In the second half of 2022, Startorus completed assembling the main body of SUNIST-2, a spherical tokamak. Its work on magnet-supporting pulsed power supplies also pressed forward smoothly. Such progress has prepared Startorus for verifying the viability of its fusion proposals and laid a solid foundation for the company to level the plasma performance of its device up to that of the world’s leading devices of the same size in the next stage. 

Generally speaking, tokamaks employ many magnets for the toroidal field (TF), poloidal field (PF), and central solenoid (CS) to both generate and heat plasma and sustain confinement and equilibrium. Although these magnets for different purposes require different power supplies, all of them should be equipped with an output current capacity ranging between 10kA and 100kA to produce intense-enough magnetic fields within a rather large space. They are all highly challenging pulsed power supplies. 

Top-left: The Power Supply System of Startorus’s Fusion Device

Bottom-right: Structure of Coils in Tokamaks      

Source: Startorus Fusion 

To produce an on-axis toroidal magnetic field of 1 T in a spherical tokamak, the power supply responsible for the field must be able to output a current above 100kA within a time span measured by second. Given the operation features of the toroidal field, Startorus adopts a modular design, where the energy storage unit, inverter and control circuit are integrated into a kA-level power supply module in the form of stacked arrays, to ensure the 100kA current output. With built-in state monitoring systems and complete protective measures, the power supply performs desirably in adjusting currents and boasts strong flexibility. Based on this module, other power supplies of various topological structures and current levels can be established quickly. At present, all modules of the power supply have been placed in respective positions, generating a stable 44kA current requisite for initiating discharging of the spherical tokamak at the preliminary stage.

Given that power supplies charging the poloidal magnets are expected to make quick and accurate feedback adjustments, Startorus resorts to multilevel energy storage and switch topology. As PF power supplies are large in number, a compact design is preferred, where an H-bridge comprised of ten IGBT high current switches is integrated with energy storage units. While occupying little space to the largest possible extent, this arrangement reduces stray inductance significantly and improves the reliability of the power supplies. At present, the power supplies maintain stable operation at the rated current level of 10kA.

To give full play to the magnetic flux of the central solenoid, the CS power supply is required to provide a bidirectional current of ±20kA. The team ingeniously designs the CS power supply by replicating many modules of the PF power supplies because of the similarities between them. At present, the CS power supply has passed the test and has been operating stably at a level of ±22kA.

With the total power capacity topping 50MW, these pulsed power supplies have paved the way for Startorus to verify its technical proposals. More importantly, they embody the creativity, engineering capability and executive force of the team and vividly mirror Startorus’s work style of dauntless attempt and shared responsibility.