Thermal Analysis of a Series Thyristor Module Prototype for Realizing Repetitive Operation of a Compact Torus Injector

Pulse thyristors are extensively utilized in pulsed plasma discharge applications. In this study, a pulse switch prototype is built using two parallel valve groups, each consisting of seven series-connected thyristors. Each thyristor is equipped with an anti-parallel protection diode, a static voltage-sharing resistor, and an RCD (resistor-capacitor-diode) dynamic voltage-sharing circuit. The prototype withstands 24 kV, delivers 150 kA peak current, operates at 10 Hz, and can run continuously for 1 s. Thermal analysis is essential under narrow-pulse high-current conditions to avoid failure from localized overheating. By investigating the expansion process of the conduction zone during thyristor turn-on, a single-thyristor turn-on model and a finite-element model of the multi-layer series thyristor module are established to analyze transient temperature distributions. Results show a non-uniform temperature profile across the silicon wafer, with the hottest zone near the gate ring. During repetitive pulses, the silicon temperature fluctuates rapidly, while the copper base heats up gradually. At a spreading speed of 30 m/s, the gate terminal temperature rises about 38 °C—within safe limits for now, but projected to exceed them under future operating conditions. Thus, improved thermal management will be critical in further development.