Supervisors: John Pasley (University of York), Luca Antonelli (First Light Fusion).
Inertial confinement fusion (ICF) is one of the possible approaches to releasing energy via nuclear fusion for power production applications. It requires deuterium-tritium fuel to be implosively compressed to thousands of times its initial density in a period of a few tens of nanoseconds. To attain such conditions a variety of implosion drivers can be employed, the most widely used of which are high power lasers. On December 5, 2022, an experiment at the U.S. National Ignition Facility released 3.15 MJ of fusion energy using a 2.05 MJ laser. This was the first time that a target gain of greater than one had been achieved in a lab-based fusion experiment [1]. This historic achievement was made possible using an approach to ICF called Central Ignition. In this approach the radius of the fuel capsule at peak compression is about 30 times smaller than its initial radius, and the maximum implosion velocity is between 300 and 400 km/s. In order to obtain a significant amount of burn by this approach, an exceptionally uniform compression is required. Even a small deviation from perfect uniformity in the driving pressure, or in the target structure, can lead to the target becoming unstable, preventing the development of the conditions necessary for nuclear fusion.
To mitigate the issues associated with Central Ignition’s high compression and implosion velocity requirements, this project will consider an alternative target design approach. This alternative approach is known as Volume Ignition, and it has been the topic of a number of previous studies over the last few decades [2-4]. It is also an approach of interest to First Light Fusion, who are partnering with the University of York to support this project. In the Volume Ignition approach, the fuel is confined by a thin, high atomic number (high-Z), shell. This high-Z shell is often referred to as the pusher. The pusher is itself surrounded by a set of nested shells of lower density that act to amplify the strength of the implosive shock wave launched by the driver. Having a high-Z shell surrounding the fuel reduces radiative cooling and serves as a reservoir of pressure to drive the fuel compression. In Volume Ignition, the required implosion velocity is lower than that of the Central Ignition scheme and it is possible that ignition may be more robust to imperfections in both the driver and target structure. It is for these reasons that we are interested to explore this approach further.
The behaviour of the pusher-fuel interface during the implosion remains a crucial issue, especially during the deceleration phase, when the pusher transfers part of its kinetic energy to the fuel. This is the moment at which this interface is most vulnerable to hydrodynamic instabilities. Hydrodynamic instabilities can exacerbate cooling of the fuel and prevent it from reaching the temperature and density required for ignition.
This project will consider some of the unresolved physics questions pertaining to Volume Ignition. These include its feasibility with alternative driver configurations and its susceptibility to hydrodynamic instabilities. The work will be performed using a combination of simulation-based studies complimented by the development of analytical models of target behaviour. These studies may underpin experimental work carried out both here in the UK, in collaboration with First Light Fusion, and overseas.
During the course of your studies, you will be encouraged to participate in workshops, conferences and summer schools. You will be working as part of a group which publishes regularly, and you will be actively supported in developing your scientific writing and publishing skills. You will also be supported in continuing your scientific adventures on completion of your studies – the most recent leavers from our group have gone on to postdoctoral research positions at Imperial College London, the University of California, the University of Rochester, and the University of Bordeaux.
Since this project is jointly funded by First Light Fusion you may, following discussion with your supervisors, decide to spend part of your time based down in Oxfordshire working on-site at First Light Fusion (up to one year, later on in your PhD).
This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.
This project is offered by University of York. For further information please contact: John Pasley (john.pasley@york.ac.uk).
[1] Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment, H. Abu-Shawareb, et al., Physical Review Letters, 132, 065102 (2024)
[2] Indirect-drive noncryogenic double-shell ignition targets for the National Ignition Facility: Design and analysis, P. Amendt, et al., Physics of Plasmas, 9, 2221-2233 (2002)
[3] Experimental study of energy transfer in double shell implosion, E. C. Merritt, et al., Physics of Plasmas, 26, 052702 (2019)
[4] Constraining computational modeling of indirect drive double shell capsule implosions using experiments, B. H. Haines, et al., Physics of Plasmas, 28, 032709 (2021).