Spherical Strong-Shock generation for Shock-ignition inertial fuSion

LLE Review, Volume 141 48 Introduction Shock ignition (SI)1–5 is an advanced concept in inertial confinement fusion (ICF)6 that is very promising and has the potential to provide significantly higher gains than conventional hot-spot ignition.7 SI is a two-step process where the fuel compression and ignition phases are separated by applying a highly shaped laser pulse with a duration of several nanoseconds. The concept of separating the compression and ignition phases has already been suggested by Shcherbakov,8 but no detailed target design was presented. First, a cryogenic deuterium–tritium fuel shell is imploded to a high areal density with a low implosion velocity by a nanosecond laser driver; then a strong shock wave is launched at the end of the laser pulse that initiates ignition in the center of the compressed shell. A spherically converging shock wave is launched into the imploding shell by an abrupt increase in the power at the end of the laser pulse, producing an intensity spike of >5 # 1015 W/cm2. The shock gains strength while propagating through the converging shell and is timed so that it meets the rebounded shock from the target center inside the shell close to the inner surface. This shock collision creates new shock waves; one of them propagates back to the capsule center, enhancing the piston action on the hot spot, and triggers ignition. Because SI implosions occur at a much lower velocity than in hot-spot ignition, significantly more mass can be assembled for the same laser energy, leading to higher gain if the fuel assembly can be ignited. The energy to achieve ignition is, according to simulations,1,4 lower for SI than for hotspot ignition. Two-dimensional (2-D) simulations9 have also shown that SI targets are more resilient against hydrodynamic instabilities than hot-spot–ignition targets. The current status and the physics issues of the SI concept are reviewed in two articles that recently appeared in Nuclear Fusion.5,10