Medium-Bore Helical-Coil Electromagnetic Launcher with A Liquid Nitrogen Cooled Armature

Continued investigations of medium-bore helical coil electric launchers (HCEL) at the University of Missouri-Columbia are presented and discussed. The HCEL under investigation has an armature diameter of 40 mm and a stator length of 750 mm. The HCEL inductance gradient is 150 muH per meter and is a factor of 300 times greater than the inductance gradient of a conventional railgun. The HCEL armature forms the projectile and is typically on the order of 500 grams. The HCEL is powered by an eight module, 125 kJ sequentially fired pulse forming network that can deliver 10 to 15 kA peak current pulses over an 8 ms period. In this investigation, HCEL performance enhancements accomplished with a liquid nitrogen cooled armature are quantified and compared to theoretical predictions. The liquid nitrogen cooled armature winding is constructed with commercial grade aluminum wire. Measurements have shown that liquid nitrogen cooling produces a factor of 8 decrease in armature resistive losses. Theoretical predictions show that with a factor of 2 decrease in total resistive loss (i.e., armature plus stator resistance), an LNCA operating at a velocity of 150 m/s should produce an overall electrical to kinetic energy conversion efficiency of 30%. The experimental results confirm these theoretical predictions.