Revisiting the performance of a plasma armature railgun

Abstract

Some experimental results obtained from a series of firings using a small-bore two-stage plasma armature railgun are presented which contradict assumptions employed in more recent attempts to model plasma armatures in railgun firings. By introducing the current - time behaviour into the equation of motion for the plasma - projectile system, an expression for a limiting exit velocity is obtained. This general expression is dependent upon the rail inductance per unit length when no anomalous effects occur in a firing. Since current diffusion is not significant close to the plasma - projectile system during a firing, the current distribution can be assumed to be in the form of thin sheets along the inner rail surfaces, thereby enabling the rail inductance per unit length to be evaluated. Different values for the height of the current sheets are then used to evaluate the rail inductance per unit length. When introduced into the expression for the limiting exit velocity, all yield significantly higher exit velocities than those recorded in railgun firings. These results explain the relatively poor performance of a railgun without the need to incorporate relativistic effects as in recent work.