Capsule optimization techniques for Fast Ignition*

The general Fast Ignition scheme is well-known. Here we discuss two optimization techniques. In addition we will discuss strategies to ``sneak up'' on ignition with available drivers.The commonly discussed ignition method for Fast Ignition where heat is directly injected into the hotspot requires $\sim $5 times the hotspot energy as that associated with conventional implosions. This occurs because the fuel explodes during the run-up to ignition, wasting ignition energy on bulk fluid motion while the fuel density drops. We explore ``exploding pusher'' ignition schemes where a second implosion is driven by the injected energy. Early studies have shown that such a reimplosion can reduce the required ignition energy below the Atzeni scaling. Typical short pulse lasers deliver 20-30{\%} of their energy in a spot a few times the diffraction limit with the rest delivered in a spot 5-10 times that diameter. Survival of the final optic in energy applications will lead to large standoff requirements, large f/{\#}'s and hence spots. We describe the design of non-imaging collectors that can concentrate the incident laser light under a variety of scattering assumptions for a variety of incident illumination choices. *This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.