First implosion experiments with cryogenic thermonuclear fuel on the national ignition facility

Abstract

Non-burning thermonuclear fuel implosion experiments have been fielded on the National Ignition Facility to assess progress toward ignition by indirect drive inertial confinement fusion. These experiments use cryogenic fuel ice layers, consisting of mixtures of tritium and deuterium with large amounts of hydrogen to control the neutron yield and to allow fielding of an extensive suite of optical, x-ray and nuclear diagnostics. The thermonuclear fuel layer is contained in a spherical plastic capsule that is fielded in the center of a cylindrical gold hohlraum. Heating the hohlraum with 1.3MJ of energy delivered by 192 laser beams produces a soft x-ray drive spectrum with a radiation temperature of 300eV. The radiation field produces an ablation pressure of 100Mbar which compresses the capsule to a spherical dense fuel shell that contains a hot plasma core 80νm in diameter. The implosion core is observed with x-ray imaging diagnostics that provide size, shape, the absolute x-ray emission along with bangtime and hot plasma lifetime. Nuclear measurements provide the 14.1MeV neutron yield from fusion of deuterium and tritium nuclei along with down-scattered neutrons at energies of 1012MeV due to energy loss by scattering in the dense fuel that surrounds the central hot-spot plasma. Neutron time-of-flight spectra allow the inference of the ion temperature while gamma-ray measurements provide the duration of nuclear activity. The fusion yield from deuteriumtritium reactions scales with ion temperature, which is in agreement with modeling over more than one order of magnitude to a neutron yield in excess of 10 14 neutrons, indicating large confinement parameters on these first experiments. © 2012 IOP Publishing Ltd.