Moderate-convergence inertial confinement fusion implosions in tetrahedralhohlraums at Omega

A highly uniform thermal x-radiation field for indirect-drive inertial conf inement fusion implosions may be obtained by irradiating a four-hole, tetra hedral geometry, spherical hohlraum with all 60 Omega laser beams. Implosio n studies and calculations [J. M. Wallace , Phys. Rev. Lett. 82, 3807 (1999 )] indicate a drive uniformity comparable to that expected for the National Ignition Facility [J. A. Painser , Laser Focus World 30, 75 (1994)]. With 60 beams distributed over the cavity wall, tetrahedral hohlraums have a nat ural insensitivity to power balance and pointing errors. Standard, smooth N ova capsules imploded with this drive indicate that moderate convergence-ra tio implosions, Cr similar to 18, have measured-neutron yield to calculated -clean-one-dimensional-neutronyield ratios similar to those previously inve stigated using the comparatively poor drive uniformity of Nova cylindrical hohlraums. This may indicate that a nonsymmetry-related neutron yield degra dation mechanism, e.g., hydrodynamic mixing of cold, dense ablator material with the hot-spot region or some combination of nonsymmetry effects, is do minating in this Cr regime. (C) 2000 American Institute of Physics. [S1070- 664X(00)04305-6].