In Situ Electromagnetic Probes to Track Current and Diagnose Restrikes in the MJ Class 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. Experimental and simulation efforts are currently underway to improve our understanding of current flow in MJOLNIR and the role of restrikes in limiting the DPF yield. This presentation will discuss a set of B-dot probes and Rogowski coils placed in several locations along the power flow region to measure current delivery to the pinch region at pinch time. By placing these probes at the base of the DPF head, along the DPF head, and on the return current resistors, we will be able to quantify how much current is being lost before the pinch. Design work on these probes center on lowering probe inductance and improving electrostatic shielding to produce cleaner signals with a larger frequency response range. Probe designs, calibration routines, and preliminary results will be presented.