Development of a fuseless small-bore railgun for injection of high-speed hydrogen pellets into magnetically confined plasmas

A fuseless, small-bore, two-stage railgun system particularly suited to accelerating frozen hydrogen pellets for fueling magnetically confined plasmas is described. This railgun system is a two-stage accelerator, with the first stage consisting of a combination of a hydrogen pellet generator and a gas gun, while the second stage is a railgun. It is a fuseless railgun in that the plasma armature is formed by electrically breaking down the propellant gas immediately behind the pellet. It has a bore size in the range of a few millimeters in diameter. Results are presented on hydrogen pellet acceleration, indicating that it is feasible to use a railgun to accelerate hydrogen pellets to high velocities; however, to achieve the highest hydrogen pellet velocity, one must reduce gun wall ablation (to minimize inertial and viscous drag) and deterioration of pellet integrity. Using a prototype system, hydrogen pellet velocities exceeding 2.8 km/s were achieved on a 2 m-long railgun for a cylindrical pellet of 3.2 mm diameter and 4 mm length