Dynamic X-ray diffraction and imaging of shocked solids
The behaviour of materials under extreme dynamic compressions is usually studied through bulk measurements, such as macroscopic material/wave motion or average total strain. From these measures, the thermodynamic state at high pressure and temperature are calculated, and assumed to describe a uniform, equilibrated state. In order to reveal finer details regarding the initial stages of compression, specifically the early motion of the lattice during loading, new diagnostic techniques capable of penetrating deeply into a deforming solid must be pursued. The ISP has recently developed a new UK capability for performing X-ray imaging of dynamic conditions using a portable gas launcher at the Diamond Light Source. This work is currently pursuing full-field imaging of the development and growth of mesoscopic defects, however its quantitative translation into local lattice strain or phase identification remains limited. Such information can be gained by probing in reciprocal space, requiring a new capability to perform dynamic X-ray diffraction.
This PhD project will focus on enhancing dynamic X-ray techniques by incorporating diffraction measurements on a variety of shock and ramp compressed material experiments, providing a quantitative measurement of lattice structure throughout a number of high pressure phenomena (e.g. elastic-plastic behaviour, structural phase transitions, high pressure chemistry). In addition to experiments at the Diamond Light Source, this work will also utilise the new long-pulse laser shock extension of the Cerberus laser (using many ex-Helen components), and new high intensity, multi-KV X-ray sources currently being explored by an AWE CASE student. By applying intense pressures to material samples using either the mesoscale gas launcher (10s of GPa) or the long-pulse laser (100s of GPa), both Bragg and Laue scattering geometries, and their sensitivity to structural phenomena, will be studied. Coupled with advanced surface-based diagnostics (1D-line and 2D-imaging velocimetry), this project will strengthen the link between bulk observed behaviour and the underlying crystal structure.