Pulse shaping for ignition and gain of an indirectly driven target

Abstract

A detailed study of the problem of ignition of the intended indirectly driven ‘‘point design target’’ [J. Lindl, Phys. Plasmas 2, 3933 (1995)] for the U.S. National Ignition Facility is presented. First a multistep pressure pulse which ignites the target (without its ablator) is found and the effect of changing the timing of the different shocks on the target yield is analysed in detail. A radiation drive which nearly reproduces such a pressure pulse at the ablator/fuel interface is then constructed. The resulting radiation drive is similar to the one used by the U.S. workers but has a 3 percent higher peak value. An operating window of about 35 eV width is found around the optimum maximum drive temperature. Below this window the target fails because adequate implosion velocities are not achieved, while above it the main fuel is raised to high entropies resulting in low compressions, despite high implosion velocities. These calculations represent the first independent confirmation, outside the weapons laboratories, that ignition and gain can be achieved near the operating parameters for the above target.