Study of ideal magnetohydrodynamic operational β limit of the HL-2A tokamak

The maximum achievable β limited by external kink modes in HL-2A tokamak plasmas was studied, and the ideal magnetohydrodynamic (MHD) operational β limit of the device was predicted theoretically based on basic plasma parameters and magnetic measured data from conventional sawtooth discharge experiments. It was found that the achievable maximum β is limited by n = 1 kink because the β limit imposed by n = 2 mode is more relaxed than the former. The comprehensive ideal MHD operational β limit of the HL-2A device was determined for the first time as β_N^c = 2.0-2.6. The precise result of β limit depends mainly on the device parameters and is modified for different types of discharges. The operational β limit of the HL-2A limiter plasma was determined to be β_N^c = 2.0. The stability of the kink mode in the divertor plasma was better than that in the limiter plasma under a similar parameter system, and its operational β limit was recognized as β_N^c = 2.6. The β limit predicted in this study is the ideal operating standard for HL-2A sawtooth discharges, which can be achieved experimentally under enhanced heating and current drive methods such as neutral beam injection (NBI) heating and low hybrid current drive (LHCD). (author)