Improvements in Pinch Formation Using Tapered, Hollowed Anodes in a MJ-Class Dense Plasma Focus

A dense plasma focus (DPF) device drives current through a set of coaxial electrodes to assemble plasma inside the device and implode the plasma on axis to form a Z-pinch. The implosion drives instabilities to generate strong electric fields, which produce short intense pulses of x-rays, high-energy (>100 keV) electrons and ions, and if using fusion-reactant ions (e.g. D, T), will generate neutrons. As well as being dependent on the high-energy ion “beam”, neutron production relies on the formation of a long, high-density, “plasma target” that the ions will pass through. Using the particle-in-cell code Chicago in 2D-3V, we simulate the plasma target formation in a multi-mega-amp DPF device. We find that adding a taper and a hollow to the inner electrode (anode) improves the formation of the plasma target on axis by creating a more uniform implosion. The taper is most helpful for large radius anodes and is a potential method for mitigating yield roll-off at high currents (3+ MA). We investigate the importance of the electron temperature of the plasma target on the ion stopping power to understand the optimization of the anode shape. We also describe how to achieve a given neutron yield based on estimates of the ion beam & plasma target.