MHD Simulation of Hemisphere Plasma Focus Using Snowplow Model

The Hemisphere Plasma Focus (HSPF) device is a new construction of plasma focus (PF) devices wherein the discharge takes place between the inner and outer concentric hemispherical electrodes with total energy up to 3.4 kJ. The pinch effect appears in the shape of a sharp crevice in the discharge current signal. HSPF is simulated by utilizing the Snowplow Model depending on the circuit equation incorporated with the momentum equation. Some modifications were added to the model to improve the theoretical data in order to be consistent with the experimental results. The code includes a rundown phase starting from the equator point toward the antipodal point and the reflected shock phase at the axis. The model results are compared with experimental results, and the effect of discharge parameters such as the discharge voltage and helium gas pressure on the plasma parameters is studied. The total system inductance is about 285 nH with a resistance of about 23 mΩ. Furthermore, the plasma inductance has a maximum value at the pinch time, which is decreased by increasing the charging voltage or decreasing the gas pressure. The mass factor in the HSPF device is found to be relatively low compared to that of the coaxial PF device. The shock front and current sheath velocities are increased by increasing the drive factor while the pinch time is decreased. Also, the minimum pinch radius and the plasma inductance have a reverse trend as a function of the drive factor.