On Kink Modes and Low-n Kink β Limits in HL-2A Sawtooth Discharges

Kink mode is one of the most important macroinstabilities in sawtooth discharge. In this article, the nature of kink modes was investigated through a combination of HL-2A experiments and simulations. Multiplen (toroidal mode number) kink branches were found in HL-2A sawtooth discharges. The distinct roles of differentn-kink modes in plasma instability were identified. Then= 1 mode is identified as the dominant kink mode. The mode structure shrinks toward the center with an increase innvalue. The mode linear growth rate is not necessarily related to whether the mode dominates plasma. The weakening effect of the shorter wavelength and its higher internal localization partially offset the advantage of the highernmode in the global plasma instability. In practice, multiplen-kink branches tend to be stable ifn= 1 mode is stable. Among the low-nmodes, the stability limits forn1 modes would not be lower thann= 1 mode at q ₀= 1. 05and its adjacent areas, and the stability limits ofn= 1 and2kink modes decrease with q ₀and exhibit some linear relationships if a normally parabolic current density profile is considered, which hints for the determination of the operational for HL-2A sawtooth discharges.