Progress in target physics and design for heavy ion fusion

Two-dimensional, integrated calculations of a close-coupled version of the distributed radiator, heavy ion target predict gain 130 from 3.3 MJ of beam energy. To achieve these results, the case-to-capsule ratio was decreased by about 25% from the previous heavy ion targets [M. Tabak and D. Callahan-Miller, Phys. Plasmas 5, 1895 (1998)]. These targets are robust to changes in the ion stopping model because changes in the ion stopping model can be accommodated by changes to the target. The capsule is also insensitive to changes in the deuterium-tritium (DT) gas fill in the center of the capsule over the range that is of interest for target fabrication and target injection. Single-mode Rayleigh-Taylor growth rates for this capsule are smaller than those for at least one National Ignition Facility (NIF) [J. A. Paisner et al., Laser Focus World 30, 75 (1994)] design. As a result, stability issues for the heavy ion capsule can be settled on NIF. The close-coupled target also opens up the possibility of a high gain engineering test facility from a 1.5-2 MJ driver; calculations predict that gain 90 is achievable from 1.75 MJ of beam energy. Finally, the choice of hohlraum wall material, which must satisfy constraints from target physics, environment and safety, chamber design, and target fabrication, is discussed. (C) 2000 American Institute of Physics. [S1070-664X(00)90805-X].