Two dimensional particle-in-cell simulations show that laser channeling in millimeter-scale underdense plasmas is a highly nonlinear and dynamic process involving longitudinal plasma buildup, laser hosing, channel bifurcation and self-correction, and electron heating to relativistic temperatures. The channeling speed is much less than the linear group velocity of the laser. The simulations find that low-intensity channeling pulses are preferred to minimize the required laser energy but with an estimated lower bound on the intensity of I approximately 5x10(18) W/cm(2) if the channel is to be established within 100 ps. The channel is also shown to significantly increase the transmission of an ignition pulse.
High-intensity, short-pulse laser-interaction experiments with small-mass, wedge-shaped-cavity Cu targets are presented. The diagnostics provided spatially and spectrally resolved measurements of the Cu Kα line emission at 8 keV. The conversion efficiency of short-pulse laser energy into fast electrons was inferred from the x-ray yield for wedge opening angles between 30° and 60° and for s- and p-polarized laser irradiation. Up to 36±7% conversion efficiency was measured for the narrowest wedge with p-polarization. The results are compared with predictions from two-dimensional particle-in-cell simulations.
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