The plasma-facing components and breeding blanket of any future fusion tokamak will be subjected to one of the most extreme engineering environments possible. Materials will experience temperatures of up to 1200C in steady state and 3300C in transient events, and irradiation with 14MeV neutrons, causing displacement damage, transmutation giving rise to compositional changes, and internal H and He generation, plasma facing surfaces also can have high erosion rates due to interactions with the fusion plasma. Ideally, the materials should not retain tritium or themselves transmute to long-lived radioactive isotopes. For fusion to be feasible as an economic power source, the materials must be able to survive these conditions, retaining usable thermal and mechanical properties, for five years or more.
Materials of current interest include special “reduced activation” steels, tungsten alloys and composites, molybdenum alloys, copper alloys and silicon carbide.
Current and future research projects investigate the processing, joining, microstructure, mechanical properties, and resistance to radiation damage of these materials. Research projects in fusion materials generally use a range of specialised research techniques:
- advanced processing, coating and joining methods (mechanical alloying, rapid solidification, spray forming, additive manufacture, friction-stir welding)
- irradiation of materials by high-energy ion-beams, protons and neutrons.
- cryogenic, high-magnetic-field measurements on superconducting materials.
- transmission electron microscopy (TEM), including in-situ irradiation, and field-ion microscopy (FIM) of radiation damage processes.
- microanalysis of microstructural effcts from radiation by atom-probe tomography (APT) and electron-optical methods.
- X-ray diffraction including use of the Diamond Light Sourc.
- mechanical testing, particularly using new micromechanical techniques, over a wide temperature range.
- computer modelling of radiation damage effects, deformation and microstructural development.
A CDT student’s research project will usually use several of these techniques in combination to address a technologically-important issue; for example using APT of specially irradiated tungsten alloys to see how radaition changes the distribution of atomic types, and micromechanics to investiaget how that changes the alloys’ mechanical properties; or TEM and APT of “home made” dispersion-strengthed steels to track how their microstructure develops during processing; or in-situ TEM to study the evolution of radiation damage structures at high (reactor) temperatures, coupled with computer modelling of dislocation -defect interactions.