Investigations of plasma evolution in Laser Ablation Z-Pinch Experiments using Time-Resolved Optical Spectroscopy
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Authors
Dutra, Eric C.
Issue Date
2019
Type
Dissertation
Language
Keywords
Magnetic field , Plasma , Spectroscopy , Zeeman , Z-pinch
Alternative Title
Abstract
Plasma is the most abundant form of visible matter in the universe. Plasmas make up approximately 99 percent of stellar objects observed including billions of stars and nebulae. High-energy-density (HED) physics is a rapidly growing area of physics that encompasses several disciplines including plasma-, condensed-matter-, nuclear- and astro-physics. Several important HED physics topics are currently active areas of research and include efforts to understand fundamental mechanisms driving magnetized plasma dynamics and radiative properties of magnetized plasmas. Experimental investigations aim to provide data needed to more accurately model details of the plasma evolution such as how currents flow within the plasma and how current symmetries affect magnetic fields. Plasma properties are usually determined from diagnostics that measure magnetic field strengths, photon emission and particle radiation, to name a few.In this dissertation, investigations of the temporal evolution of magnetically driven plasmas is presented. These studies were carried at the Nevada Terawatt Facility using the Zebra pulsed-power accelerator to magnetically compresses and confine a cylindrical plasma column. Important parameters needed to characterize these laboratory plasmas include magnetic field strength and orientation, as well as electron number density and temperature. To fully understand the characteristics of a plasma, accurate experimental measurement of these parameters is essential. To determine the electron temperature, the Boltzmann plot method was used. Simulated spectra from PrismSPECT where compared to experimental measurements in order to measure electron number density and temperature early in the pinched plasma formation. Simultaneously, Mach-Zehnder laser interferometry was used to provide complementary measurements of the electron number density. A novel method, streaked Zeeman-induced Magnetic Splitting (ZIMS) optical spectroscopy, was developed to measure time- and space-resolved magnetic field strengths in these hot, dense plasmas. This technique has also been applied to diagnose the magnetic field strengths in laser ablation Z-pinch experiments (LAZE), wherein a pulsed power driver pinches a laser ablated plume. To effectively utilize ZIMS, ionic plasma species were chosen such that the Zeeman splitting of different fine structure doublets occurs non-uniformly with increasing magnetic field strength in the plasma. A streak camera was then used to continuously observe spectroscopically resolved differential splitting from a well-defined spatial region in the plasma, and analysis of the measurements was used to determine non-directional magnetic field strengths with increasing plasma temperature and density. In parallel, we have developed a spectral line emission modeling code for ZIMS. The initial line shape parameters input into the code were varied to simulate emission spectra observed, and the fitting parameters were adjusted iteratively until an acceptable fit was achieved. These results were then used to infer magnetic fields strengths as a function of time and space in the magnetized plasma implosion. ZIMS results for a number of different LAZE target materials will be discussed.