Plasma armature formation in high-pressure, high-velocity hydrogen

The use of a two-stage light-gas gun (2SLGG) as a preaccelerator in combination with a railgun is expected to reduce barrel ablation and improve overall performance significantly. To continue acceleration of the projectile, a plasma armature must be formed. Two methods of converting a portion of the fast-moving hydrogen gas into a plasma armature capable of supporting currents exceeding 100 kA are reported. This work is part of STARFIRE, a joint project to develop a hypervelocity railgun. Both fuse and spark discharge techniques were tested with low-velocity single-stage injectors, and a projectile-mounted fuse was tested and a 2SLGG and the HELEOS (hypervelocity experimental launcher for equation of state) railgun. Both aluminum foil and vapor-plated fuses formed plasma armature when vaporized by current provided by a 830-μf capacitor charged to between 1 and 2 kV. Spark discharge armature formation was also successful in the nitrogen injector railgun. It is concluded that the advantages of 2SLGG injection can be realized only by preventing premature plasma formation in front of the projectile while forming an armature behind the projectile after entrance into a railgun