A number of challenges are faced by developers of fusion energy, one of these being the fusion reactor layout and the structural materials from which it is built. These reactor wall materials also carry out the important job of ensuring that the fusion plasma is safely confined. The inner most wall in the reactor is known as the Plasma-Facing Material (PFM) and has to be designed to withstand plasma strikes and also act as a heat sink for the intense radiation produced during fusion. Factors such as contamination. durability, thermal and electrical conductivity must be taken into consideration when selecting a PFM. Materials such as tungsten, beryllium and carbon-graphite materials have been used up until this point.
This research project is aligned with the EPSRC's Energy Theme and aims to evaluate the use of isotopically pure, CVD diamond (single crystal and polycrystalline) and Graphene on diamond structures as a PFM.
One of the challenges with existing PFM materials is their chemical stability and the risk of the materials eroded from the reactor wall adversely affecting the operation of the fusion reactor. Carbon-based wall materials have been used in the past but the loss of thermal conductivity under energetic plasma particle bombardment and absorption of the fuel gases has proven problematic. For synthetic diamond this has also been viewed as an issue that needs to be resolved even though its use is favourable due to it being a light element that has less influence on fusion plasma operation. This project will explore new approaches for improving the resilience of diamond to the fusion plasma environment and its operation as a PFM. This will include the infusion of diamond with high loadings of hydrogen isotopes to limit tritium absorption, incorporation of high concentrations of boron and the use of graphene to localise/limit tritium fuel gas retention. High quality, thermally and electrically conductive diamond structures will be synthesised by chemical vapour deposition in the Bristol Diamond Laboratory, and their physical and electrical properties will be characterised using material analysis facilities at Bristol(NanoESCA, SIMS,XRT,HSAFM) and the Materials Research Facility(MRF) at Culham. Candidate diamond PFM structures will be evaluated experimentally by neutron and H,D,T irradiations to simulate PFM operation using facilities at Culham in the interim H3AT facilities, and the Divertor Science Facility. To support experimental work, model calculations using LAMMPS and MCNP will be conducted in collaboration with UKAEA personnel. It is anticipated that the student will be seconded to UKAEA for at least 8 weeks each year to participate in experimental campaigns and UKAEA-sponsored PhD training activities.