ATOMIC STRUCTURE STUDIES OF SPECIES RELEVANT TO ASTROPHYSICAL AND FUSION PLASMA

Abstract

This thesis explores the fundamental structure and radiative properties of atoms(ions) relevant to astrophysical and fusion plasma. It investigates the complex interactions among atomic electrons, the interaction of atomic electrons with the nucleus, and external magnetic fields. Additionally, it examines how atomic systems interact with free electrons, providing essential insights for analyzing laboratory and astrophysical spectra. In particular, the electron impact excitation (EIE) process, where the EIE cross-sections and the corresponding rate coefficients are studied. These parameters are essential for plasma modeling and diagnosis. Therefore, in this thesis, these atomic structural, radiative and collisional parameters are investigated for a wide variety of atomic species, which we divide into three broad categories. The first category focuses on highly charged ions (HCIs), subdivided into two main groups. The first group consists of inert gases, viz., argon, krypton, and xenon, which are suitable for use as seeded impurities in fusion plasma. These gases are valuable diagnostic tools for studying plasma properties. The second group comprise HCI of an element produced by various nucleosynthesis processes and is important for astrophysical studies. In high plasma temperatures of magnetic fusion reactors like the International Thermonuclear Experimental Reactor (ITER) and China Fusion Engineering Test Reactor (CFETR), inert impurity gasses can be found in all possible ionic states. For diagnostics and modelling of such plasma, atomic data for all the ionic states of impurity ions is required. However, there is a major scarcity of their atomic data. Hence, the thesis deals with fully relativistic calculations of energies, radiative parameters and hyperfine structure (HFS) constants, isotope shifts (IS), and EIE cross sections for a few selected HCIs of Ar, Kr and Xe, with a special focus on Xe. The thesis further provides detailed atomic fine and HFS of Sc ion. The presence of Sc in various astronomical environments, including stellar atmospheres, white dwarfs, disc and metal-rich halo stars and metal-poor stars, motivated this investigation. Its atomic data for all the ionization stages is required for the correct spectral interpretation of metal-poor stars.