Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Laser-driven compact particle accelerators can provide ultrashort pulses of broadband X-rays, well suited for undertaking X-ray absorption spectroscopy measurements on a femtosecond timescale. Here the Extended X-ray Absorption Fine Structure (EXAFS) features of the K-edge of a copper sample have been observed over a 250 eV window in a single shot using a laser wakefield accelerator, providing information on both the electronic and ionic structure simultaneously. This capability will allow the investigation of ultrafast processes, and in particular, probing high-energy-density matter and physics far-from-equilibrium where the sample refresh rate is slow and shot number is limited. For example, states that replicate the tremendous pressures and temperatures of planetary bodies or the conditions inside nuclear fusion reactions. Using high-power lasers to pump these samples also has the advantage of being inherently synchronised to the laser-driven X-ray probe. A perspective on the additional strengths of a laboratory-based ultrafast X-ray absorption source is presented.

Abstract:

In this invited paper, I will touch on some highlights from my research career in the Clarendon Laboratory and in the Central Laser Facility, Rutherford Appleton Laboratory, obtained working in partnership with many outstanding international collaborators. These fall under the three broad themes. The first is novel laser-plasma interactions. The second theme is that of extreme field physics using multi-petawatt laser facilities. The third theme is that of inertial fusion studies. All of these studies indicate that an international, dual-use, 20-MJ Inertial Confinement Fusion (ICF)/Inertial Fusion Energy (IFE) facility, with the first 2-MJ at high repetition rate supplying single-shot high energy amplifiers, will open many new exciting avenues for both fundamental physics and high energy density science in the decades ahead.

Abstract:

Radio bubbles, ubiquitous features of the intracluster medium around active galactic nuclei, are known to rise buoyantly for multiple scale heights through the intracluster medium (ICM). It is an open question how the bubbles can retain their high-energy cosmic-ray content over such distances. We propose that the enhanced scattering of cosmic rays due to micromirrors generated in the ICM is a viable mechanism for confining the cosmic rays within bubbles and can qualitatively reproduce their morphology. We discuss the observational implications of such a model of cosmic-ray confinement.