Resonant and non-resonant internal kink modes excited by the energetic electrons on HL-2A tokamak

[摘要] Strong resonant and non-resonant internal kink modes (abbreviated as RKs and NRKs, respectively), which are also called resonant and non-resonant fishbones, are observed on HL-2A tokamak with high-power ECRH  +  ECCD⁻ (or ECRH) and ECRH  +  ECCD⁺, respectively. ('Resonant' derives from the existence ofq   =  1 surface (the resonant surface), and 'non-resonant' originates from the absence ofq   =  1 surface (1$ " align="top">{{q}_{ext{min}}}>1 ). ECCD⁺ and ECCD⁻ mean the driving direction of energetic electrons is the same and opposite to plasma current, respectively.) RK has features of periodic strong bursting amplitude and rapid chirping-down frequency, but NRK usually has the saturated amplitude, slow changed or constant frequency and long-lasting time. The NRK excited by energetic electrons is found for the first time. The reversedq -profiles are formed, andq _min decreases during plasma current ramp-up. The value ofq _min is slightly smaller and a bit bigger than unity for RK and NRK conditions, respectively. The internal kink mode (IKM) structures of RKs and NRKs are confirmed by the ECEI system. Although there are different current drive directions of ECCD for excitation of RK and NRK, they all propagate in electron diamagnetic directions in poloidal. The radial mode structures, frequency and growth rate for IKMs are obtained by solving the dispersion relationship. The NRK is stable whenq _min is larger than a certain value, and with the decreasingq _min the frequency drops, but the growth rate almost keeps constant when 1$ " align="top">{{q}_{ext{min}}}>1 . This result is in agreement with experimental observation. Studying IKMs excited by energetic electrons can provide important experimental experiences for ITER, because the NRKs may be excited by high-power non-inductive drive of ECCD or ECRH in the operation of hybrid scenarios.

[关键词] energetic electron;internal kink mode;q-profile