Discrete pulse forming lines for a compact z-pinch pulsed power generator

A new design for a 1 MA pulsed power supply to drive a z-pinch is being developed in Oxford. The new design avoids the use of very high voltage Marx generators and water pulse forming lines that are usually used in such designs. It should also be far more reliable and capable of a much higher repetition rate, provided the z-pinch channel is preionised using a laser instead of using wires. Thus such a generator would be ideal as a driver for relatively small z-pinches that could act as, for example, a high intensity soft X-ray source. The basic idea is to use many very low impedance pulse forming lines or networks, connected in parallel/series combinations that are DC charged and switched simultaneously on to the z-pinch load. The lines/networks are constructed using either specially shaped tiles of barium titanate ceramics or by using conventional HV ceramic capacitors mounted in such a way as to generate quite square pulses at impedances down to 1 Ω or below. This paper will describe the preliminary tests on a PFN built using thirteen, 60 kV ceramic capacitors (C = 4nF). The line impedance is just 0.8 Ω. It has been found that, provided there is sufficient difference in the inductance on either side of the network connections, it will behave as a pulse forming network and produce pulse rise-times of around 30 ns with a pulse width of 200ns or more. At a 50 kV charge such lines will deliver 50 kA into a short circuit so that 20 such lines operating in parallel can deliver the 1 MA required. It is, of course, very important that each line is switched virtually simultaneously and the results of work exploring this issue will be included. So far it has been possible to synchronise the switch firing jitter between lines to less than 20 ns without the need to use optical coupling or other techniques to aid the synchronization. Finally the design of a 4 line cross device will be discussed which is a preliminary test generator that is being built prior to construction of a 20 line, 1 MA generator.