First measurements of current distribution in moving fiber-armatures in railguns

Using miniaturized Rogowski coils developed at ISL, we are able to measure the currents flowing through moving metallic fiber-armatures in a railgun. The 15 mm square bore railgun is 0.5 m in length and is powered by a 150 kJ capacitor bank. The peak current is about 200 kA and typical launch velocities with this test bed reach 600 m/s. The armature consists of two fiber brushes made of the same metal (e.g. Cu-Cd) or two different metals (e.g. brass and Cu-Cd). The current distribution between the two brushes has been measured during the shot. A special voltage probe placed on one rail provides information about the rail resistance variation during projectile passage. A comparison between the experimental results and the current distribution calculated with a three dimensional finite element code, taking into account thermal effects, is presented.