Theoretical and Experimental Studies of Radiation from High-Z Multiply Ionized L-shell Ions with Emphasis on X-ray Line Polarization

High-Z multiply ionized atoms have an intrinsically complicated nature. As such, the atomic physics associated with them, and corresponding application to high-energy-density (HED) plasmas is a complex and intricate problem. This dissertation intends to help in addressing this problem by providing a detailed theoretical and experimental study of radiation from high-Z multiply ionized ions that are influenced by a diverse set of atomic processes. The implemented theoretical tools include relativistic atomic structure codes, to generate atomic databases and calculate x-ray line polarization, as well as non-local thermodynamic equilibrium kinetic modeling, which is used to understand the radiative properties of HED plasmas. The Electron Beam Ion Trap (EBIT) and a few HED plasma facilities are utilized along with an advanced set of diagnostics. The HED plasma diagnostics include: x-ray spatially-resolved spectrometers and pinhole cameras, fast x-ray diodes, and an optical laser shadowgraphy system. Three primary objectives are addressed using these theoretical and experimental tools. First, a study of the line emission and x-ray line polarization of multiply ionized Molybdenum (Mo) ions is accomplished. Polarization-sensitive experiments were carried out on the Lawrence Livermore National Laboratory EBIT to measure the degree of polarization of several electric dipole and forbidden quadrupole transitions in Ne-like Mo ions. The well controlled conditions and almost monoenergetic electron beam of an EBIT provide a unique opportunity for the benchmarking of theoretical calculations, including x-ray line polarization. The measured degrees of polarization show excellent agreement with calculations from the fully relativistic Flexible Atomic Code. Next, the theoretical and experimental studies of L-shell Silver (Ag) plasmas as some of the most efficient L-shell Z-pinch radiators started with calculating theoretical L-shell Ag spectra influenced by dielectronic recombination (DR), and then expanding to applications to HED Ag plasmas. Detailed theoretical calculations of the DR satellite lines in Na-like Ag ions are necessary in order to further explore this important atomic process for HED plasmas. This study is complemented with a spectroscopic analysis of L-shell Ag spectra from X-pinches. The high electron temperature, density, and compact plasma source signatures of X-pinches are especially useful for HED plasma spectroscopy and x-ray line spectropolarimetry. The X-pinch experimental data are produced on the Nevada Terawatt Facility (NTF) Zebra generator at the University of Nevada, Reno. Spectroscopic analysis reveals the existence of two distinct plasma radiation sources, one which originates from the cross point and produces electron temperatures as high as 1900 eV, and a much colder region interacting with a highly energetic electron beam. Lastly, an investigation of the radiative properties of K-shell Argon (Ar) and L-shell Krypton (Kr) HED plasmas produced by a dense plasma focus device in Singapore, and laser-irradiated gas-puffs on the Leopard laser at the NTF, are presented and compared. The experimental results are used to benchmark two new non-LTE kinetic models for Ar and Kr, to reveal the presence of electron beams in plasmas, and to identify the best candidates for future x-ray spectropolarimetry studies with noble gas HED plasmas