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Title: Using scanning electron microscopy (SEM) and transmission electron nncroscopy
Author: McKeown, Karen
Awarding Body: Queen's University of Belfast
Current Institution: Queen's University Belfast
Date of Award: 2008
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Electron impact excitation collisions are important processes for spectral line formation of plasmas. The work undertaken in this thesis focuses on such collisions involving Li-like ions, important in both astrophysical and magnetically confined plasmas. By having reliable atomic and collisional data, such as energy levels, radiative rates and excitation rate coefficients, it is possible to generate models to describe such plasmas. The atomic data were calculated using the General-Purpose Relativistic Structure Program (GRASP; Dyall et al 1989), for several Li-like ions, namely S XIV, Ar XVI, Ca XVIII, Ti XX, Cr XXII, Fe XXIV and Ni XXVI. Including relativistic effects in the calculations leads to the generation of 24 fine-structure energy levels when orbitals with 11,/ =:; 5 are considered. Oscillator strengths, were generated for all 276 transitions arising amongst these levels when maintaining a frozen core of Is2 • Comparisons were made with both theoretical and experimental data available from the publications of Nahar & Pradhan (1999), Nahar (2002), Whiteford et al (2002) and Del Zanna (2006), along with NIST data. Collisional calculations were performed for Fe XXIV, an abundant ion in solar and fusion plasmas, which has the potential to be employed in photo-pumping schemes for X-ray lasers. The calculations were performed using the Dirac Atomic Relativistic Code (DARC; Ait-Tahar, Grant & Norrington 1996), which is a fully relativistic code based on R-matrix theory. In addition to carrying out these calculations, DARC was further developed to provide a solution to the problem of convergence which affects optically allowed transitions in the above threshold energy region. Comparison of these results was made with data already available in the literature, with discrepancies being highlighted and discussed. The work of Berrington & Tully (1997) did not include the n=5 orbital, and comparisons with the results presented here showed how important these are for low temperatures. Discrepancies between this work and that of Whiteford et al (2002) were also identified. Despite being given access to their unpublished data, the source of the identified discrepancies remains elusive. The problems identified require further investigation which lies beyond the scope and resources of the present work.
Supervisor: Not available Sponsor: Not available
Qualification Name: Queen's University of Belfast, 2008 Qualification Level: Doctoral
EThOS ID:  DOI: Not available