Plasma Sheath Dynamics on the Axial Phase of a Plasma Focus Device

Summary form only given. Results on coordinated experiments and MHD simulations on the axial phase sheath dynamics of dense plasma focus are presented. The aim of this effort is to use a repetitively fired dense plasma focus (DPF) to gather data from 100's to 1000's of shots per gas load, so as to better refine numerical codes. The experimental results will feed fully 3D simulations of DPF devices, adding new capabilities to the GORGON code. Experiments are run at DPF-3, a Mather-type PF based at Alameda Applied Sciences Corporation (AASC). This DPF consist of a four-capacitor bank arrangement switched with a rail gap system. Its peak operational current is 480 kA with a maximum stored energy of 5.8 kJ when charged to 20kV, with typical experiments run at 300 kA. The capability of running experiments at 0.33 Hz is key in this project. A typical day's run might gather data from 1000 shots. The relatively large data sets in turn enable a significant statistically analysis, hence a refinement of the GORGON code. The experiments are carried out with Ne at pressures of ~1-4 Torr. This allows control over mass sheath and pinch time, amongst other properties. A non-invasive diagnostic consisting on collimated light emission collected by fiberoptic-photodiode arrays is used to characterize the sheath dynamics on its axial phase at the edge of the anode and cathode. Simulations are run at the Pulsed Power Plasmas Group Cluster, a 96-core HP blade server cluster using 3Ghz processors with 4GB RAM per node, based at UC San Diego. Preliminary results show an average plasma sheath velocity of ~1x105 m/s, where the sheath moves 10% faster closer to the anode. The sheath widths increases by ~20% in the anode-cathode volume, from 1.2mm to 1.5mm. And the moving sheath forms an angle of ~20° between the electrodes. These results are in agreement with the snow-plough model of PFs.