Dependence of Energy Flow on the Translation Velocity in Collisional Merging of Field-Reversed Configuration

The dependence of energy flow on translation velocity in the collisional merging process of field-reversed configurations (FRCs) is evaluated in the FAT-CM device at Nihon University. Two FRC-like plasmoids formed by field-reversed theta-pinch are translated directly towards each other and collide at super-sonic/Alfvénic velocity. These plasmoids eventually become one FRC by the collisional merging. Assuming that an FRC has little axial velocity after merging, the kinetic energy of initial plasmoids is released to the outside of the confinement or regenerated into internal energy. The energy regeneration in the collisional merging process was experimentally observed [1]. In this work, the regeneration from kinetic energy into internal energy in the collisional merging of initial plasmoids is evaluated by comparing the cases of high and low translation velocity. The initial plasmoids are accelerated due to the magnetic pressure gradient provided by the conical theta-pinch coils. Current density is controlled by changing the pinch coil geometry to a shorter length, then the high magnetic pressure is generated in the formation sections on both ends of the device and the kinetic energy of initial plasmoids is increased.

[1] D. Kobayashi et al., Plasma Fusion Res. 16, 2402050 (2021).