OxCHEDS research themes
The spectrum of research carried out at OxCHEDS can be sorted into seven interrelated topics: plasma accelerators, laboratory astrophysics, inertial fusion energy, high-field physics, matter at planetary pressures, dynamic compression of solids, and machine learning applied to HED science. A brief summary of the seven aspects of the OxCHEDS research portfolio may be found below, along with links to the relevant academics' pages and those of their individual research groups.
When an extremely intense laser pulse is sent through a low-density plasma, it blasts electrons out of its way via a mechanism called the ponderomotive force, and thus leaves in its wake a bubble of positively-charged plasma. As electrons rush back in to fill the bubble, they are accelerated to energies rivalling those that can be achieved via conventional (kilometre-long) particle accelerators over distances of just a few millimetres. Such plasma accelerators could provide compact sources of extremely energetic particles, having applications in both fundamental scientific research and in biological, physical, and medical sciences. Read more about plasma accelerators here.
The astrophysical world is filled with exotic states of matter and physical processes unlike anything encountered on Earth: gas giants and white dwarfs harbour ultra-dense cores contained by massive gravitational forces; stars die spectacularly in supernova explosions driven by runaway nuclear fusion; and turbulent plasmas in remote galaxy clusters whir away generating the magnetic fields that pervade the Universe. These phenomena can now be brought into the laboratory with the aid of high-power lasers, which can create plasmas with properties akin to those encountered in astrophysical scenarios. Read more about the field of ‘laboratory astrophysics’ here.
Inertial fusion energy
Nuclear fusion would provide an energy source that is clean, safe, and (virtually) inexhaustible. To initiate the kind of fusion processes that power stars here on Earth is extremely challenging, however, and requires that thermonuclear fuel be heated to millions of degrees while remaining contained long enough for fusion to occur. This can be achieved via inertial confinement fusion (ICF), in which a small pellet of deuterium-tritium fuel is fired upon from all sides simultaneously by an ensemble of high-power lasers. These efforts are conducted at international high-power-laser facilities, such as the National Ignition Facility (NIF). Read more about inertial fusion here.
At the very highest intensities attainable with modern high-power lasers systems (> 1018 W cm-2), it is now possible to access the so-called relativistic plasma regime, in which a plethora of exotic physical processes are expected to take place. For example, it is possible in this regime to generate matter directly from light via the Breit-Wheeler process, whereby high-energy photons in a strong laser field are rapidly converted into electron-position pairs. Further examples of exotic physics include breakdown of the vacuum, and novel quantum electrodynamics effects. Read more about the fundamental physics being studied in the high-field regime here.
Matter at planetary pressures
By irradiating a solid target with an intense burst of an high-power optical or x-ray laser, we can generate plasmas that are both very hot and very dense, and are similar to those thought to be found in the cores of giant planets and small stars. So-called warm dense matter of this kind is too hot to be described by conventional condensed matter physics, and too dense to be treated like an ideal hot plasma, and is therefore notoriously hard to model, and harder yet to understand. Research efforts are being directed towards unravelling the optical and transport properties of this fascinating form of matter. Read more about matter at planetary pressures here.
Dynamic compression of solids
Using high-power lasers, it is possible to compress matter rapidly and reproducibly to the kinds of pressures typically found in planetary interiors while keeping it cool enough that it remains in the solid state throughout. This gives us the opportunity to examine how a solid's microstructure (that is, the arrangement of its atoms) evolves under the dramatic compression conditions that might be encountered during meteoric or planetary impact events. Ultrafast diffraction techniques make it possible to observe the extreme plastic deformation and phase transitions precipitated by these dynamic loading conditions. Read more about compression of this kind here.
Machine learning for HED science
Computer simulations have become indispensable tools for unravelling complicated physical phenomena for which reliable experimental data is scarce, or whose underlying theory cannot practicably be solved analytically. Nowhere is this more true than in the realm of high energy density (HED) science, in which a host of complicated and overlapping processes is typically at play. However, the simulations required to model HED systems are often extremely costly. Machine-learning techniques, such as the use of neural networks, can help to circumvent this computational expense, and to solve other outstanding problems in plasma physics. Read more here.