Demonstration of a time-integrated short line of sight neutron imaging system for inertial confinement fusion

Abstract

The Neutron Imaging System (NIS) is an important diagnostic for understanding implosions of deuterium-tritium capsules at the National Ignition Facility. While the detectors for the existing system must be positioned 28 m from the source to produce sufficient imaging magnification and resolution, recent testing of a new short line of sight neutron imaging system has shown sufficient resolution to allow reconstruction of the source image with quality similar to that of the existing NIS on a 11.6 m line of sight. The new system used the existing pinhole aperture array and a stack of detectors composed of 2 mm thick high-density polyethylene converter material followed by an image plate. In these detectors, neutrons enter the converter material and interact with protons, which recoil and deposit energy within the thin active layer of the image plate through ionization losses. The described system produces time-integrated images for all neutron energies passing through the pinhole. We present details of the measurement scheme for this novel technique to produce energy-integrated neutron images as well as source reconstruction results from recent experiments at NIF.

Dynamic high energy density plasma environments at the National Ignition Facility for nuclear science research

“…This imager uses a detector stack of four pair of 2 mm polyethylene sheets followed by image plates. The detector relies on (n, p) reactions in the high-density polyethylene to produce protons that interact with the image plate to record an image [93]. While it has lower efficiency than the 50 mm thick BCF-99-55 scintillating fiber Figure 16.…”

“…This imager uses a detector stack of four pair of 2 mm polyethylene sheets followed by image plates. The detector relies on (n, p) reactions in the high-density polyethylene to produce protons that interact with the image plate to record an image [93]. While it has lower efficiency than the 50 mm thick BCF-99-55 scintillating fiber array used on 90-315, this imaging stack has excellent resolution (∼650 μm FWHM point spread function versus 1.1 mm for the BCF-99-55 fiber array) and allows imaging on an 8.2 m LOS.…”

The neutron imaging system for inertial confinement fusion at the 100 kilo-Joule laser facility

“…Neutron Imaging System (NIS) has been used to infer the hot spot conditions in inertial confinement fusion (ICF) implosions [1][2][3]. Typically, the shape and size of hot-spot can be inferred from the primary neutron image [3][4][5][6], and the down-scattered neutron image provides the information of the cold fuel [7][8][9]. Moreover, the 3D neutron emissivity can be reconstructed with multi-line-of-sight neutron image measurement [10].…”

Design of Neutron Imaging Aperture for Inertial Confinement Fusion in Laser Fusion Research Center

“…The neutron emission image of compressed capsules filled with fuels in inertial confinement fusion (ICF) implosions can be measured by the neutron imaging system (NIS) [1][2][3]. The asymmetry and size of hot-spot can be inferred from the primary neutron image [3][4][5][6], while the down-scattered neutron image provides the information of the cold fuel [7][8][9]. Both the images of hot-spot and cold fuel are required to distinguish failure mechanisms and tune the implosions.…”