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Authors: McBride, Ryan
Keywords: wire-array z-pinch
plasma physics
x-ray radiation source
high-energy-density physics
Cornell COBRA accelerator
pulsed power
Issue Date: 30-Oct-2008
Abstract: This dissertation presents the results of two experimental studies of wire-array z-pinches on the 1-MA, 100-ns rise-time Cornell Beam Research Accelerator (COBRA). In the first study, results are presented which characterize the implosion dynamics and radiation output of wire array z-pinches on COBRA. Here the load geometries investigated include 10- and 20-mm tall cylindrical arrays ranging from 4 to 16 mm in diameter, and consisting of 8, 16, or 32 wires of either tungsten, aluminum, or Invar (64\% iron, 36\% nickel). Diagnostics fielded include an optical streak camera, a time-gated extreme-ultraviolet framing camera, a laser shadowgraph system, time-integrated pinhole cameras, an x-ray wide-band focusing spectrograph with spatial resolution, an x-ray streak camera, a load voltage monitor, a Faraday cup, a bolometer, silicon diodes, and diamond photoconducting detectors. The data produced by the entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output on COBRA. The highest x-ray peak powers (300--500 GW) and total energy yields (6--10 kJ) were obtained using 4-mm-diameter arrays that stagnated before peak current. Additional findings include a decrease in soft x-ray radiation prior to stagnation as the initial wire spacing was changed from 1.6 mm to 785 $\mu$m, and a timing correlation between the onset of energetic electrons, hard x-ray generation, and the arrival of trailing current on axis---a correlation that is likely due to the formation of micro-pinches. The details of these and other findings are presented and discussed. In the second study, a new diagnostic setup was developed to record the visible-light spectra emitted from aluminum wire-array plasmas as a continuous function of time. To accomplish this, a half-meter Czerny-Turner spectrometer was used in conjunction with the existing visible light streak camera system. The emitted spectra was seen to consist solely of continuum radiation. This continuum data is now being used to determine electron density. To determine electron density from the continuum data, an absolute calibration of the detection system was required. The details of these experiments, and the absolute calibration technique are presented.
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