Divergence of laser-generated hot electrons generated in a cone geometry

Short-pulse, ultra-intense lasers generate hot electrons at the cone tip in a Fast Ignition target. Core heating and cone-wire experiments find that about 20% of the incident laser energy is coupled into a target, but do not characterize electron propagation direction, a critical parameter for ignition. Previous studies using flat foils suggest they propagate forward, diverging by similar to 40 degrees. Buried cone targets-conical cavities in multilayer metal foils-were developed to allow divergence measurements in an FI relevant geometry. Preliminary results show increased electron divergence in a 30 mu m diameter cone tip which disappears for 90 mu m diameter tips. Implications of the experiment are discussed.