Optimizing Dense Plasma Focus Neutron Yields with Fast Gas Jets*

We report on a study using the particle-in-cell code Chicago to perform fully kinetic simulations of dense plasma focus (DPF) devices with patterned gas loads created via supersonic gas jets on axis. The supersonic jets are modeled in the large-eddy Navier-Stokes code CharlesX, which is suitable for modeling both sub-sonic and supersonic gas flow. The gas pattern, which is essentially static on z-pinch time scales, is imported from CharlesX to Chicago for neutron yield predictions. Fast gas jets allow for manipulating the mass on axis while maintaining the optimal background pressure for the DPF. The conditions favorable for producing neutrons are found to be more consistently met when a jet is present on axis. Perturbations in the jet density introduced via super-sonic flow (known as Mach diamonds) allow for consistent seeding of the m=0 instability, producing a better ion beam, and consistent target formation leading to more consistent ion acceleration and higher neutron yields with less variability. The optimal jet configuration for increasing neutron yield and reducing shot-to-shot yield variability is explored.