Development of railgun accelerator at ISAS

A square-bore railgun accelerator system is described in which energy stored in capacitor banks (300 kJ maximum) is supplied to a railgun through a pulse transformer. The use of the transformer reduces the electric current and joule dissipation in the primary circuit while keeping the magnitude of the current in the secondary circuit high. It also makes it possible to use electric components having a low maximum current rating and keeps the current waveform from oscillating without a crowbar. However, if the electric contact between the armature and rail is not complete at ignition the core of the transformer saturates magnetically. This causes very low transformer impedance and anomalously large current in the primary circuit. The performance of the square-bore gun is poor, probably due to the leakage of plasma armature in front of the projectile. The projectile velocity with a hybrid armature is higher than with a plasma armature. The performance is greatly improved by changing to a round bore cross and refining the bore wall precisely with a reamer machine