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Development of UV Laser Probing Diagnostics for the Investigation of Dense Z Pinch Plasmas
AuthorAltemara, Sara Diane
AdvisorIvanov, Vladimir V
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UV, 266-nm wavelength, laser probing diagnostics were developed for the investigation of the dense plasma on the 1-MA pulsed power generator, Zebra, located at the University of Nevada, Reno. These new diagnostics complemented the 532-nm laser probing diagnostics, which were not highly applicable for a z-pinch with an electron density higher than 10^19 cm^-3, due to strong absorption and refraction of the beam as it passes through the plasma. The UV laser diagnostics, shadowgraphy and interferometry, have been successfully tested at the ablation, implosion, stagnation, and dissipation phases of wire-array z-pinches. Probing simultaneously with 266-nm and 532-nm light has shown that the UV laser probes deeper into the z-pinch plasma, with higher resolution. The UV laser probe enjoys a significant advantage over the 532-nm laser probe, because the inverse bremsstrahlung absorption increment and refraction in the plasma column is proportional to the wavelength squared. For interferometry, the phase shift of the laser beam is proportional to the wavelength. UV interferometry was employed to measure the plasma density profile up to an electron density of 1.2x10^20 cm^-3. A high resolution laser probing channel was developed for further study of the dense z-pinch plasma. Specially designed anode and cathode plates allowed installation of the objective lens inside of the vacuum chamber. A spatial resolution of 4 microns was achieved with UV. Instabilities in the dense plasma pinch were directly observed. The micro-structure of the dense pinch was unfolded for the first time. Micro-pinches, small-scale and mid-scale instabilities, large kink and sausage instabilities, and breaks in the plasma column were studied with UV high resolution shadowgraphy and interferometry. To investigate the dynamics of the dense plasma, a second, time-delayed, frame was developed for the UV laser diagnostics. Large velocities, greater than 100 km/s, were measured. These demonstrate the generation of kinetic energy in the stagnation phase of the z-pinch.