Ionization dynamics of a single wire z -pinch.

This thesis explored the ionization dynamics of a single wire z-pinch. Experiments were conducted on fine wires of aluminum, copper, silver, and tungsten ranging in diameter from 7.5--50mum with lengths of 2.5cm. These wires were subjected to a pulsed current of ∼2kA, 500ns half-cycle from a spark-gap triggered, negatively-charged capacitor bank discharge. The results of this thesis are divided into three parts which cover the entire dynamic evolution of the wires during the first ∼500ns of the current pulse. The first part examined surface impurity evolution and its contribution to the voltage collapse and initial plasma formation. It was discovered that hydrocarbon impurities contribute significantly to the initial plasma formation, for all wires studied, and that high ionization states of carbon (CIII and CIV) are present at the point of the voltage collapse. The second portion of the thesis dealt with laser imaging and the observation of instability growth at the core/corona boundary of expanding z-pinch wire plasmas. From the increased sensitivity of the resonant XeCl excimer laser diagnostics, it was determined that, for aluminum wires, these instabilities were consistent with a hydrodynamic Rayleigh-Taylor instability of a decelerating plasma plume front. The third portion of the thesis focused on potential seeding mechanisms for instability growth in single wire z-pinches and their relevance to wire array experiments. It was observed in copper wires that do pre-heating of wires caused surface alterations due to recrystallization. It was also discovered, during the course of these studies, that electrical current pulses on the timescale of the experimental pulse (500ns half-cycle) could also alter the surface structure of copper wires and lead to coronal instabilities. Finally, preliminary investigations into the possibility of crystal/grain growth behavior in tungsten wires is given, along with the idea of using potassium doped tungsten wires as a means of compensating for this behavior in pure tungsten. The experiments in this thesis were designed with the intention of aiding in the overall understanding of z-pinch wire physics and in particular the pre-pulse conditions on larger wire array experiments, such as the Z-machine at Sandia National Laboratories. The information in this thesis is directed towards supporting ongoing modeling efforts to help establish the initial conditions for individual wires on wire arrays, with the overall goal of being able to better predict wire array behavior. (Abstract shortened by UMI.)Ph.D.Applied SciencesNuclear engineeringNuclear physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124443/2/3138187.pd