The affect of erbium hydride on the conversion efficience to accelerated protons from ultra-shsort pulse laser irradiated foils

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This thesis work explores, experimentally, the potential gains in the conversion efficiency from ultra-intense laser light to proton beams using erbium hydride coatings. For years, it has been known that contaminants at the rear surface of an ultra-intense laser irradiated thin foil will be accelerated to multi-MeV. Inertial Confinement Fusion fast ignition using proton beams as the igniter source requires of about 10{sup 16} protons with an average energy of about 3MeV. This is far more than the 10{sup 12} protons available in the contaminant layer. Target designs must include some form of a hydrogen rich coating that can be made thick enough to support the beam requirements of fast ignition. Work with computer simulations of thin foils suggest the atomic mass of the non-hydrogen atoms in the surface layer has a strong affect on the conversion efficiency to protons. For example, the 167amu erbium atoms will take less energy away from the proton beam than a coating using carbon with a mass of 12amu. A pure hydrogen coating would be ideal, but technologically is not feasible at this time. In the experiments performed for my thesis, ErH{sub 3} coatings on 5 {micro}m gold foils are compared with typical contaminantsmore » which are approximately equivalent to CH{sub 1.7}. It will be shown that there was a factor of 1.25 {+-} 0.19 improvement in the conversion efficiency for protons above 3MeV using erbium hydride using the Callisto laser. Callisto is a 10J per pulse, 800nm wavelength laser with a pulse duration of 200fs and can be focused to a peak intensity of about 5 x 10{sup 19}W/cm{sup 2}. The total number of protons from either target type was on the order of 10{sup 10}. Furthermore, the same experiment was performed on the Titan laser, which has a 500fs pulse duration, 150J of energy and can be focused to about 3 x 10{sup 20} W/cm{sup 2}. In this experiment 10{sup 12} protons were seen from both erbium hydride and contaminants on 14 {micro} m gold foils. Significant improvements were also observed but possibly because of the depletion of hydrogen in the contaminant layer case.« less