Investigation of the Plasma Current Sheath Dynamics in the Run Down Phase of the Hemispherical Plasma Focus Devices Using Two-Dimensional Time Dependent Modeling

The Hemisphere Plasma Focus (HSPF) device is a new construction in which the discharge takes place between two concentric hemispherical electrodes. A 2D snow plow model is designed in order to simulate the distributions of the HSPF characteristics between the two electrodes. The model used the momentum and circuit equations to describe the different characteristics in the rundown phase such as; the distributions of the magnetic field, the sheath velocity, the sheath displacement, and the plasma temperature. The results show that the simulated discharge current is in a good agreement with the experimental signal for input charging voltage of 3 kV and helium gas pressure of 0.6 Torr. The peak discharge current is about 42 kA with rise time of about 8.5 μs and the rundown phase is completed at time of about 6.5 μs. The timelines of the current sheath displacement show that the sheath has almost an umbrella shape. As the current sheath is accelerated in θ-direction towards antipodal point, the magnetic field and the plasma temperature are increased and their values are higher as one goes closer to the inner electrode.