High-Efficiency Helical Coil Electromagnetic Launcher and High Power Hall-Effect Switch

摘要

Efficiency and scaling relationships for DC (i.e., non-induction) constant inductance gradient electromagnetic launchers are presented and discussed. Expressions for electromagnetic force, efficiency, back-voltage, and kinetic power are derived and given in terms of electrical circuit parameters. Launcher efficiency is shown to be a simple function of armature velocity and the launcher's characteristic velocity. The characteristic velocity characterizes the launcher and is the product of two new parameters; the mode constant and launcher constant. Mathematically, the launcher must operate at its characteristic velocity for 50% maximum efficiency. The mode constant reflects the manner in which the launcher is powered and its maximum efficiency. The launcher constant reflects the geometry of the launcher. The two modes of operation presented in this investigation include constant current and zero exit current operation. The ideal electromagnetic launcher concept is developed and defined by operation at 100% maximum efficiency at all velocities. The concept of same-scale comparisons is developed and states that electromagnetic launcher comparisons should be done with equal bore diameter, launcher length, projectile mass, and velocity. A comparative analysis using experimental data of same-scale constant gradient electromagnetic launchers is performed with conventional railgun, augmented railgun, and helical gun launchers and is presented in terms of the launcher constant, inductance gradient, bore diameter, bore length, system resistance, and armature (i.e., projectile) velocity. A theoretical analysis is also presented to design a helical electromagnetic launcher for a specific volt-amp characteristic. Experimentally measured performance is reported for a 40 millimeter bore helical electromagnetic launcher which is subsequently compared to a one-turn augmented railgun and a conventional railgun operating at comparable scale.