Simulation-Guided Experiments on the Megajoule Neutron Imaging Radiography (Mjolnir) DPF

A dense plasma focus (DPF) is a relatively compact coaxial plasma gun which completes its discharge as a Z-pinch. These devices have been designed to operate at a variety of scales in order to produce short (<100 ns) pulses of ions, X-rays, or neutrons. LLNL has recently constructed and brought into operation a new device, the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF, which is designed for radiography and high yield operations. This device has been commissioned and has achieved neutron yields up to 4E11 neutrons/pulse at 2.2 MA pinch current while operating at up to 1 MJ of stored energy in 2019. The MJOLNIR driver has been upgraded from 1 MJ to 2 MJ stored energy and is expected to achieve 4 MA peak current with this upgrade. First results from shots taken with the upgraded driver will be presented. MJOLNIR is equipped with a wide range of diagnostics, including activation foils, neutron time of flight detectors, a fast framing camera, optical light gates, and a time-gated neutron and x-ray imager. LLNL also runs unique particle-in-cell (PIC) simulations
^1–3
of DPF discharges in the Chicago code, and has been able to gain significant insight into the various physical factors that influence neutron yield. To that end, MJOLNIR is one of the first DPFs whose design and continual upgrades are heavily influenced by model predictions. In this presentation, we will describe insights from modeling, device operation, and recent results. Comparisons between the modeling predictions and measurements, as well as x-ray and neutron images will be presented.