Exploiting high repetition rate experiments in dynamic high-pressure physics (plasma strand project)

Supervisor/s: Andy Higginbotham (University of York)

Dynamically driven high-pressure experiments allow us to reach pressure and temperature regimes inaccessible to traditional static compression platforms.  These dynamic approaches allow us to recreate the conditions at the cores of planets or to search for new metastable polymorphs of solids which might possess technologically unique properties.

The behaviour of material in the multi-megabar regime is still only partially understood.  This is due to the fact that materials at megabar pressures have a stress-strain energy density comparable to the typical energy density of chemical bonds.  This fundamentally disrupts bonding processes and leads to a new, richer chemistry at high pressure.  In a subset of cases, these high-pressure materials remain stable upon release to atmospheric conditions.  For example, the extreme strength of diamond, a high-pressure allotrope of carbon, can be directly related to the change in bonding caused by the high-pressure environment of the Earth’s mantle.  Recent work has also demonstrated the possibility of creating high temperature superconductors at megabar pressures, but a path to recovery of such material is still being sought.

Dynamic approaches also give us insight into inherently dynamic processes, such as cratering, confinement of debris during jet engine failure or behaviour of ablator material during inertial confinement fusion experiments.

The extreme conditions and transient nature of these dynamically created states makes experiments in this area exceptionally challenging.  Laser drivers are used to ablate the surface of the sample of interest, with the expanding plasma plume generated launching a compression wave into the undisturbed solid material ahead.  These experiments require laser drivers with at least 100’s (up to tens of thousands) of joules of laser energy to produce compressions strong enough to reach the megabar pressure regimes of interest.  Moreover, these lasers operate at nanosecond-scale pulse lengths, giving a limited window of opportunity to probe the resulting high-pressure state with structural probes such as x-ray diffraction before the sample decompresses.

Until very recently experiments such as these were restricted to sub-Hz repetition rate due to limitations on the technology of the driving laser and x-ray sources.  This has now changed, with facilities coming online in 2022 with 10Hz repetition rate in both the optical and x-ray components.  We expect this to transform our experiments, moving us from a mode where only a handful of useful shots might be achieved in a week-long experiment, to one where many 10’s of thousands can be captured in just a day.

There is clear opportunity here to revolutionise the field.   We will be able to scan parameter space widely, searching, for example, for routes to recovery of new metastable materials.  Or, we can develop detailed understanding of how varying compression pathway affects material deformation, and thus better understand the early stages of ICF capsule compression or jet engine failure.

In this PhD you will explore how to handle these new, enlarged data sets.  You will develop techniques, including machine learning-based approaches, to categorise and analyse data sets too expansive for shot-by-shot analysis.  Furthermore, you will look at what new physics we can explore given the richer, more complete data sets provided by high repetition rate experiments.  You will develop an understanding of how evaluate subtle features in the data which are often ignored in single-shot data, but could be interpreted in this rich data set to understand the details of material plasticity, phase transition, and failure.

This PhD is expected to be a combination of experimental work at X-ray Free Electron Laser facilities, such as the European XFEL at Hamburg, and computational analysis of data sets. You will work as part of international collaborations with world leading groups in countries including the UK, US, and Germany.

This project is offered by University of York. For further information please contact Dr Andy Higginbotham (Andrew.higginbotham@york.ac.uk).

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.