Utilization and Optimization of Superconducting Coil Parameters in Electromagnetic Launcher Systems

The utilization of external field windings in electromagnetic launchers provides an additional electromagnetic field between the rails of an electromagnetic launcher which increases the Lorentz force acting on the armature in the acceleration direction. However, additional magnetic field created by the conventional copper windings are very limited due to their low maximum current carrying capability. Therefore, using high temperature superconductors (HTS) with a current carrying capability up to 100 A/mm2 for the external coils can be used to increase the magnetic field density between rails. This paper presents an optimization study for the design of two external coils with rectangular tape YBCO superconducting wire. The HTS coils are proposed to increase the efficiency of a 3 meter long launcher with 25 mm x 20 mm rectangular bore caliber. The optimization parameters are selected as the magnitude of the DC coil current, the coil position, the number of turns of the coil, and the number of coil layers. Also, the objective function of the optimization is the electromagnetic force acting on the armature, which is dependent of the rail current and B field on the armature. During the operation of the launcher and the external coils, it is critical to prevent quenching of the HTS coils due to the perpendicular and tangential magnetic field on the coils, temperature and current density of the coils. In order to estimate the quench and calculate the objective function, finite element analysis (FEA) is used in 2D. Real coded genetic algorithm (RCGA) is also used as optimization method. The results of the optimization study shows that HTS coil augmentation is feasible for small caliber railguns. The HTS coil position is limited by cryogenic chamber and rail containment dimensions. The maximum coil current is determined by the self field due to cancellation B field generated by the rails and the coils. For 500 kA rail current the force acting on the armature increases from 55 kN to 70 kN with and increase rate of 26%, a muzzle velocity increase from 1650 m/s to 1900 m/s with an increase rate of 12% and a muzzle energy increase from 160 kJ to 210 kJ with and increase rate of 25% when external HTS coil augmentation is used.