Performance characteristics of a high velocity, 25 mm railgun

This paper documents a series of tests in a 4.8 m long, 25 mm square bore railgun that characterize plasma armature behavior in a hypervelocity regime. Projectile masses ranging from 15 to 23 grams were accelerated to velocities of 2.5 to 5.6 km/s. A linear decrease in momentum transfer efficiency with velocity was observed. This performance degradation 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 arc was observed when molybdenum rails were used. In an attempt to circumvent armature expansion, the railgun configuration was modified to include a muzzle shunt resistor; this modification is a type of augmentation, such that the ratio of armature magnetic force to armature current is increased. Muzzle shunt augmentation (MSA) had little effect on the plasma armature´s behavior. Measurements of the momentum transfer efficiency during acceleration show a slight but significant increase in efficiency of the MSA configuration over the simple breech-fed configuration. This paper describes an effort to quantify the various loss mechanisms by comparing experimental performance (velocity) to model predictions.<>