Synergistic effects of neutrons and plasma on materials in fusion reactors & relaxation of merging magnetic flux ropes in fusion and solar plasmas

This thesis comprises of essentially two parts. The first deals with materials in a fusion reactor and examines how neutron damage affects material in a fusion reactor, with focus on how this is important for plasma damage. The methods used are neutron transport, primary event analysis and molecular dynamics. It found that the neutron damage by 14 MeV neutrons is restricted to back scatter events within the surface (first 20 microns). Molecular dynamics analysis showed that the issue of cascades is heavily dependent on direction of primary event and the energy of such. Statistical analysis was done to provide a standard approach for modelling of damage through neutrons. The second deals with the relaxation of magnetic flux ropes with an emphasis on kink unstable flux ropes. A relaxation model was developed which shows good approximation to simulation results of merging magnetic flux ropes. Subsequently, work was done to establish the physical processes involved in relaxation. This was done by examining magnetohydrodynamic (MHD) simulations of two flux ropes, one unstable and one stable. It was found that there is is a clear distance at which merger does not occur any more. Furthermore, a critical current seems to be a requirement at the edge a stable flux rope.