Three-dimensional characterization of the third line-of-site neutron imaging pinhole at NIF

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.