Study of Electron Collision with Free and Plasma Embedded Ions

Abstract

The present thesis is concerned with two aspect of the electron collision studies, one is of electron impact excitation (EIE) of highly charged Ge-like ions and highly charged barium ions and the other is for free as well as confined Mg+-ion in plasma environment. Study of EIE of highly charged Ge like ions in extreme ultraviolet (EUV) region of wavelength has great importance in many branches of research viz., astrophysics, fusion plasma studies, fusion devices, Electron Beam Ion Trap (EBIT). The lines observed in the EUV spectra reveal information about plasma characteristic viz., electron temperature, ion density and chemical composition. There is a great demand of structural, radiative and collision properties of these ions to understand the underlying processes in plasma. Highly charged Barium ions structural and collisional data in extreme ultraviolet region of wavelength has also drawn considerable interest due to critical role played in various areas of research such as in forming the saw-tooth waves in EBITˏ laser produced plasma exhibits the possibilities to become EUV source for the development of next generation lithography, understanding the excitation process of line emission for a variety of fieldsˏ including magnetic fusionˏ internal-confinement fusionˏ and astrophysics. With the ongoing ITER project, the need for atomic data for a wide range of As-like ions Ba23+-ion has become greater. Ions of Xe, Ba, and W have been identified of particular interest to fusion studies. In the estimation of the power loss from the impurities, atomic data are required for several parameters, such as energy levels, lifetimes, and radiative rates which is helpful in estimating the energy loss in fusion plasmas and modeling of astrophysical and laboratory plasmas. In controlled-fusion devices, the diagnosis of hot plasmas has great importance. Previously, very limited results have been reported for excitation cross section for such ions despite the great demand for plasma diagnosis purpose. Apart from these studies, electron collision with free as well as confined Mg+-ion in plasma environment has immense interest to a wide range of application in astrophysics and plasma physics. Precise atomic structure calculations are much important to study the plasma embedded atomic systems. Plasma environment not only alters the atomic properties of the system but also changes the excitation cross section. i The purpose of the present thesis is to provide the structure, radiative and collisional data for highly charged Ge-like and various charge states of barium, as these ions have great importance in many field of research viz., astrophysics, plasma physics, line identification in EBIT. The complete work of the thesis has been presented through five chapters which are describes as follows. Chapter – 1. This chapter introduces the complete thesis in brief. The detailed description of the relativistic distorted wave (RDW) method, which has been used in entire thesis to explain the electron collision with atom/ion on electron-atom collisions has been explained in detail. Finally, outlines of the thesis chapter wise. Chapter – 2. This chapter represents our study on electron impact excitation of dipole allowed transitions in the extreme ultraviolet range 8–55 nm for the germanium isoelectronic sequence Te20+–Cd16+. The fine structure transitions between the ground state having configuration 4s24p2 and the excited states with configurations 4s4p3 and 4s24p4d are considered for these ions. We adopted RDW method to calculate the excitation cross sections in the incident electron energy range from the excitation threshold to 5000 eV. To obtain the required ionic bound state wavefunctions we have used the multi-configuration Dirac-Fock (MCDF) method with correlations within the n = 5 complexes as well as performed relativistic configuration interaction calculations to include the quantum electrodynamic effects. The accuracy of these wave-functions is established by comparing our calculated wavelengths and oscillator strengths of the considered transitions with the previously reported measurements and other available theoretical results. We also provide the fitting parameters of the calculated cross sections and the excitation rate coefficients for their direct applications in plasma modeling.