Energetic-particle-driven MHD instability in Heliotron J adjusted via key plasma parameter

A large number of energetic particles (EPs) are generated in 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 degrades the plasma confinement and heating efficiency, but also results in excessive heat loads and damage to plasma-facing components. In this work, the influences 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 mechanism 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 work, 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 are analyzed in depth, revealing the evolutions of AEs and EPMs in the Heliotron J device under typical heating conditions. This study quantitatively reveals the driving and suppressing mechanisms of EP-driven instabilities by the electron density (<i>n</i><sub>e</sub>), the electron temperature (<i>T</i><sub>e</sub>), and the energetic/thermal particle specific pressure (<i>β</i><sub>f</sub>/<i>β</i><sub>th</sub>) in Heliotron J device, under the conditions of different electron cyclotron resonance heating (ECH) and neutral beam injection (NBI). The results show that different characteristics are obtained under the different magnetic field geometry conditions. The results show 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 an inhibitory effect of 20%–50% 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.