Comparison of implosion characteristics of gases in a 1.5 kJ plasma focus

Summary form only given. The implosion time is an important parameter for the performance of a Z-pinch. Conventional radial Z-pinches tend to implode most, if not all the mass, leading to a simple scaling relation based upon current, linear mass density, implosion time and initial mass radius. The plasma focus snowplows only a small fraction (<;10-20%) of the available mass between the anode and the cathode. The mass fraction is likely to depend on the electrode geometry, gas type and current pulse.In this study, we examined a plasma focus with a fixed electrode geometry and charge voltage on the driver bank. The gas pressure and gas type were varied to examine the changes in implosion time. Tens of shots were used at each operating condition. The standard deviation in the implosion time was found to be less than 5% in most cases. Relationships were derived between the gas mass density and the current for different gases. Using a formulation developed by Lee in his 1D plasma focus model, a normalized mass fraction and normalized current fraction were derived based upon the experimental data. The experimentally derived fractions were compared to Lee´s model and reasonable agreement was achieved in the normalized fractions.