In this thesis visible spectroscopy is developed and used for two applications. Studies of motional Stark effect spectra for diagnosing the current distribution in the fusion plasmas with two different spectroscopic diagnostic systems: ratiometry and interferometry. Both systems provide non-invasive method for diagnosis of the internal plasma properties, e.g. magnetic field. Pitch angle of magnetic field lines are obtained from polarisation of Stark split Hα spectral lines emitted by energetic hydrogen atoms injected into the plasma volume by neutral beam. Several methods of calibration of the systems on TEXTOR and JET are discussed. The main result of this work is the first measurement of the safety factor radial profile with new ratiometric MSE system on TEXTOR. Studies of molecular fragmentation of free molecules CH4 and NH3 excited with synchrotron radiation by detection of the fluorescence from the fragments. The results give the decay path ways for the molecules when excited below the N and C ionisation edges. / QC 20101116

Steel is an important structural material in nuclear reactors used for example in pressure vessels and fast reactor cladding. In reactor environments it has been observed that ferritic steels are more resistant to swelling than the austenitic steels typically used. Much effort has been put into developing basic models of FeCr alloys which can serve as model alloys for describing ferritic steels. As a result, a number of interatomic potentials for Fe and FeCr alloys exist today. For the work in this thesis, basic material properties coming from experiments or ab initio calculations were used to fit interatomic potentials for Fe, Cr and FeCr implementing both the embedded atom method and the Finnis-Sinclair formalisms. The potentials were then validated by molecular dynamic calculations of material properties such as defect formation energies, migration energies and thermal expansion. Further studies of potential performance were carried out in simulations of radiation damage cascades and thermal aging. The influence of the interatomic potential on the primary defect state in materials under irradiation was analyzed in a study comparing results obtained using four different potentials. The objective of the study was to find correlations between potential properties and the primary damage state produced in simulations of displacement cascades. The defect evolution and clustering during different cascade stages were also investigated to try to gain a better understanding of these processes. / QC 20101208

QC 20101125

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