PERFORMANCE CRITERIA FOR EM RAIL LAUNCHERS WITH SOLID OR TRANSITION ARMATURES AND LAMINATED RAILS

Velocity limitations of EM Rail Launchers with solid armatures due to the velocity skin-effect are assessed for a range of homogeneous materials (copper, aluminium, molydenum and tungsten). Performance criteria as limited by armature melting in the region adjacent to the rail/armature contact surface and by rail surface melting are deduced analytically based on defined electro-thermal reference conditions. The performance criteria predict the reference transition velocity at which the solid contact surface changes to mainly a melted contact surface which is shown to be a fundamental property of the materials. The analysis shows that the critical factors in obtaining a high transition velocity are a relatively high resistivity armature material combined with high temperature rail surface coatings. For example a transition velocity of > 2.0 km/s for a molydenum armature and a tungsten rail surface coating on a copper rail are predicted compared with < 0.5 km/s for the aluminium/copper combination frequently used. Such increase in transition velocity could be important in the development of a solid armature as the first stage of a multi-stage launcher with transition, hybrid and possibly plasma armatures as the later stages.