A pulse forming unit for railguns, switched by newly developed high voltage semiconducting devices

The presented pulse forming units (PFU) have an energy of 50 kJ and are driven by capacitors at a voltage of 10 kV. Both as main switch and as crowbar switch newly developed high voltage (U=12 kV) and high power (P>1 GW) semiconducting devices are applied. In order to realize the high blocking voltage the devices (thyristors and diodes) consist of serially stacked semiconducting chips, which are arranged in one common housing. So the size, the inductance and also the resistance of the devices could by reduced by 70 % in comparison to a serial configuration of conventional devices. A special inductor with an inductance of 30 /spl mu/H and a very low resistance of only 2 m/spl Omega/ is used for pulse shaping. So the current yielded from the PFU is limited to 50 kA and the current rise time amounts to about 250 /spl mu/s. To connect the PFU to the railgun highly flexible and low resistive coaxial cables are used. In order to minimize the parasitic inductance the PFU is built up very compactly and coaxially. Thus the losses in the PFU could be reduced and the efficiency of the railgun will be enhanced. As power supply for a railgun a number of 200 PFU will be operated in parallel. Since the PFU are completely decoupled by their inductances, they can be triggered independently from each other. So almost arbitrary current pulses can be shaped by switching on the PFU with different temporal delays.