Electron Generation in Fast Ignition Targets

Recent experiments on thin-wall cone/wire targets, have shown 15\% conversion of laser energy to a 40~$\mu$m $\phi$ wire via fast electrons [1]. Electrostatic fields on the cone exterior restrict electron motion unlike in a real fast ignition target where such fields are suppressed by the surrounding blow-off plasma. To eliminate such constraints, we have emulated those conditions with thick-wall ($\sim$200\,$\mu{m}$) aluminum cones in experiments with 150~J, 1~ps laser pulses at the Titan laser facility. The resulting electrons were imaged using $K_{\alpha}$ fluorescence from Cu layers buried in the Al in front of the cone tip and quantified with a single hit CCD camera to get directionality and coupling efficiency. Results will be discussed at the meeting. \vskip6pt \noindent [1] J.A. King, et al., submitted to Phys. Rev. Lett. (2007).