Nuclear fusion reactor materials: modelling atomic-scale irradiation damage in metal

Achieving nuclear fusion as an energy source on Earth is a practical goal that relies on continuing scientific and engineering innovation. Functional fusion reactors around the world today allow scientists and engineers to plan improvements that will eventually allow for greater energy output than the input required to operate the machine (including heating the plasma and operating the superconducting electromagnets that confine the plasma, among other energy inputs). The fusion reaction between nuclei of hydrogen isotopes is a carbon-free source of massive amounts of energy that could be paramount in a global turn towards greener energy. The fusion fuel needed to provide one person’s energy use for 100 years (assuming 20 kWh per day) is contained within roughly one and a half bathtubs of water and 3 laptop batteries. Given the enormous payoff of fusion, continued research and development are of great interest so that current challenges of heating and confining plasma, mitigating plasma disruptions, improving efficiency of magnets, and extending the lifetime of materials subjected to the harsh conditions surrounding the plasma may be overcome. Fusion reactor materials research carried out here at the BSC contributes to this ambitious goal. The idealistic goal for fusion materials research is to provide predictions about material behavior with the accuracy of quantum mechanical calculations at the scale of a full fusion reactor. Using strategic approximations and working at a small scale, computational fusion materials researchers can accurately reproduce and explain experimentally observed physical phenomena, such as the formation of microstructural defects in metals under neutron-irradiation, and offer the best predictions available for behavior of materials in future fusion reactor environments, where data about what will happen simply do not exist yet. In the study presented here, we examined the thermal conductivity, or how quickly a material allows heat to flow, of tungsten (W). W has been selected for plasma-facing components in ITER, which is currently under construction. We used LAMMPS atomic modelling of materials software and found that the thermal conductivity of W is significantly decreased in the presence of defects

Fold Lens Flux Anomalies: A Geometric Approach

We develop a new approach for studying flux anomalies in quadruply-imaged fold lens systems. We show that in the absence of substructure, microlensing, or differential absorption, the expected flux ratios of a fold pair can be tightly constrained using only geometric arguments. We apply this technique to 11 known quadruple lens systems in the radio and infrared, and compare our estimates to the Monte Carlo based results of Keeton, Gaudi, and Petters. We show that a robust estimate for a flux ratio from a smoothly varying potential can be found, and at long wavelengths those lenses deviating from from this ratio almost certainly contain significant substructure.Comment: 16 pages, including 8 figure