PERFORMANCE-CHARACTERISTICS OF A HIGH-VELOCITY, 25MM RAILGUN

This paper documents a series of tests in a 4.8 m long, 25 mm square b ore railgun that characterize plasma armature behavior in a hyperveloc ity regime. Projectile masses ranging from 15 to 23 grams were acceler ated to velocities of 2.5 to 5.6 km/s. A linear decrease in momentum t ransfer efficiency with velocity was observed. This performance degrad ation was greater than predicted, and may be caused by the failure of the plasma armature to remain compact. Secondary arcs were noted when copper alloy rails were used, and an expanding primary are was observe d when molybdenum rails were used. In an attempt to circumvent armatur e expansion, the railgun configuration was modified to include a muzzl e shunt resistor; this modification is a type of augmentation, such th at the ratio of armature magnetic force to armature current is increas ed. Muzzle shunt augmentation (MSA) had little effect on the plasma ar mature's behavior. Measurements of the momentum transfer efficiency du ring acceleration show a slight but significant increase in efficiency of the MSA configuration over the simple breech-fed configuration. Th is paper describes an effort to quantify the various loss mechanisms b y comparing experimental performance (velocity) to model predictions.