| The longevity of electro-magnetic launchers is affected by the occurrence of arcing transition. Solid-on-solid sliding contact, under the action of Lorentz force, is lost as high levels of current, up to several mega amperes, and high levels of velocity, up to kilometers per second, generate interfacial heat that melts the armature contact surfaces at rates approaching 1 mm of depth lost per meter of sliding. This wear depth is in excess of sacrificial armature material thickness available, producing gaps and loss of solid-on-solid contact between sliding surfaces. Loss of contact causes arcing transition, a damaging occurrence to the launcher rails and potentially dangerous to the launch package.;Modeling and experimental studies address the high wear rate of melting. The rail conduction effectiveness (RCE) quantity is developed as a guiding parameter in choosing armature/rail material combinations. The RCE is successfully evaluated in ring-on-rod, pin-on-rail and actual electro-magnetic launcher contacts. Molybdenum is identified by consideration of the RCE as an armature material that launches on copper rails without occurrence of arcing transition. To keep the parasitic mass of armature low an aluminum armature with molybdenum claddings is designed and also successfully launched with arcing transition not occurring. |
