Plasma start-up design for initial discharges in HL-2M

Description of the coil current waveform design method based on the circuit equation for the plasma-conductor-power system. Evolution of eddy currents during the discharge and its effect on the field null configuration. For the first plasma of a new tokomak, the simply and efficiently compensation method for stray magnetic fields of eddy currents, and the practical design method for the self-consistent discharge waveform. HL-2M is a new medium-sized copper-conductor tokamak currently under final construction. Taking into account potential uncertainties in the engineering construction and to resolve design anomalies associated with new machine startup, high loop voltages (>10 V) without ECRH-assisted startup will be one of the important scenarios for the first plasmas in HL-2M. A basic field null configuration is obtained, that satisfies the initial discharge breakdown and the discharge evolution specifications, utilizing the CS, PF6 and PF8 coils of HL-2M. High loop voltage induces large stray magnetic field due to wall eddy currents in the vacuum vessel. Two schemes for compensating the stray field are investigated, using the PF8 coils. One scheme assumes the compensating current IPF8 being proportional to the wall eddy current, and the other scheme assumes fixed IPF8. With two schemes, self-consistent discharge waveforms are designed for the limiter configuration, by solving circuit equations for the plasma-conductor-power system. With the compensating current IPF8 fixed at a value between −150 A and −200 A, a good field null configuration is obtained. Evolution of the equilibrium configuration is further evaluated by the EFIT code, confirming self-consistency of the discharge waveform.