Prediction and verification of electromagnetic forces in helical coil launchers

Calculating the circuital parameters and electromagnetic force production between two coupled coils is critical when modeling helical coil launchers (HCLs). Computer tools that calculate the self inductance, mutual inductance, and inductance gradient of a coupled-coil pair are developed for the PSpice circuit simulator. The inductance values and gradient are used to model a short (16.3-mm length), small-bore (19.4-mm diameter) HCL. The HCL is constructed in the laboratory and its performance is measured. The HCL accelerated nominal 16-g projectiles up to 170 m/s using a 6-kJ capacitive energy store. The highest overall electric-to-kinetic conversion efficiency was 5.4%. Comparisons are made between the theoretical and experimentally measured launcher parameters. In general, there is good agreement between the predicted and measured HCL parameters.