Alpha particles range modified by hot electrons adversely affects the energy threshold in direct-drive inertial confinement fusion

Implosion of a directly driven inertial confinement fusion capsule can be affected by laser-plasma instability. At relatively high laser intensities the laser energy dispersed in electron plasma wave converts a fraction of the laser energy into hot electrons that, by heating the compressed Deuterium-Tritium fuel, increases the temperature and the isentropic parameter while decreases the density. All these effects worsen the implosion process by increasing the ignition energy. Furthermore, it was found that the penetration deep of the alpha particles is also modified by changes in temperature and density, and consequently the amount of mass of the high-density fuel shell heated by alpha particles increases between 15 and 50% when accounting for hot electrons. This additional effect negatively affects the propagation of the thermonuclear burn wave and makes necessary to consider more robust laser-capsule configurations, and consequently larger laser energies, in order to achieve high energy gain.