability intensity by about 40%-60%, and an increase in the specific pressure of energetic particles can double the modal growth rate, while an increase in the specific pressure of hot particles has a 20%-50% inhibitory effect on the growth rate of the low order modes. These findings are useful for understanding the different effects of ECH and NBI on the EPs driven MHD instabilities, and they are also helpful for achieving stable operation by adjusting the heating system parameters in the stellarator like devices in the future.