Locating restrikes in the MJOLNIR Dense Plasma Focus

A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a z-pinch. The MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF at LLNL is designed for flash neutron radiography and has achieved neutron yields up to 3.8E11 neutrons/pulse at 2.5 MA peak current with 1 MJ of stored energy. We hypothesize that current is being diverted from the pinch (also referred to as restrikes) and lowering the neutron yield based on the correlation between current traces and yield. For shots with smaller inductive current dips (and smaller yields) restrikes need to be added in simulation to attain the best match to the experimental data. This suggests that restrikes are occurring somewhere in the DPF head and are causing lower neutron yields. In order to determine if, and where, current is being lost a set of B-dot probes and Rogowski coils have been developed. Both the probe designs and preliminary results from this set of new diagnostics will be presented.*