Spectroscopic Measurements of Magnetic Field and Electron Density on Wire Array and Laser Plasmas
Magnetic field and electron density distributions within plasmas are crucial parameters in the study of high energy density laboratory plasmas. These measurements are challenging because often the magnetic fields undergo significant spatial and temporal fluctuations. Of the few measurement techniques possible, Zeeman splitting is the most promising option. However, this method has limitations when plasma conditions are such that line broadening due to the high plasma density and temperature surpasses the Zeeman splitting. The Zeeman broadening technique provides a solution to this field measurement problem by making simultaneous measurements of the widths of multiplet components. In this way, even if the splitting is not resolved, the difference in widths of multiplet lines provides an unambiguous field measurement. Additionally, through the Stark contribution to the line profile convolution, this technique offers estimates of the electron density. We have implemented this technique in magnetized laser plasmas and magnetized exploding wire array plasmas. We present spatially resolved magnetic field measurements from two different laboratory-produced plasmas using visible spectroscopy. We investigated the radial profiles of the magnetic field during the evolution of a plasma created by an intense laser pulse (I > 1014 W/cm2) that is allowed to expand in an azimuthal external magnetic field B < 40 T. We observed that the external field completely diffuses into the plasma after nearly 100 ns, but the field profiles in the plasma develop modulations that differ from the external field profile as the plasma continues to evolve. In wire array plasmas driven by the Zebra pulsed power generator (delivering 1 MA in 90 ns), we measured the radial electron density profiles and magnetic field distribution around the wires during ablation and in the precursor plasma. In these measurements the Zeeman splitting was not resolved, but the magnetic field strength may be measured from the difference between the widths of the line profiles. Space- and time-resolved measurements of magnetic field and electron density give insight into the dynamic behavior of these complicated systems. In this dissertation, we examine the strengths and limitations of this technique in different regimes and explore the feasibility of expanding this diagnostic beyond the plasma parameters observed in these experiments.
diagnostic, laser plasma, magnetic field, plasma, spectroscopy, wire array
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