2.C Limits on the Flux Limiter and Preheat from Analysis of Implosion Experiments with 1054-nm Illumination

Thermal electron transport plays an important role in the performance of direct-drive inertial-confinement-fusion targets. The laser energy absorbed in the corona is carried into the dense target through thermal electron transport and is converted into kinetic energy through the ablation process. The efficiency of the target drive and of the absorption of the laser light depend to a large extent on the efficiency of the thermal transport. In laser-fusion hydrodynamic codes the thermal transport is calculated with a diffusion model using Spitzer's model for thermal cond~c t iv i t y .~ In the steep temperature gradients which exist in laser-fusion targets, the diffusion model with Spitzer's conductivity yields thermal fluxes larger than those available from the free-streaming electron^.^ Code calculations, therefore, usually impose an upper limit on the conductivity given by some fraction of the freestreaming value, with the form Q, = fnkT(kT/m)Ib where the parameter f, known as the flux limiter, is to be determined through experiments or from solutions to the Boltzmann equation.