Improvement in the heating efficiency of fast ignition inertial confinement fusion through suppression of the preformed plasma

The study of fast electron spectrum optimization by suppression of preformed plasma in fast ignition targets is presented in this work. Integrated fast-electron spectra for electron energies below 3 MeV-the energy range responsible for core heating-are compared for different preformed plasma conditions. The pulse contrast (the ratio of peak-to-pedestal laser intensities) is compared for 10(8), 10(9) and 10(11) conditions at constant laser energy (similar to 500 J), pulse duration (2 ps), spot size (30% encircled energy on 50 mu m diameter) and laser intensity (around 1 x 10(19) W cm(-2)). The best electron spectrum optimization, consisting of maximized electron number for energies below 3 MeV was obtained with 14 mu m thick cone targets. The energy coupling efficiency from heating laser to core plasma, assuming typical core plasma parameters, was estimated to be 2%, although 0.37% was obtained with previous conditions with poor pulse contrast and a 7 mu m thick cone target.