STUDIES OF INDUCTIVE PLASMAS AND THEIR APPLICATION TO THETA- PINCH DEVICES VIA NUMERICAL MODELING by WARNER

First, a globally-averaged RF plasma model is used to investigate exit conditions immediately following a RF pre-ionization stage. Analysis shows that reducing pulse duration from 10 to 10 seconds increases peak ion energy fraction by 17% (from 16 to 33%) and doubles final conductivity. Pulse waveforms are square in nature, and ion energy fraction is defined in this work as the percentage of total input energy entrained in ions. Increasing total energy deposition from 5 to 160 mJ increases ion energy fraction from 33% to 58% at a 200 ns pulse duration. This increase is not linear however, showing instead a diminishing return with a peak fraction plateau estimated at 65% to 70%. A constant (time-average) power analysis reveals that, across all power levels (10 to 100 kW), energies (5 mJ to 1 joule), and durations (0.05 to 10 μs), peak ion energy fraction consistently occurs approximately 1 to 2 μs before peak conductivity. Second, single particle and particle-in-cell simulations are used to elucidate breakdown physics in a ringing theta-pinch with bias magnetic field. The analyses presented here agree with previously conducted experimental results showing that gas breakdown occurs only upon approximate nullification of the bias magnetic field by the pulsed theta-pinch magnetic field. Parametric analysis of the peak electron energy as a function of the bias and pre-ionization magnetic fields reveals that; 1.) when bias magnetic field is ≈ 97% of the pre-ionization magnetic field the peak electron energy is highly erratic, and 2.) high electron energy levels require a pre-ionization to bias magnetic field ratio of 2 to 1 or higher. This second work went on to be published in the Phys. of Plasmas Journal, Vol. 19 (2012, http://link.aip.org/link/doi/10.1063/1.4717731).