Implosion theory and hot spot features for an indirectly driven optimized capsule

Abstract

The implosion of an indirectly driven optimized capsule for ICF is analyzed. We distinguish two media in the non-ablated capsule: the central hot spot and the cold shell, the boundary of the hot spot is defined such that this medium has no heat conduction losses, the features of each medium are described by mean quantities. The integral momentum conservation equation for volume of variable mass gives the rocket model for the acceleration phase, it is corrected to take into account the beginning of the acceleration. With approximations it gives the maximum implosion velocity. The entropy conservation is generalized for a non uniform medium of variable mass, it indicates what is the invariant quantity hidden in the hot spot during implosion and shows that the deceleration is approximately isobaric. The hot spot features and the implosion velocity in deceleration can be deduced from these results. The hot spot mass is obtained by integrating the heat conduction flux inside the hot spot. In the capsule parameters determining the ignition condition, the mass and the entropy of gas has to be included. All these results are compared with numerical simulations.