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 performed using a three-dimensional (3-D) finite element code, Electro-Mechanical Analyses Program in 3 Dimensions (EMAP3D), that is capable of tracking moving conductors. Current and temperature distributions are calculated in two regions of interest: (i) behind the armature-where current diffuses into the rail in a two-dimensional manner, and (ii) in the portion of the rail adjacent to and under the armature-where current flow is fully three dimensional. The railgun model used for these simulations has a 40 mm square bore with a 1 mm thick cladding on the rail surface. The increase in electrical loss 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 cause a total additional thermal loss equal to about 5% of the muzzle energy when the cladding resistivity is 10 or 50 /spl mu//spl Omega/.cm. The decrease in total launcher efficiency is less than 1%.