Role of laser beam geometry in improving implosion symmetry and performance for indirect-drive inertial confinement fusion

The role of a high-Z radiation cavity or hohlraum in inertial confinement fusion is to convert laser energy into soft x-ray energy, in a highly spatially symmetric manner, so that a centrally located capsule containing deuterium and tritium can be uniformly imploded. In practice, however, the asymmetry introduced by the small number of high intensity laser beams can introduce significant perturbations in the drive uniformity. Experiments performed on Nova (10 beams) [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)] and Omega (using 40 beams) [J. M. Sources, R. L. McCrory, C. P. Verdon et al., Phys. Plasmas 3, 2108 (1996)] demonstrate a significant improvement in symmetry and target performance from a fourfold increase in the number of laser beams.