Application of X-ray Line Polarization to High-Energy-Density X-pinch Ne-like Mo Plasmas

Abstract

The search for high-yield, efficient x-ray sources is a leading goal in the field of High-Energy-Density (HED) plasma physics as x-rays are of critical importance to inertial confinement fusion, Z-pinch, and astrophysical plasmas. In this respect, Z-pinch plasmas are a primary contender. In particular, the X-pinch, which is a specific Z-pinch comprised of a wire load extending across an electrode gap and crossing at a single point, forming an X, is of prominent interest due to its production of a fixed-location dense plasma, thus simplifying diagnostic application. These plasmas are increasingly more studied as a viable laboratory x-ray source due to the intense x-ray (≥ 1.5 keV) bursts exhibited during the Z-pinch implosion. In this pursuit, the X-pinch is prime due to its high-density plasma production and fixed hotspot location, which allows for multi-spatially resolved spectral analysis. The X-pinch wire load also permits the study of multi-elemental plasma. For example, stainless steel alloy wires are analyzed for the astrophysically important Fe and Ni plasma spectral line emission. Moreover, X-pinches are experimentally observed to produce energetic electron beams with high likelihood, which, when coupled with spatially resolved diagnostics, allow us to confirm the presence of non-Maxwellian electrons. The polarization of x-rays can further diagnose physical characteristics of these plasmas. This x-ray line polarization is a formidable diagnostic in the detection of non-Maxwellian, suprathermal electrons, which have been shown to induce linearly polarized spectral emission through collisional processes with ions. This thesis intends to investigate the characteristics of these X-pinches through x-ray line polarization of Ne-like Molybdenum (Mo, Za=42) plasma. Theoretical tools involve non-local thermodynamic equilibrium (non-LTE) kinetic models to understand the collisional-radiative properties of both stainless steel and Mo HED plasmas. X-ray line polarization and spectral emission of a Mo X-pinch plasma are investigated through dual α-quartz (2d = 6.687 Å) crystal spectropolarimetry with axial and radial spatial resolution. In particular, polarization is evaluated through a comparative analysis of relative line intensities observed over a range of Ne-like Mo transitions. This thesis marks the first full comprehensive x-ray line polarization study of Ne-like Mo X-pinch plasmas.