Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The propagation of electrostatic plasma waves having relativistic phase speed and amplitude has been studied. The plasma is described as a warm, relativistic, collisionless, nonequilibrium, one-dimensional electron fluid. Wave-breaking limits for the electrostatic field are calculated for nonrelativistic initial plasma temperatures and arbitrary phase velocities, and a correspondence between wave breaking and background particle trapping has been uncovered. Particular care is given to the ultrarelativistic regime (γ2 kB T0 (me c2) 1), since conflicting results for this regime have been published in the literature. It is shown here that the ultrarelativistic wave-breaking limit will reach arbitrarily large values for γ →∞ and fixed initial temperature. Previous results claiming that this limit is bounded even in the limit γ →∞ are shown to suffer from incorrect application of the relativistic fluid equations and higher, more realistic wave-breaking limits are appropriate. © 2006 American Institute of Physics.

Abstract:

We describe measurements characterizing the interaction of ultra-high intensity Petawatt laser pulses with solid targets. Experiments were performed on the Petawatt laser at RAL, and the Titan laser at LLNL. © 2006 Optical Society of America.

Abstract:

In situ diffraction is a technique to probe directly the lattice response of materials during the shock loading process. It is used to record diffraction patterns from multiple lattice planes simultaneously. The application of this technique is described for laser-based shock experiments. The approach to analyze in situ wide-angle diffraction data is discussed. This is presented in the context of single crystal [001] iron shock experiments where uniaxial compression of the bee lattice by up to 6% was observed. Above the alpha-epsilon transition pressure, the lattice showed a collapse along the [001] direction by 15-18%. Additional diffraction lines appear that confirm the transformation of the iron crystal from the initial bee phase to the hcp phase. (C) 2006 Elsevier Ltd. All rights reserved.

Abstract:

We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the nonlinear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may be achieved. © 2006 The American Physical Society.