Investigation of field null for HL-2M tokamak start-up

In this paper, we presented a dynamic modeling of the inductive plasma start-up using an ohmic solenoid coil (CS) and some shaping coils (PF) for stray field compensation for the HL-2M tokamak including three start-up stages: the initial magnetization, the flux swing and the breakdown. A static field null calculation was performed for the initial magnetization stage and the static results was the base of flux swing stage calculation. The initial flux is enough for plasma current ramp-up. For the flux swing stage, A time-dependent calculation using finite element method was involved with vacuum vessel eddy current induced by coils current ramp-down. At the end of flux swing stage, the current waveform of PF coils were precisely optimized for compensating the stray field to generate a field null through the dynamic compensation. At the same time, the toroidal electric field ramped up to 0.6 V/m for breakdown. For breakdown stage, toroidal electric field and sufficient size of the E_t·B_t/B_p = 1 kV/m contour was sustained for several milliseconds for successful breakdown. And then, the plasma current was assumed to ramped up linearly at 1MA/s for several decade milliseconds with the vertical field applied.