Transition in brush armatures

The use of metal fiber brush armatures incorporated in sabots made of insulating low-density materials in distributed energy storage (DES) railguns requires the avoidance of permanent high-current plasma arcs (contact transition). The resulting plasma might damage the sabot and may also lead to the malfunction of the DES system. In order to determine critical parameters concerning the transition of brush armatures, a series of experiments was performed using the ISL-EMA3 railgun (DES, 3 m, 15/spl times/30 mm/sup 2/, 620 kJ). The maximum muzzle velocity obtained during these experiments was about 1200 m/s. A qualitative model of brush-rail contact, assuming that contact transition is mainly due to mass loss of brushes, is presented. The mechanisms causing mass loss were investigated. It could be shown that joule heating is primarily limiting brush armature performance, while friction is not negligible.