Analysis and improvement of θ-pinch system for field-reversed configuration formation

Field-reversed theta pinch is employed to generate the initial Field-Reversed Configuration (FRC) plasma in the HUST-FRC fusion experimental device. The operational stability of the θ-pinch system is crucial for the formation of high-performance and reproducible FRCs. Nevertheless, during discharge experiments, recurrent self-triggering and conduction faults of the hydrogen thyratron switches have been detected, which undermines the reliability of FRC formation. This study offers a comprehensive analysis of these discharge faults and proposes an improved scheme for the θ-pinch system. Through simulation and experimental tests, the root cause of the faults is determined to be the complex coupling interference among the four parallel discharge branches (Bias, Pre-ionization, Main, and Crowbar). To address these faults, an improved θ-pinch system is proposed, characterized by a newly developed high-voltage pulsed power supply topology and a double-layer θ-pinch coil structure. Repetitive discharge tests have shown that the improved system attains an average normal discharge coil ratio of 97.4%, thereby significantly enhancing the stability of the θ-pinch system. The proposed improvements meet the stringent operational requirements for reliable formation of FRC plasma.