Design Considerations of an Air-Core Pulsed Alternator in an Electromagnetic Railgun System

An air-core pulsed alternator is extremely attractive for driving the electromagnetic launchers. The reason is that the machine can offer high voltage and current performance in a single-element energy storage device, a smooth pulse profile, and naturally cycled current zeros, which can allow for extremely low muzzle currents and simplifies switching requirements. But because of the short history of the air-core pulsed alternator in China, the relevant theoretical research is not enough and the experience in fabrication is absent. It is really necessary to summarize a preliminary design method in order to rapidly determine the size and approximately evaluate the electrical performance of the machine. The optimization will be based on this first-stage design scheme. In this paper, based on the requirements of the railgun, some important design considerations of a seven-phase and six-pole air-core pulsed alternator are presented in detail. In addition, it is significant to obtain the analytical formulas for the first-stage design requiring less costs; these formulas intuitively allow us to expedite the design process and optimize the design scheme. Finally, some basic output parameters of the machine are given for the preliminary design; the designed pulsed alternator will generate 1.4 kV and drive a train of 1-MA pulses into a 5-m railgun, accelerating 200-g masses at 2 km/s.