Experimental investigation of the ablation of wire arrays

Summary form only given. The ablation phase of wire arrays drives streams of material to the common axis for long periods of time prior to implosion. Flow conditions determine the density profile encountered by the imploding array, influencing trajectory and kinetic energy at stagnation. Understanding the ablation process is key to the continued development of wire arrays as a candidate for fusion. The phenomena observed during the evolution of the array can be used to analyze the underlying ablation processes. The electrical breakdown of a metal wire, and formation of the core-corona structure, is often characterized by a collapse of the voltage across a wire load. If wires are initially insulating, (e.g. plastic coated) the initial condition for breakdown are substantially different, and the injection of mass into the array and subsequent implosion may proceed differently. Following initiation, ablated plasma streams show an axial modulation, the origin of which is currently unknown. This is often attributed to M=0 MHD instabilities local to each wire. Arrays which endeavor to alter the local magnetic field configuration at the wire may provide information on the dominant processes during this complex ablation behavior. The appearance of the precursor column is evidence of mass distribution during an experiment. Once formed, the variation of column density with time provides a time history of material ablated from the wires. Quantitative measurements can be compared to modeling to directly estimate mass ablation rates. An experimental investigation of the situations described above will be presented, with a view to providing further evidence as to the dominant processes during the ablation phase of wire array Z-pinches. Time resolved, quantitative diagnostics provide a time history of the density profile during the current drive, and this data may give a clearer indication of the ablation processes at work. Comparisons to current ablation modeling will also be discussed