High Temperature Superconductors for Fusion Technologies

Lead Research Organisation: University of Oxford
Department Name: Materials

Abstract

Nuclear fusion - the joining together of atomic nuclei of light elements such as hydrogen to form larger nuclei - is the process by which vast amounts of energy is produced in stars like our sun. If it can be harnessed on Earth it has the potential deliver a nearly unlimited and safe source of energy which does not produce the environmentally damaging CO2 emissions that are released by burning traditional fossil fuels. However, for nuclear fusion to occur, extremely high temperatures and pressures are required because positively charged atomic nuclei within a plasma have to collide with each other with sufficient energy to overcome the immensely strong electrostatic repulsion forces. To achieve nuclear fusion in a machine on Earth, extraordinarily high temperatures of around 150 million degrees Celsius are needed, about 10 times higher than the temperature of the sun's core. This precludes the use of traditional materials to confine the plasma, and in the most common type of fusion reactor called a tokamak, strong magnetic fields are used instead. Since the power density of a particular geometry of tokamak scales with the strength of the magnetic field to the power of four, there is a huge benefit to using higher field magnets for plasma confinement.

High temperature superconductors - materials that can conduct electricity without any resistance - are an enabling technology for a new generation of compact nuclear fusion reactors that are widely believed will open the door to commercialisation of fusion for energy generation. This is because state-of-the-art high temperature superconducting tapes can carry extremely high electrical currents, even when subjected to enormous magnetic fields that completely destroy superconductivity in the best low temperature superconductors. However, although high temperature superconducting materials with fantastic properties are now available in lengths up to about 1 km in the form of flexible tapes known as coated conductors, the materials are incredibly complex and sensitive to damage, making their practical deployment in magnets for fusion devices a major challenge.

This programme of research involves using a unique combination of advanced materials characterisation and modelling techniques to determine how high temperature superconductors will degrade in the harsh environment of a fusion reactor where they will be continually bombarded by high energy neutrons. The focus will be on understanding the underlying damage and recovery mechanisms in these complex functional ceramics under the most realistic conditions possible. Since in operation the superconductors will be irradiated by neutrons whilst in their superconducting state at cryogenic temperatures, innovative in situ experiments will be performed to understand the differences between room temperature and low temperature radiation damage. The experimental programme will be supported by first principles modelling of pristine and defect structures in the superconducting compounds, and the outcomes will be used to validate larger scale simulations of radiation damage as well as providing key data on degradation to feed into materials selection and magnet design decisions for the next generation of fusion magnets. The advanced characterisation methodologies developed in this fellowship will also be applied to understanding radiation damage in a wider range of fusion relevant materials.

Publications

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