The Dynamics Of Multiple Plasma Armatures In Railguns

The predicted performance of plasma armature hypervelocity railguns has rarely been achieved in experiments. These failures are usually accompanied by the formation of multiple arcs which are often described as restrikes or secondary arcs. We have investigated the dynamics of formation and evolution of these multiple arc structures using both dynamic circuit models and two-dimensional MHD computational codes. It appears that multiple arcs in railguns are created by the division of the primary arc into two arcs separated by a region which does not carry current. The subsequent motion of the two arcs is determined by the interaction of electromagnetic and hydrodynamic forces and the dynamics of the changing electrical circuit. A model was developed to simulate this complex behavior which includes the time dependence of the inductance and resistance of the railgun and the ablation of the railgun bore. This model was used to interpret some earlier LLNL experiments reported by Hawke et al., and showed that their observed velocity limit occurred when the primary armature separated from the projectile within the bore.