Study of a transaugmented two-stage small circular-bore railgun for injection of hypervelocity hydrogen pellets as a fusion reactor refueling mechanism

Injection of hypervelocity hydrogen pellets has become widely accepted as the most effective means of refueling magnetically confined fusion reactors. Pellet velocities on the order of 10 km/s are desired and hydrogen pellet erosion during acceleration must be minimized. It is important to maintain uniform bore surfaces during repetitive shots, implying that, if a railgun is to be used to accelerate the pellets, damage to the sidewalls and rails of the railgun due to local heating must be limited. In order to reduce the amount of power dissipated within the bore and increase the propulsive force generated by the plasma-arc armature while minimizing losses due to pellet, rail, and sidewall ablation, we have employed a magnetic field transaugmentation mechanism consisting of a two-turn pulsed electromagnet. The two-stage gun consists of a light-gas gun which accelerates a 4- to 5-mg pellet to a speed around 1.2 km/s and injects it into the plasma-arc armature railgun. Currently, we have achieved a final output velocity for a hydrogen pellet of 2.11 km/s with a time-averaged acceleration of 4850 km/s² using a 58-cm railgun pulsed with a peak rail current of 9.2 kA and 28.0 kA of transaugmentation current. This paper will present a description of our hydrogen-pellet-injector railgun system, a discussion of the data on hydrogen pellet acceleration, and projections for future systems