Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Recent published work has shown that the phase change of shock-compressed iron along the [001] direction does transform to the [hexagonal close-packed (hcp)] phase similar to the case for static measurements. This article provides an in-depth analysis of the experiment and nonequilibrium molecular dynamics simulations, using x-ray diffraction in both cases to study the crystal structure upon transition. Both simulation and experiment are consistent with a compression and shuffle mechanism responsible for the phase change from body-centered cubic to hcp. Also both show a polycrystalline structure upon the phase transition, due to the four degenerate directions in which the phase change can occur. © 2006 The American Physical Society.

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 (similar to 0.1 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.