Low Impedance Z-pinch Drivers Without Post-Hole Convolute Current Adders

Abstract

Summary form given only. Z-pinch radiation source drivers such as Z and ZR must supply very high currents at moderate (by pulsed power standards) voltage. This in turn requires very low inductance feeds. Presently this is accomplished by adding several higher impedance drivers in parallel using a post-hole convolute current adder. Unfortunately, current addition results in localized magnetic nulls that extend from the cathode to the anode. Since the cathode surfaces emit electrons at the space-charge limit, the nulls result in electron losses. These losses are in addition to those due to magnetically insulated flow over most of the transmission lines, and, more importantly, these losses at magnetic nulls are lost over small areas of the anode resulting in electrode damage and conducting gases that cause major current losses and further damage. It is possible to replace the current adder (convolute) with an auto-transformer that will allow driver power to be combined in series with voltage adders, and then to be converted to lower voltage and higher current in the auto-transformer. In contrast to common transformers, this transformer consists of coils whose windings are in parallel rather than series. These coils would be similar to the coils found in a number of other pulsed power devices such as some ion diodes and triggered plasma opening switches. There are several potential benefits to using an auto- transformer approach. Such a system would have no magnetic nulls to cause localized current losses. Moreover, the current multiplication ratio can easily be varied, resulting in a more versatile driver. There are also potential benefits in the way the wire loads would be installed that should increase the shot rate. The critical issues that must be addressed are achieving sufficient coupling between the primary and secondary circuits, and building a primary coil with adequate mechanical strength. This paper will describe the design of such a system, and will present results analyzing the performance of such a system in comparison to the standard post-hole convolute approach.