Arc motion in railgun plasma armatures

H.H. Maecker´s theory (1971) for arc motion and displacement is extended to the pressure-dependent arc conditions found in railgun armatures. It is shown that for the railgun plasma armature there are thermal mechanisms, which do not exist for solid armatures, that tend to move the peak of the current density forward toward the base of the projectile, thereby mitigating the tendency of the velocity skin effect to concentrate the current density toward the rear. This effect may explain the variance between some theoretically predicted current density profiles in plasma armatures and those measured by B-dot probes