Fusion demands a balance between heating a deuterium-tritium plasma to the necessary thermonuclear temperatures whilst confining the plasma for long enough that a large fraction of the deuterium-tritium fuel undergoes fusion. Inertial confinement fusion (ICF) uses many lasers to ionize and ablate the surface of a capsule containing the fuel with the ablation of the outer surface driving spherical compression of the core to very high densities over a short period of time before igniting a thermonuclear burn. A number of problems degrade the efficiency during the compression of the capsule reducing the pressure and temperature of the core, preventing ignition. A common problem is that the capsule does not implode symmetrically. A great deal of effort is devoted to ensuring and measuring the symmetry of a capsule during the compression and ‘stagnation’ phases of an implosion. Imaging measurements take advantage of the x-ray, gamma ray and neutron emission from the plasma.
This project focuses on developing new imaging techniques to measure the symmetry of an imploding fusion capsule. Our initial ideas are to develop x-ray phase contrast imaging to understand what advantages the technique offers. This will require detailed computation studies using two- and three-dimensional implosion simulations and the creation and the then interpretation of synthetic phase contrast images.
In this CDT project, you will work on complementary approaches to use secondary x-ray source, or backlighters, to radiograph the capsule and record the x-ray attenuation on a time resolving detector. Here, we will use this approach and combine it with phase shift measurements that results from x-ray’s passing through different parts of the capsule. The phase shift is inferred from spatial variations in intensity resulting from interference between diffracted and undiffracted waves. This is particularly important for ICF experiments, as phase contrast imaging is more sensitive to density variations with target dominated by low atomic number elements than conventional attenuation-based x-ray imaging. Three or more line of sights are needed to enable three dimensional image reconstructions.
We will design phase contrast imaging techniques for direct-drive shock ignition experiments, as part of a large international project that involves teams in France and USA. The shock ignition approach to ICF separates the compression of the fuel from the process raising the fuel temperature to initiate nuclear fusion burn. In this scheme a strong shock is launched late in the compression phase and the collision of shocks close to the compressed capsule centre rapidly raises the temperature to start ignition. Our aim is to the phase contrast imaging to study the symmetry of the shocks before and during collision.
This project will be based at STFC following an initial training period at York. The project offers many opportunities to travel for collaborative meetings, to some experiments and conferences.
Skills that the student would learn during the PhD include:
• Work with a diverse technical and scientific team across a number of cultural regions • Build effective communication skills and networking. • Acquire formal communication skills through poster and oral presentations at conferences and the writing of reports and papers. • Develop inertial fusion diagnostic and data analysis expertise. • Develop detailed knowledge of multi-dimensional inertial fusion modeling.
This project is offered by University of York. For further information please contact Prof. Nigel Woolsey at: [email protected] and send a short email outlining your interest in this project.