Plasma dynamics of an arc-driven, electromagnetic, projectile accelerator

Abstract

A model is analyzed to study the electromagnetic acceleration of projectiles using a device known as the rail gun. Current is conducted between the rails by a plasma arc which drives the projectile. The analysis includes determining the electromagnetic fields within the gun and solving the fluid-mechanical equations of the plasma under the assumption that the flow parameters are steady in a frame that accelerates with the arc. Specifically, a set of coupled equations is derived which, when solved, yields the properties of the arc and the acceleration of the projectile. A limiting-case analytic solution to the equations is found, and an iterative technique is employed to solve the equations numerically in the more general case. The results of the calculation are applied to analyze the arc in an experiment recently carried out by Rashleigh and Marshall. Some approximate scaling relations, which indicate how the properties of the arc vary with the dimensions of the rail gun, the mass of the projectile, the mass of the arc, and the accelerating current, are then derived. The results of the calculation are compared with those of others and some suggestions for future investigations are given.