Railgun simulations: Foil breakdown and plasma armature growth

Summary form only given. As part of a railgun research program at the Naval Research Laboratory, a numerical simulation capability has been developed for a full bore model of a railgun from the driver circuit and injector gas, through the foil breakdown, to plasma armature formation and projectile acceleration. The 1-D Lagrangian code solves the resistive magnetohydrodynamic single-fluid equations along the axial direction with an assumed temperature profile in the lateral direction. Thermal conduction along the axis and to the walls is accounted for. A study of collisional-radiative equilibrium for a boron plasma under typical railgun armature conditions verifies that the stricter assumption of local thermodynamic equilibrium is sufficiently accurate. The present initial results emphasize the electrothermal forces imparted to the projectile by the Al foil breakdown with a proper equation-of-state and electrical conductivity model. Phenomenological models for the insulator ablation and erosion of the rails are included and lead to the enhancement of the armature mass.