Why solid armatures fail and how they can be improved

Abstract

Failure of electromagnetic launch (EML) solid armatures can be caused by various mechanisms, but a critical performance limit is due to arcing at the rail/armature contact surface above the transition velocity. A previous theoretical transition model based on velocity skin effect and current wave (VSE/CW) phenomena is reviewed and further data of the changing current distribution at the contact surface is derived as the vaporization current wave moves forward until the arcing transition occurs. This VSE/CW model predicts experimental transition velocities with reasonable accuracy over a wide range of parameters (bore size from 15 to 90 mm). To achieve the required contact pressure distribution with the optimum contact region geometry, monolithic armatures are considered to be necessary, which is consistent with the highest transition velocities being achieved with such aluminum alloy armatures. Possible improvements in the performance of solid armatures are evaluated for monolithic armatures with copper rails by optimizing armature geometry, dimensions, contact pressure distribution, and the use of resistive contact region materials. An increase of >40% in transition velocity to >2.5 km/s is predicted above reported experimental results.