Optimization of Electrodynamic Energy Transfer in Coilguns With Multiple, Uncoupled Stages

A 1-D model for inductive electromagnetic acceleration of projectiles using a coilgun has been nondimensionalized to find relevant scaling parameters. The dynamic impedance parameter, representing the ratio of the resonant period of the unloaded electrical circuit to the time the projectile is electromagnetically coupled to the coil, is the scaling term that can be adjusted to optimize the electromagnetic energy transfer process. The mutual inductance profile, which represents the ability to convert potential electromagnetic energy into projectile kinetic energy, was modeled for a specific geometry using a semi-empirical function previously found suitable for cylindrical pulsed inductive plasma accelerators. Contour plots representing coilgun efficiency were generated for varying initial projectile velocity across a range of dynamic impedances. The contour plots show that below a given initial velocity a dynamic impedance parameter can be selected to maximize energy transfer to the projectile. This optimum varies as a function of the initial velocity a projectile possessed when it enters the coilgun stage. Once the contour plot is generated for a geometry it can be used to optimize the acceleration process for any stage in a coilgun if the individual coils comprising the stages are electromagnetically uncoupled from each other and the velocity of the projectile as it exits the previous stage is known.