X-ray spectroscopy of high temperature superconductors for understanding radiation damage mechanisms

Nuclear fusion reactors require high magnetic fields to confine the intensely hot plasma in which the deuterium/tritium reaction takes place.  The next generation of reactors rely on state-of-the-art high temperature superconductors (HTS) to achieve very high magnetic fields, the superconductor of choice being (RE)Ba2Cu3O7 (RE = rare earth element).  In operation in a fusion device, the HTS magnet windings will be exposed to high energy neutrons which cause severe degradation of the properties and eventually total loss of superconductivity long before any structural damage can be observed with atomic resolution electron microscopy.  This project will use polarisation-dependent high resolution x-ray absorption spectroscopy (XAS) to investigate the damage mechanisms in state-of-the-art superconductor samples.  XAS is a very sensitive probe capable of detecting irradiation induced changes in the local chemistry/electronic structure at the two different copper sites in the complicated unit cell which are very difficult to detect by other methods.  Initially, ion irradiation (e.g. protons, He+, O2+) will be used as a safe proxy for neutron damage, with the aim of progressing to neutron irradiated materials as proposed new handling facilities for radioactive samples become available on the beamline at Diamond Light Source.  In parallel with the experimental spectroscopy, the student will use cutting edge DFT modelling techniques to simulate the effect of structural defects on the spectra, enabling unprecedented insight into radiation damage as well as potentially shedding new light on the mechanisms of superconductivity in these complex materials.

Difference map of energy transfer and incident energy

Resonant X-ray Emission Spectroscopy (RXES) map showing the difference between He-irradiated and pristine GdBCO superconductor.

 

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