Degradation of thermal conductivity in tungsten alloys under irradiation

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Tungsten-based alloys are currently the principal candidates for plasma facing components in fusion reactors due to their unique combination of properties such as neutron irradiation resistance, low sputtering yield, good high-temperature strength and thermal conductivity. The relatively high ductile-to-brittle transition temperature of tungsten, which even increases under neutron irradiation, is one of the main problems of using tungsten as plasma-facing material. Alloying tungsten with elements such as Ti, V or Ta improves the material's ductility. Unfortunately, our limited neutron irradiation data proves the degradation in thermal properties of pure W, and the effect of irradiation in thermal performance of those alloys remains unexplored. Changes in thermal conductivity due to irradiation damage is one of the more pressing areas of information required for the deployment of fusion reactor technology. The aim of the project is to detect changes in thermal conductivity in irradiated tungsten-based alloys, and to correlate those changes in conductivity to the lattice defects induced by radiation fields simulating those expected in the proximity of the hot plasma in fusion reactors. This project involves the use of intense ion beams to simulate the neutron damage that W alloys will be experiencing in future reactor conditions. Ion irradiation allows us to achieve the damage doses that will be experienced inside the reactor after several years of operation. The student will characterise the damaged areas of the material at the atomic-to-nanometer scale using advanced analytical electron microscopy and positron annihilation spectroscopy. The nature and concentration of radiation-induced lattice defects, such as dislocation loops or voids, will be correlated with variations in thermal conductivity. The student will have opportunities to learn fundamental radiation damage mechanisms to nuclear materials at an advanced level, to use upfront particle accelerators at large scale international user facilities, and to become an advanced user of electron and positron probe techniques.