Research On The Utilization Of Double Swing Fluxes Of The Ohmic Field In The Sunist Spherical Tokamak

SUNIST is the first and the only spherical tokamak device in China. Thecapacitor banks are used as energy storage systems for SUNIST magnetic coils.Theohmic field is mainly used to generate and maintain the plasma current. The formerohmic field power supply circuit of SUNIST is relatively simple and it dischargedonly by using SCR, and only half of the fluxes were used in this way.The double swing fluxes of the ohmic field must be utilized in order to extendthe flat top of plasma current and improve the quality of plasma equilibrium in theSUNIST spherical tokamak. This requires an upgrade of the power system of theohmic field. In this paper, we introduce an H-bridge bidirectional discharge circuit,which is based on four high-current low-frequency switches composed of multipleparallel IGBTs. The core component of double swing discharge circuit------3kV/10kAclass IGBT switches was developed.We selected suitable IGBT modules first, andthen completed the design of the IGBT snubber circuit and drive circuit design, andused the circular array layout and the cascading busbar technologies to achieve bettercurrent sharing.Finally the successful test was achieved.In addition， both the single-phase and three-phase quasi-constant currentcharging circuit for the energy storage capacitor banks of the upgraded power supplywere investigated,the reasonable parameters of the power supply system (such as thecharge system, energy-released system and control system, etc.) for energy storagecapacitors C1and C2in double swing discharge circuit were determined.In theexisting experimental condition, the H-bridge double swing discharge circuit of3kV/10kA parallel IGBT high-current low-frequency switch was installed and testedsuccessfully, and the preliminary experimental results of double swing dischargecurrent for Ohmic field were achieved. After the upgrade，the double swing current, e.g.,+10kA to-6kA, in the ohmic field coils was obtained. The waveforms of plasmacurrent were also improved obviously when compared with the previous waveforms.It laid a good foundation for subsequent experiments.It’s also the first time that theH-bridge bidirectional discharge circuit of3kV/10kA parallel IGBT high-currentlow-frequency switch was used in the magnetic field coils on the tokamak device inthe domestic.