Multi-radiation yields simulation and optimization of plasma focus devices

Abstract

The plasma focus device is a potential source of multi-radiation emission. Numerical experiments were performed to study the multi-radiation emission of soft X-ray and neutrons from Mather type plasma focus devices with energies ranging from 1.4 kJ to 480 kJ operated in deuterium and argon gases. This device was chosen since it provides an open geometry with large possible collection angles operated over wide parameter ranges. However, the study of optimum gas pressure, current sheath speed, and pinch current is still required for a better understanding of the device. In this study, the Lee’s Code version RADPF6.1b was used to perform the current profiles fitting process. The mass sweeping and current factors for axial and radial phase were used to accommodate the conditions encountered in the experiments. All gross properties including the radiations were realistically modelled once the computed and measured current profiles are well fitted. In the case of 1.4 kJ plasma focus device, the optimum computed neutron yield, Yn was 2.9 × 107 neutrons/shot at 5.5 Torr deuterium pressure. The optimum computed Yn of 1.447 × 108 neutrons/shot for 11.2 kJ plasma focus device was achieved at 4.1 Torr. For 28.8 kJ device, the optimum computed Yn of 1.24 × 109 neutrons/shot was obtained at 2.2 Torr deuterium pressure at 20 kV. For the 480 kJ device, the optimum yield of 1.8 × 1011 neutrons/shot was obtained at pressure and charging voltage of 7.6 Torr and 27 kV respectively. Analysis of the results showed that the optimum neutron yields were achieved only at optimum operating conditions. It was also found that no soft X-rays were emitted from the 28.8 kJ plasma focus operated in argon gas due to the absence of Helium-like and Hydrogen-like ions at the recorded low plasma temperature of 0.094 keV and axial speed of 8.12 cm μs-1. In conclusion, the current sheath speed is not a dominant factor for optimizing neutron yield in plasma focus devices.