Experiments and Analysis of Downslope Low-Voltage Transition in C-Type Solid Armature Rail Gun

Transition in a rail gun system, namely, the phenomenon of solid contact turns into arcing contact, is undesirable because it is associated with severe damage to both armature and rail. The current downslope (-di/dt) transition is one of the most significant transition mechanisms for C-type solid armatures. In this article, considering velocity skin effect (VSE) and magnetic diffusion processes in armature and rail, a simplified 1-D electromagnetic model is used to illustrate -di/dt effect and verify the occurrence of eddy current. However, further simulation with a 3-D model shows that the electromagnetic force caused by the negative net current in the armature's tail is not the main cause of transition. In addition, a noncontact area between armature and rail is set up to enhance the eddy current, but the resulting reversal Lorentz force is not strong enough to lift off the armature tail from the rail. A set of launching experiments was also carried out using three types of armatures with different tail structures in a 20 mm $\times30$ mm rectangular caliber rail gun. The results show that low-voltage transitions occur when the driving current drops to approximately 90% of its peak value during the downslope.