CONFIGURATIONS OF RADIATION-DRIVEN TARGETS FOR HEAVY-ION FUSION

The baseline configuration of a radiation driven target for heavy ion fusion is a quasi-cylindrical hohlraum containing a fusion capsule and with radiation converters placed at opposite ends of the hohlraum. Ion beams enter each converter from opposite directions and are stopped by the material inside the converters. For a capsule that absorbs about 1 MJ of radiation energy and has an initial radius of 0.234 cm, calculations using the viewfactor code GERTIE indicate that the maximum initial capsule-to-hohlraum surface area ratio that can provide adequate time dependent symmetry for a capsule implosion is about 0.075. These calculations take into account the substantial inward expansion of the hohlraum wall. The capsule implosion and the wall motion are calculated using the one dimensional radiation hydrodynamics code HYADES and the conversion efficiencies of the radiation converters are studied using the two dimensional radiation hydrodynamics code LASNEX. The efficiency of energy coupling between the hohlraum and the capsule is 21%, the peak hohlraum temperature is 0.26 keV, and the energy gain can be as high as 80. If the converters are placed outside the hohlraum, their radii can be varied according to the beam focusing requirements, while the hohlraum dimensions remain unchanged. This provides a convenient way of calculating target gain as a function of converter radius. By bending the radiation converters by 90 degrees, we can obtain a hohlraum configuration in which the ion beams can enter the target from a single direction, eliminating the need for bending the beams by 180 degrees.