A description of the wire explosion process for ETC plasma generators

In an electrothermal-chemical (ETC) gun, electrical energy from a storage device is used to influence the combustion processes that occur within a conventional gun chamber. This typically occurs via a dense, highly nonideal plasma. The ability to simulate an ETC gun system is dependent upon a prediction of the output from the plasma generator. Improvements to a plasma generator computer model have been made as a result of understanding their operation, which has led to significant improvements in the ability to simulate plasma generator operation. However, there is still some way to go before a truly predictive capability can be achieved. This paper is concerned with some improvements to the computer simulation codes and the experimental work that lies behind these improvements. Of particular interest is the mode of the wire explosion process, where the experimental wire ablation rate is far lower than expected from simulations due to anomalous current transfer around the condensed portions of the wire. A new hypothesis is explored that attempts to explain this anomaly. This hypothesis relies upon an electrically insulating metallic vapor transition zone resulting from thermal gradients at the interface between the condensed and plasma phases of the exploding wire. Application of these ideas explains the wire fragmentation process and has also been applied to other areas of capillary plasma generator operation. Further, this hypothesis, if borne out, may have implications for other fields of research such as lightning strikes, electromagnetic gun plasma armatures, and electric armor disruption of shaped charge jets.