Optimization of Rail-Armature Coupling for the Enhanced Electromagnetic Pellet Injection in J-TEXT Tokamak

Abstract

Major disruption poses a significant challenge to the safe operation of tokamaks, so disruption mitigation is a key problem to be solved in tokamak. Currently, the fundamental strategy of disruption mitigation involves actively injecting significant quantities of impurity gas or solids (such as neon, argon, deuterium, etc.) to generate sufficient radiation power for dissipating the plasma’s energy. The most commonly used disruption mitigation devices now are massive gas injection (MGI) and shattered pellet injection (SPI). However, The impurity injection rate is low, resulting in shallow deposits in the tokamak. Electromagnetic pellet injection (EMPI) is a relatively new generation of disruption mitigation system developed in J-TEXT Tokamak. The system is based on the electromagnetic rail run concept. It uses electromagnetic force to launch the armature with an impurity pellet. The EMPI has been tested several times and the speed of the pellet has broken through the speed of sound, far exceeding the launch speed of the traditional disruption mitigation system. This means impurity is deposited at a deeper location. However, the rail length of EMPI is too long and the rail ablation is serious, so it is a challenging problem to satisfy the tokamak installation space requirements. Therefore, based on the EMPI, an enhanced EMPI is designed, which increases the electromagnetic force by increasing the magnetic field intensity within the bore. This enables the rail length to be decreased to meet the specified condition. Building upon this foundation, various armature-rail coupling structures have been designed. These structures are subjected to COMSOL finite element simulation to determine which rail-armature interface exhibits minimal ablation, superior electrical contact, and maximal armature launch velocity. Subsequently, the optimal rail-armature coupling scheme is validated through an experimentation test.