Nano-scale Probing of Fusion Reactor Armour

New research by Trinity’s Felix Hofmann uses a new X-ray microscopy technique to examine nano-scale defects that can lead to material degradation in fusion reactors.

Fusion power promises an almost limitless, low carbon energy supply, which can help meet growing energy demands without contributing to the climate crisis. Fusion reactors will require protective armour inside the reactor vessel; these armour components will be exposed to extreme temperatures, very high heat flux and intense bombardment with ions and neutrons when in use. The neutron irradiation causes defects to form in the structure of reactor materials, which can dramatically degrade the properties of armour components. 

Unfortunately, most of these defects are too small to be seen using electron microscopy, the main method for observing material defects as small as a few atoms. But using X-ray beamline technology at the European Synchrotron Radiation Facility (ESRF), an international team of researchers including Felix Hofmann and colleagues have developed a new microscopy technique that allows the probing of these tiny imperfections at the scale of 1 billionth of a metre. The key result is that, for the first time, the new reconstruction approach allows taking imperfections of the illuminating X-ray beam into account and enables researchers to see more than ever before.

The authors applied this new microscopy technique, called Bragg Ptychography, to tungsten, the front runner material for fusion reactor armour. This allowed them to image in 3D the complex lattice distortions caused by helium injected into the lattice, which mimics the damage expected to form in armour components during fusion reactor operation.

Professor Hofmann notes, ‘Using Bragg Ptychography has finally allowed us to actually view in 3D how atomic scale crystal defects caused by helium ion irradiation are distributed within the tungsten matrix. Remarkably we found that fewer defects exist near grain boundaries, suggesting that perhaps nano-structured materials may offer better radiation resistance.

‘The 3D resolution of this technique has also uniquely enabled us to exclude unwanted artefacts at sample surfaces that are caused by sample preparation from our analysis. This is very important as it really allows us to pin down what defects are caused by the helium exposure. These new insights are key to developing new strategies for designing the next generation of radiation damage resistant materials.’

The research team included academics from Institut Fresnel, the Diamond Light Source, the Paul Scherrer Institute and the University of Oxford’s Department of Engineering.