Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The past few years have seen a rapid growth in the development and exploitation of X-ray diffraction on ultra-fast 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:

A possible new mechanism for anomalous ion heating in ultra-intense laser plasmas is considered here. This mechanism is based on the excitation of an electron two-stream instability that is driven by the fast electron beam and resonantly decays into ion-acoustic waves. These low frequency waves are then strongly damped by the ion collisions in the dense plasma. The model gives a simple explanation for the preferential heating of the bulk ion population observed in recent laser experiments in the petawatt (PW) regime. © 2005 IOP Publishing Ltd.