COMPACT 50-KJ PULSE FORMING UNIT, SWITCHED BY SEMICONDUCTORS

Compact pulse forming units for the 10 MJ-facility PEGASUS have been designed and constructed. Each unit consists of a 50 kJ-capacitor, a thyristor stack as main switch, a semiconducting diode stack as crowbar switch and a compact pulse forming inductance. For the PEGASUS facility a pulse forming network of 200 basic units is required. The maximal operating voltage of each unit is 10 kV and the current pulse yielded has an amplitude of up to 52 kA with an increasing time of 230 mu s. To minimize the electrical power dissipation in the primary circuit the pulse forming unit was built up very compactly and coaxially. The inductance in the primary circuit consisting of the capacitor, the main switch and the crowbar switch is less than 120 nH. Thus the reverse voltage measured at the capacitor is reduced to only 4 % of the original voltage and the electrical power dissipation is negligible. The pulse forming units are connected to the railgun by flexible coaxial cables. Since the main switch consists of a high voltage thyristor, the operating voltage can be varied continously between 0 kV and 10 kV. The parallel operation of several pulse forming units is feasible and the standard of security is very high, because the units are decoupled completely by a pulse forming inductance of 30 mu H. With a special trigger unit each 50 W-capacitor can be switched independently. So an almost arbitrary current pulse can be formed by switching several units with temporal delays. Therefore and due to the negligible electrical power dissipation in the pulse forming unit the overall efficiency of the railgun can be enhanced.