Influence of lubricant on the motion of a body in an electromagnetic railgun accelerator.: I.: Electric current distribution in the accelerated body and the rails

An investigation is made of the influence of a liquid conducting film inserted in the gap between the accelerated metal projectile and the rails in a railgun accelerator on the distribution of the current density and the magnetic induction in the rails and the projectile. The film is assumed to be fairly thin, so that the variation of the magnetic induction across the film can be neglected. The problem is considered in a plane geometry. Approximate expressions are derived for the thickness of the velocity skin layer as a function of the thickness and conductivity of the film. The equations for diffusion of the magnetic field in the rails and in the projectile are integrated numerically. It is shown that the presence of a liquid conducting film can significantly suppress the velocity skin effect. Nevertheless, even when fairly thick films of fairly high resistivity are used, the nonuniformity of the electric current density distribution in the projectile still remains very high for the magnetic Reynolds numbers of practical interest. (C) 1999 American Institute of Physics. [S1063-7842(99)02207-2].