Lynne Alese Goodwin

Double shell capsules are an attractive alternative in inertial confinement fusion experiments due to their potential for achieving a low-convergence, robust burn 1 . However, symmetry degradation and accompanying reduced fuel confinement plagues these systems due to the joint between the two hemispheres of the outer shell. The gap widens during irradiation and this perturbation grows and imprints onto the inner shell during the collision. xRAGE Eulerian radiation-hydrodynamic simulations predict significant reductions in deuterium-tritium fusion yields compared to joint-less simulations when the depth of the outer joint is increased. We demonstrate that the technique of plating the insides of the outer gap with gold can mitigate the impact of this feature. Gold-plating in quantities comparable to or exceeding the "missing" outer shell mass shows promise toward restoring both implosion symmetry and yield closer to the joint-less levels 2 . The shape and symmetry retention in the outer and inner shells is captured in high-energy x-ray synthetic radiographs.

The LANL neutron imaging and fabrication teams completed the fabrication and inspection of the neutron imaging aperture for the National Ignition Facility (NIF) prior to first use in December 2018. The 16 layer aperture contains an array of 87 openings, manufactured by scribing 100 profiles along 20-cm lengths of thin gold foils. The openings consist of 15 penumbral and 72 triangular apertures. The 16 layers are then assembled into a single 15-mm x 16.6-mm x 200-mm component. Images produced from the array of apertures must be deconvolved in order to remove distortions caused by the extended length of the aperture. In order to deconvolve the image, the as-built aperture profile must first be characterized by measuring the scribed apertures at multiple places along their length. Equipment used for inspections included a white-light interferometer, a confocal laser scanner, and an optical coordinate measuring machine. Both sides of each layer were individually inspected, using complementary and overlapping capabilities in order to overcome the aspect ratio and feature size challenges. The result was a three dimensional, as-built model with the interior layer inspection detail overlaid to create a complete as-built model of the aperture array. This paper provides an overview of the purpose of the aperture array and a detailed discussion of the aperture inspection strategies, technology processes and challenges.

A new neutron imager, known as Neutron Imaging System North Pole, has been fielded to image the neutrons produced in the burn region of imploding fusion capsules at the National Ignition Facility. The resolution and alignment requirements and parameters that drive the design of this system are similar to the pre-existing equatorial system, there are significant changes. This work describes the parameters and limitations driving the design of this system, discusses the metrology and alignment, and shows some data from the instrument.