Ion charge number and flux saturation effects in the corona of a laser-irradiated pellet

Abstract

The quasisteady structure of the corona of a laser-irradiated pellet is completely determined for arbitrary Zi (ion charge number) and rc/ra (ratio of critical and ablation radii), and for heat-flux saturation factor f above approximately 0.04 . The ion-to-electron temperature ratio at rc grows sensibly with Zi; all other quantities depend weakly and nonmonotonically on Zi. For rc/ra close to unity, and all Zi of interest (Zi<47), the flow is subsonic at rc. For a given laser power W, flux saturation may decrease (low f) or increase (high f) the ablation pressure Pa relative to the value obtained when saturation is not considered; in some cases a decrease in f with W fixed increases Pa. For intermediate f (∼0.1), Pa∝(W/r2a)2/3 ρ1/3c(ρc= critical density), independently of rc/ra; for f∼0.6, Pa is larger by a factor of about (rc/ra)2/3. For rc/ra>1.2 roughly, the mass ablation rate is C(Zi)[(mi/kZi)7 u/2 K̄r11aP5a]1/6, independent of ρc and f, and barely dependent on Zi(mi is ion mass; k, Boltzmann’s constant; K̄, conductivity coefficient; and C, a tabulated function).