Electrical and thermal effects of rail cladding

Achieving long rail life may require the use of a thin surface cladding of hard, refractory material. This paper reports numerical simulations of the effect of a resistive cladding on railgun efficiency. Simulations are perfo rmed using a three-dimensional (3-D) finite element code, Electro-Mechanica l Analyses Program in 3 Dimensions (EMAP3D), that is capable of tracking mo ving conductors. Current and temperature distributions are calculated in to w regions of interest: i) behind the armature-where current diffuses into t he rail in a two-dimensional manner, and ii) in the portion of the rail adj acent to and under the armature-where current flow is fully three dimension al. The railgun model used for these simulations has a 40-mm square bore wi th a 1-mm thick cladding on the rail surface. The increase in electrical lo ss due to the cladding is a function of axial location and is largest where the armature velocity is low. We find that combined 2-D and 3-D effects ca use a total additional thermal loss equal to about 5% of the muzzle energy when the cladding resistivity is 10 or 50 mu Omega.cm. The decrease in tota l launcher efficiency is less than 1%.