Controllability study of plasma vertical instability in HL-2M

摘要

Plasma vertical instability control is achieved by passive stabilization from induced currents flowing in surrounding structures and by active control using magnetic coils. Both aspects are numerically investigated for the medium-size copper tokamak HL-2 M, presently under construction in China. The double-shell vessel can provide some passive stabilization, with the longest wall penetration time of about 4 ms. We design an out-vessel active control system based on a single null divertor equilibria most demanding for vertical control and the maximum controllable vertical displacement dZmax >= 3.0 cm is required. Robust active control of the vertical instability can be achieved in HL-2 M, by the PF7U and PF7L coils connected in anti-phase and powered by an upgraded power supply with I-max = 4.0 kA, V-max = 2 kV and f = 5 kHz. Safe control is possible for representative plasma configurations with growth rate ranging from 200 s(-1) to 400 s(-1). Efficiency of each PF coil location for VDE control is investigated, PF7U/L is most capable for single null and double null equilibria, but control capability of PF7U/L is not as good as PF2U/L for snowflake divertor plasma, PF7U/L and PF2U/L will be combined together to provide safe control of low beta p 'close nulls' advanced divertor plasma in the future.