Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Short pulse (< 100 fs) tunable X-ray and VUV laser sources, based on the free electron laser (FEL) concept, will be a watershed for high energy density research in several areas. These new 4 ^th generation light sources will have extremely high fields and short wavelength (∼.1 nm) with peak spectral brightness -photons/(s/mrad ²/mm ²/0.1% bandwidth- 10 ¹⁰ greater than 3 ^rd generation light sources. We briefly discuss several applications: the creation of warm dense matter (WDM), probing of near solid density plasmas, and laser-plasma spectroscopy of ions in plasmas. The study of dense plasmas has been severely hampered by the fact that laser-based probes that can directly access the matter in this regime have been unavailable and these new 4 ^th generation sources will remove these restrictions. Finally, we present the plans for a user-oriented set of facilities that will incorporate high-energy, intense short-pulse, and x-ray lasers at the first x-ray FEL, the LCLS to be opened at SLAC in 2009.

Abstract:

The past few years have seen a rapid growth in the development and exploitation of X-ray diffraction on ultrafast time-scales. One area of physics which has benefited particularly from these advances is the the field of shock-waves. Whilst it has been known for many years that crystalline matter, subjected to uniaxial shock compression, can undergo plastic deformation and, for certain materials, polymorphic phase transformations, it has hitherto not been possible to observe the rearrangement of the atoms on the pertinent timescales. We have used laser-plasma generated X-rays to study how single crystals of metals (copper and iron) react to uniaxial shock compression, and observed rapid plastic flow (in the case of copper), and directly observed the famous alpha-epsilon transition in Iron. These studies have been complemented by large-scale multi-million atom molecular dynamics simulations, yielding significant information on the underlying physics.

Abstract:

Electron beam hollowing in a plasma is investigated using an analytical, rigid beam model and two different hybrid codes in an attempt to explain observations of hollow plasma formations on the back of plastic targets in experiments carried out on the Vulcan terawatt laser. The relevance of the results to electron transport in fast ignition inertial confinement fusion is considered using dimensionless scaling parameters. © 2006 IOP Publishing Ltd.