Influence Analysis of Discharge Branch on the Reliability of Quench Protection System in Large Fusion Device

Large fusion device uses high current magnetic field in the superconducting coil to generate high intensity magnetic field, thus constraining the high-temperature plasma to conduct fusion experiments. Therefore, the reliability of quench protection system, especially DC protection switch, is very important for the protection of the superconducting coil. However, the reliability of the DC protection switch is affected by many factors, including the action time, the speed of arc extinguishing, the current drop rate of the switch and the voltage rise rate around zero-crossing point. In the literature on quench protection system design of fusion devices such as ITER (International Thermonuclear Experimental Reactor), the influence of circuit stray parameters on switch reliability is rarely described, and the influence of discharge circuit to quench protection system is less. However, the larger stray parameters of discharge circuit will greatly reduce the operational reliability of the DC protection switch and even lead to failure and damage of the switch.
In this paper, the quench protection system of CFETR (China Fusion Engineering Test Reactor) is presented as an example. Firstly, the influence of the parameters of the discharge branch on the reliability of the quench protection system is analyzed. Then the influence factors and the influence trend are analyzed by theoretical calculation, and the correctness of the theoretical analysis of the current and voltage of each branch is carried out in a set of simulations. The simulation results show that when the stray inductance of discharge branch is large, the parameters of each branch will be greatly impacted, which directly affects the reliability quench protection system in large fusion device.
* This work was supported by a grant from University of Science and Technology of China and the Plasma Laboratory in City University of Hong Kong.