Investigation of the Ablation and Implosion Phases in 1 MA Wire Array Z-Pinches with UV and X-ray Diagnostics
AuthorAnderson, Austin Alan
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Z pinches are a class of plasma configuration in which a large electrical current pulse magnetically compresses and confines a cylindrical plasma column. Z-Pinches are the most powerful laboratory producer of X-ray power and energy in the world. They are unstable and inhomogeneous plasma formation, and subject to strong instabilities. Plasma conditions during the ablation and implosion stages can determine the quality of the stagnating Z-Pinch and radioactive properties. New plasma diagnostics were fielded to study the ablation and implosion stages of the Z-Pinch. Experiments were performed using the 1 MA Zebra pulsed power generator and 50 TW Leopard laser at the Nevada Terawatt Facility and the University of Nevada, Reno. Ultraviolet (UV) laser diagnostics at the wavelength of 266 nm were applied to study the ablation and implosion stages of the wire array Z-Pinch. UV interferometry with an air-wedge differential interferometer was used to measures electron density during the ablation and implosion stage of a wire array Z-Pinch, and measured electron densities up to (1-3) x 1020 cm-3. Faraday rotation was used to measure magnetic fields and derive current distribution in the Z-Pinch during the ablation stage. X-ray imaging was also fielded to study the wire cores during the ablation stage. The high penetration of the X-rays allows the diagnostic to image the dense solid-liquid wire cores inside the ablating plasma columns in wire array Z-Pinches. Wire cores were backlit by silica He-α spectral line with a wavelength of 6.65 Å, and then imaging with a spherically bent quartz 1011 crystal. Fielding the X-ray imaging couple with UV shadowgraphy and interferometry allows for the study of Z-Pinch plasma in a wide range of electron density. X-ray absorption spectroscopy was used to study the electron temperature, ionization stage, and areal density of the plasma in Zebra-Leopard coupled shots. A single ray in aluminum star-like wire arrays was studied during the ablation stage. A samarium backlighting target was struck with the Leopard laser, producing a quasi-continuum emission of X-rays in the 8-9 Å range used for backlighting the wire ray. Two focusing conical spectrometers with mica crystals recorded absorption and reference spectra onto X-ray sensitive film. Absorption spectra was visible in the region of 8.2 - 8.4 Å. Electron temperature was determined using atomic kinetic codes and a two-temperature model of plasma.