Prof Peter Norreys FInstP;

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 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.

Abstract:

The operation of target diagnostics in a high-energy petawatt laser environment is made challenging by the large number of energetic electrons, hard x rays, and energetic particles produced in laser-target interactions. The charged particles and x rays from the target create secondary radiation and a large electromagnetic pulse (EMP) when they hit structures inside the target chamber. The primary particles create secondary particles and radiation that can create excessive background in sensitive detectors. The large EMP can impair or damage electronic equipment and detectors, especially inside the target chamber. Shielding and EMP mitigation strategies developed during experiments at the Rutherford Appleton Vulcan petawatt laser facility will be presented for a variety of detection systems, such as single-photon-counting x-ray charge-coupled device cameras, multiple diamond x-ray detectors, and scintillator-photomultiplier detectors. These strategies will be applied to the development of diagnostic systems for the OMEGA EP, high-energy petawatt laser facility, currently under construction at the Laboratory for Laser Energetics. © 2006 American Institute of Physics.

Abstract:

With the increasing number of multi-terawatt (1012 W) and petawatt (1015 W) laser interaction facilities being built, the need for a detailed understanding of the potential radiological hazards is required and their impact on personnel is of major concern. Experiments at a number of facilities are being undertaken to achieve this aim. This paper describes the recent work completed on the Vulcan petawatt laser system at the CCLRC Rutherford Appleton Laboratory, where photon doses of up to 43 mSv at 1 m per shot have been measured during commissioning studies. It also overviews the shielding in place on the facility in order to comply with the Ionising Radiation Regulations 1999 (IRR99), maintaining a dose to personnel of less than 1 mSv yr-1 and as low as reasonably practicable (ALARP). © 2006 IOP Publishing Ltd.