A versatile power supply system for the central solenoid of the QUEST spherical tokamak

•A versatile power supply system is proposed to start up plasma in both inductive and non-inductive scenario.•Through double flux swing OH, plasma current of 110 kA is achieved with the assist of ECH by the versatile power supply.•Triangle-wave-like oscillation on the CS coil current is shaped, which can generate the plasma current in oscillation. Switching IGBT 1 and 2 ON/OFF, alternate current (AC) coil current is feasible This AC OH are an alternative to steady state tokamak operation for long pulse discharges•A capacitor bank with new ignitron circuit was installed it to assist CHI with fast response. Toroidal current was increased to 170 kA. Here, a versatile power supply system, consisting of two current sources, insulated-gate bipolar transistor stacks, and a capacitor bank, is proposed for application in various operations of the QUEST spherical tokamak. The central solenoid coil in this system can carrying a maximum current and voltage of ±8 kA and ±375 V, respectively. In plasma start-up experiments based on ohmic heating through double flux swing, a plasma current of over 100 kA is stably obtained. Moreover, the feedback control of the thyristor power supply is utilized to control the plasma current, plasma shape, and position. The oscillating central-solenoid current applies a bipolar loop voltage at constant time intervals, and the capacitor bank discharge facilitates a co-axial helicity injection as well as amplifies the toroidal current.