Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Reduction of proton acceleration in the interaction of a high-intensity, piosecond laser with a 50-μm aluminum target was observed when 0.1-6 μm of plastic was deposited on the back surface (opposite side of the laser). The maximum energy and number of energetic protons observed at the back of the target were greatly reduced in comparison to pure aluminum and plastic targets of the same thickness. This is attributed to the effect of the interface between the layers. Modeling of the electron propagation in the targets using a hybrid code showed strong magnetic-field generation at the interface and rapid surface heating of the aluminum layer, which may account for the results. © 2006 American Institute of Physics.

Abstract:

The effect of focusing conditions in laser wakefield acceleration is studied. Short focal length geometries produce large dark currents while longer focal lengths produce narrow energy spread beams. © 2006 Optical Societ of America.

Abstract:

The Staged Electron Laser Acceleration - Laser Wakefield (STELLA-LW) experiment is investigating two new methods for laser wakefield acceleration (LWFA) using the TW CO2 laser available at the Brookhaven National Laboratory Accelerator Test Facility. The first is seeded self-modulated LWFA where an ultrashort electron bunch (seed) precedes the laser pulse to generate a wakefield that the laser pulse subsequently amplifies. The second is pseudo-resonant LWFA where nonlinear pulse steepening of the laser pulse occurs in the plasma allowing the laser pulse to generate significant wakefields. The status of these experiments is reviewed. Evidence of wakefield generation caused by the seed bunches has been obtained as well as preliminary energy gain measurements of a witness bunch following the seeds. Comparison with a 1-D linear model for the wakefield generation appears to agree with the data. © 2006 American Institute of Physics.

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.