Measuring Characteristic Differences between High- and Low-Performing Discharges on the MegaJoule Neutron Imaging Radiography (MJOLNIR) DPF

A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a Z-pinch, producing short (<100 ns) pulses of ions, X-rays, and/or neutrons. LLNL recently constructed and brought into operation a new device, the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF, which is designed for flash neutron radiography. This device has achieved neutron yields of up to 4.1e11 neutrons/pulse at 3.3 MA peak current and 1 MJ stored energy. Higher stored energy (up to 2 MJ) commissioning is underway. LLNL runs particle-in-cell (PIC) simulations of DPF discharges in the Chicago code, and has gained significant insight into the various physical factors that influence neutron yield. Optical diodes and the framing camera have enabled run-down and run-in velocity measurements of the plasma sheath. We present measurements from the optical diodes, framing camera, current traces, and voltage probe that are consistent with low-performance shots being plagued by early-in-time current restrikes.