Experimental Studies of Multi-Wire Arrays on the Cobra Generator

Summary form only given. The rebuilt pulsed power generator, COBRA, capable of providing variable current pulses (e.g., 0.6-1 MA peak current; 100-150 ns rise times), is currently being used to study wire array Z-pinch implosions at Cornell University. Wire arrays constructed from four, eight, and twelve wires of aluminum, nickel, tungsten, Invar (Fe, Ni alloy), as well as other materials, have been tested. Various array diameters have also been tested, although typically 1.6 cm has been used, and the standard array height is 20 mm. The influence of the current waveform on the array implosion has been studied using X-ray imaging diagnostics with spatial and/or temporal resolution. Photodiodes such as XRD, PCD, and AXUV-HS were used with various filters to investigate a wide energy range that spanned from EUV up to 10-keV X-rays during various stages of the array implosion process. Characteristic to this research was the use of X-ray backlighting, which was employed to focus in on the explosion processes of the individual wires during an array implosion. The source of the X-ray backlighting was two, four-wire X pinches made from either aluminum or molybdenum wires. These X pinches replaced two of the four standard electron return current posts in the anode hardware setup, and were capable of providing the desired point-projection backlighting. This imaging technique made it possible to determine the expansion rates and inner structure of the various wire cores, as well as to observe the development of sausage instabilities. Additionally, a spherically bent mica crystal spectrograph and a flat KAP crystal spectrograph were used to determine plasma parameters for both the X pinches and the main wire array. Pinhole cameras were also used, and provided wide view images of the entire configuration. The images consist of a full view of the main array, with an X pinch off to either side. By using various filters with these pinhole cameras, potential problems associated wit- the wire contacts at the electrodes were observed. These observations have been examined to understand the influence of contact points on precursor plasma formation