Abstract
Multiple quasicoherent electromagnetic modes with steady-state frequency and different nature and location were observed in the COMPASS tokamak (R = 0.56 m, = 0.2 m) at B-t = 1.14T with Co-NBI (P-NBI = 0.2-0.5 MW, E-b = 32 keV) at frequencies 5 kHz < f < 250 kHz. Modes were observed in both low and high confinement (L- and H-modes) plasmas.
Lower frequency modes with f < 50 kHz were identified as low m tearing and kink MHD modes, while higher frequency modes with 50 kHz < f < 250 kHz were considered as having Alfvenic nature. Unexpectedly, such modes were only observed in the H-mode, both in neutral beam injector-assisted and Ohmic, so the mode driving force is not yet clear.
Using the linear MHD code KINX, we initially identified the observed mode with a ballooning structure is as beta induced Alfven eigenmode (BAE) with m, n < 5, while an antiballooning mode is initially identified as toroidal Alfven eigenmode (TAE) with m, n < 9.