Insights gained from tests of solid armatures with and without payload in a 15 mm EML

Ten roughly cubical armatures made of three different alloys in two different, albeit similar, designs were tested in an 1.5-cm-bore, 1-m-long EML (electromagnetic launcher), partly with lexan payloads. In payload tests, an arc penetrated between armature and payload sometime during launch. In two cases without payload the armatures broke up early in flight and were overtaken by a runaway arc; the remaining three performed as hybrid armatures, even in a design leaving sizeable gaps between armature and rail surfaces. Speeds up to 2.6 km/s were obtained. Remnants of the armatures and payloads were recovered by soft-catch. Whereas in all cases with payload and with runaway arcs the armatures had broken into pieces, all three armatures without payload and no runaway arc were recovered intact. On the rail sides of these, uniform erosion had removed about 2.5 mm of material. Microscopic study showed that this occurred through superficial melting and spraying off of droplets. Part of the resulting metal aerosol redeposited on the rails, protecting them from significant damage