title: Design of the polar neutron-imaging aperture for use at the National Ignition Facility.
abstract: The installation of a neutron imaging diagnostic with a polar view at the National Ignition Facility (NIF) required design of a new aperture, an extended pinhole array (PHA). This PHA is different from the pinhole array for the existing equatorial system due to significant changes in the alignment and recording systems. The complex set of component requirements, as well as significant space constraints in its intended location, makes the design of this aperture challenging. In addition, lessons learned from development of prior apertures mandate careful aperture metrology prior to first use. This paper discusses the PHA requirements, constraints, and the final design. The PHA design is complex due to size constraints, machining precision, assembly tolerances, and design requirements. When fully assembled, the aperture is a 15 mm × 15 mm × 200 mm tungsten and gold assembly. The PHA body is made from 2 layers of tungsten and 11 layers of gold. The gold layers include 4 layers containing penumbral openings, 4 layers containing pinholes and 3 spacer layers. In total, there are 64 individual, triangular pinholes with a field of view (FOV) of 200 μm and 6 penumbral apertures. Each pinhole is pointed to a slightly different location in the target plane, making the effective FOV of this PHA a 700 μm square in the target plane. The large FOV of the PHA reduces the alignment requirements both for the PHA and the target, allowing for alignment with a laser tracking system at NIF.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: V E
authors.initials: VE
authors.lastname: Fatherley
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551-0808, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Barker
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551-0808, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Fittinghoff
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551-0808, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Hibbard
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: J I
authors.initials: JI
authors.lastname: Martinez
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: F E
authors.initials: FE
authors.lastname: Merrill
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Oertel
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: D W
authors.initials: DW
authors.lastname: Schmidt
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Volegov
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Wilde