Investigation of techniques to increase armature transition velocity

Abstract

The cause of armature contact transition in railguns arises from the velocity skin current effect. Connected with this event is the evaporation of thin layer of the armature contact surface in a high evaporation leading to an increased voltage drop interface between the armature and the rail and this is followed by arc ignition. Earlier, we showed that the transition velocity depends very weakly on the current and its period in the railgun. In this work we examine the influence on armature transition velocity from other railgun parameters: inductance gradient, mass and dimensions of the armature, and the choice of the armature and rail materials. It has been postulated that a method of increasing the armature transition velocity involves the use of a graphite layer on metallic rails. The experiment carried out by us on the acceleration of the aluminium armature with mass 2.6 g in the nonarc regime up to the velocity 4.6 km/s in a railgun with the copper-graphite rails confirms these expectations. In this work we have compared calculated results with experimental data to give a physical picture of the transition of a metallic contact to an arcing contact. This report discusses a new method of increasing the transition velocity with the use of the sectioned rails and presents results of the new experiments.