SCALING LAWS FOR THERMAL-RADIATION GENERATION FROM HEAVY-ION BEAM HEATED CYLINDERS

The generation of thermal radiation by heavy ion beam heated cylinders, with parameters of relevance to indirectly driven inertial confinement fusion (ICF), is studied by means of 2-D radiation hydrodynamics simulations and by a simple model, heuristically including the 2-D effects. Scaling laws are derived for the conversion efficiency as a function of the beam and converter parameters and are found to be in agreement with the simulations for both a low-Z material (carbon) and a high-Z material (gold). The choice of the converter material is discussed. It is confirmed that for a given converter mass density and for a given (not too large) converter radius, high-Z materials achieve good conversion efficiency at the lowest deposited power (of the order of 10(16) W/g). On the other hand, for given beam parameters (ion species, ion energy, beam power and focal spot size) and converter geometry (with parameters typical of foreseen ICF targets), moderate-Z or even low-Z materials are better converters than high-Z materials.