Fusion Materials

Material Physics

Fusion reactors require very high temperatures and pressures. Materials CollisionsThe fusion plasma is extremely hots and active.  Whilst the magnetic field is designed to keep the plasma separated from the wall of the reactor this is not always possible and the plasma, or active particles from the plasma, may impact the walls of a fusion tokamak.  For sustainable fusion energy reactors will need to have a lifetime of many years and be active for most of that lifetime.  Therefore, the materials that the reactor is built from must be able to withstand the likely impacts and damage that fusion plasmas will inflict on them.

Reproducing the actual conditions of extended high neutron flux (as materials encounter in a fusion reactor) is currently impossible in the laboratory.  Consequently materials tests will require extrapolations from experiments conducted under alternate irradiation conditions.  Since radiation damage is a non-equilibrium process, there is no simple analytic way to carry out such extrapolations.  Thus a detailed understanding of the fundamental processes involved is required, and this can only be obtained from simulation and full understand of the processes involved in irradiation damage at the atomic level.  At the most ambitious level, this will enable design of radation-resistant materials. Even at a more prosaic level it will enable us to build models based on low-dose, short timescale experiments for reliable exploration of longer term effects.

Computational simulation of materials to understand the demands of fusion reactors and the likely impact on those materials is therefore essential to ensure that the correct materials are used for the construction of the reactors and therefore that the reactors have adequate lifespans.

At present, stainless steels are by far the most likely materials to be used in the construction of fusion reactors.  However, there is some evidence that ferritic (bcc) steel has better self-healing properties, albeit with a reduction in the structural behaviour at high temperatures.  The main causes of radiation damage in steels are corrosion, swelling, creep, precipitation and grain boundary segregation.  All of these are relatively slow processes and therefore to perform accurate calculations for processes will require simulation Damage of Copper by Argonof years of material time.  A typical 250-atom quantum calculation of impurity interaction in steel might take an day of supercomputer time.  Typical commercial steel may have ten elements, each of whose interactions with each other, and with vacancies, interstitials helium and other defects should be considered. Early results suggest that these interactions may not be linearly additive, so the combinations quickly become intractable.  It is evident that to model the physics required to understand radiation damage to metals over the large time scales required for damage to become evident will require very large amounts of computational resources.