Hits:

Indexed by:Journal Papers

Date of Publication:2019-08-01

Journal:NUCLEAR FUSION

Included Journals:SCIE、EI

Volume:59

Issue:8

ISSN No.:0029-5515

Key Words:low-frequency fishbone; passing fast ions; finite orbit width; energetic particle mode; tokamak plasmas

Abstract:Low-frequency fishbone instability driven by passing fast ions via wave-particle resonance omega = omega(phi) - omega(theta) is studied within the framework of energetic particle mode (EPM), where omega(phi) and omega(theta) are toroidal transit frequency and poloidal transit frequency of passing fast ions respectively. The effects of finite orbit width of energetic particles are responsible for the low-frequency fishbone of EPM type. It is found that magnetic shear at the q = 1 radius plays an important role in the instability whereas the effect of background plasma beta is weak. In particular, for the case of co-injection of beam ions, there exists a critical magnetic shear below which the beam ion beta threshold for EPM excitation is very small. For moderate or higher magnetic shear, the beam ion beta threshold is much higher, on order of a few percent. These results are consistent with the observation of the low-frequency fishbone in the HL-2A tokamak.