XFEL studies for laser fusion: generating accurate information-rich data sets for code benchmarking and validation (plasma strand project)

Supervisor/s – Nigel Woolsey (University of York)

Inertial fusion energy is a grand challenge undertaking for humankind requiring innovation, experiments, and the development of predictive modelling to accelerate the development of inertial fusion as a ‘clean’ source of power. The inertial fusion concept uses lasers either indirectly or directly to rapidly ablate a spherical capsule containing deuterium–tritium (DT) driving the DT with sufficient kinetic energy to initial thermonuclear fusion in a hotspot and sustain fusion-burn in the surrounding dense shell. As the ultimate goal is energy gain, of the two approaches to implode a spherical capsule, direct drive is more attractive. This is because direct drive laser-energy coupling to an imploding target is potentially more efficient.

There are challenges as the spatial and temporal coherence of the lasers result in interference patterns on the capsule spoiling the symmetry and uniformity needed to compress the capsule. These interference speckles transfer or “imprint” drive perturbations within the ablating plasma. This modulates the pressure at the ablation surface and at the inward moving shocks seeding the Richtmyer-Meshkov and Rayleigh-Taylor instability. As the implosion proceeds, the Rayleigh-Taylor instability grows and risks destroying the imploding shell. In addition, the laser speckles excite laser-plasma instabilities, these are detrimental as they reduce the drive available for the implosion, generate high-energy electrons that preheat the target and can result in the energy exchanging from one beam to another spoiling the symmetry of the drive.

This project will use extremely intense X-ray flashes from the European XFEL as a high accuracy X-ray imager for laser driven experiments to measure the early time laser-target interaction, target material response, and the seeding of Richtmyer-Meshkov and Rayleigh-Taylor instabilities. XFEL stands for X-ray Free Electron Laser. The European XFEL supports repeat measurement and gathering of information that will enable benchmarking of simulations with unprecedented accuracy and detail. XFELs have exceptional spatial resolution and potential to reach < 1 μm. Direct imaging includes absorption-contrast imaging similar to a hospital X-ray yet when coupled with the coherent properties of the XFEL, phase-contrast imaging enables interface and steep density gradient tracking. Moreover, we will explore the use of XFEL with lithium fluoride detector to attain sub-micron resolution and the opportunity to characterize all seeds for hydrodynamic instabilities, this includes the presence of pre-existing and dynamically formed microstructures. Inverse imaging, for example using small-angle-X-ray-scatter (SAXS), offers a unique way of measuring with exceptional spatial and temporal resolution distributions of electron density within the target and through energy tuning XFEL wavelength measure the plasma opacity.

In this project, you will exploit the European XFEL and DiPOLE, and other facilities such as SACLA and LCLS-II, to gather data important to laser fusion and data-mine the measurements using computational analysis tools in development at York. These measurements will feed into larger inertial fusion collaborations within the UK, Europe and the USA giving the student opportunities to model experiments with cutting-edge computational models.

The project will be mainly based in York and offers opportunities to travel to XFEL and laser-plasma facilities in Europe.

This project is offered by The University of York. For further information please contact: Nigel Woolsey nigel.woolsey@york.ac.uk

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