Inductive energy storage and homopolar generators

The pulse power requirements for an electromagnetic railgun depend primarily on the energy required for the projectile, the time of flight in the railgun barrel, and the barrel efficiency. One of the most usual railgun power sources is the DC homopolar generator (HPG). A major shortcoming of the HPG is that it produces a low EMF (usually little more than 100 V) and it cannot therefore deliver the required power directly to the rails. Instead the HPG is used with a suitable inductor which acts as an intermediate energy store (IES). The inductor will usually be charged over a period of 100-200 milliseconds (the rise time) and then rapidly discharged into the rails (barrel time) so as to produce the required voltage for projectile acceleration. There are two types of inductor, solenoidal and toroidal. The author describes toroidal inductors, which are air-cored, for use with HPG. The key parameters of the inductors are discussed. These are: resistance, stray field impacts, EM stresses in the coil, and the skin effect