Pre-ionization Studies on the Modular Theta-Pinch Experiment (MTX) for Field-Reversed Configuration (FRC) Formation*

The density, temperature, flux retention, and stability of an equilibrium Field-Reversed Configuration (FRC) strongly depend on the parameters of the pre-ionized plasma prior to field-reversal. Studies have been conducted on the Modular Theta-Pinch Experiment (MTX) at Los Alamos National Laboratory investigating the plasma density, uniformity, and magnetic field diffusion using the ringing-theta and ringing-multipole pre-ionization methods. Semi-empirical models predicting electron source rates at early time for these methods have been developed in order to better predict the conditions necessary for breakdown and are compared to experimental results. The effects of seed ionization provided by fast-rising bias fields and an annular array of coaxial plasma rail guns have also been investigated. The resulting plasma conditions from various combinations of seed and pre-ionization methods are discussed within the context of FRC formation.