Magnet Operation Strategies for Achieving Mega-Ampere Plasma in the HL-2M Tokamak

HL-2M, a medium-sized tokamak equipped with copper conductors, features a magnetic system comprising a toroidal field (TF) magnet and a poloidal field (PF) magnet. The TF magnet, composed of 20 D-shaped coils, is designed to generate a magnetic field of 3 T at the plasma center. The PF magnet system includes a central solenoid (CS) with two sets of coils and eight pairs of independent PF coils, capable of sustaining the plasma with a flux swing in excess of 14 Vs. Prior to entering the mega-ampere plasma operation phase, both TF and PF magnets underwent routine pre-operation inspections. Notably, the TF magnet was pre-stressed using a synchronous hydraulic system to counterbalance the electromagnetic forces from the PF coils, the plasma, and the TF coils themselves. During operational phases, the magnet system was closely monitored by a dedicated machine safety control system that measured electrical parameters such as terminal voltages, coil currents, and grounding currents. To mitigate the risk of mechanical overloading, diligent regulation of the interaction between the thermal dynamic loads borne by the TF coils and the force exerted by the hydraulic system was implemented. Three-axis accelerometers were installed on the TF coils to measure local forces directly. Through composite detection methods, the TF coil magnetic field achieved 1.5 T, the CS coil current reached 100 kA, and a plasma current of 1.15 MA was successfully sustained. The preparation and implementation of a safety control system for magnet operation, with particular attention to mechanical load control of the TF magnet, are crucial for the successful mega-ampere operation of HL-2M.