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

Abstract

Neutron Imaging System (NIS) has been used to image the burn volume and cold fuel volume of imploding fusion capsules. In this work, we present a design of neutron imaging aperture for inertial confinement fusion in Laser Fusion Research Center. Since the total neutron yield should be less than 1014, the penumbral aperture has been chosen. A geometric model has been developed to assess the performance of the neutron imaging system, including the spatial resolution, the field of view and the signal-to-noise ratio. This model reproduces the performances of neutron image systems on OMEGA. The spatial resolution of designed NIS is about 22 μm for a field of view of 250 μm. The signal-to-noise ratio can be better than 10, if the neutron yield is higher than 1013.

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

“…The penumbral imaging technology has been chosen for the neutron imaging system with the implosion neutron yield of less than 1 × 10 14 at the 100 kilo-Joule laser facility. The biconicshaped aperture [1,2,[13][14][15]18] is one of the major components of neutron imaging system. The biconic-shaped aperture has been used to measure the ICF neutron source [13] since twenty years ago at the OMEGA laser facility.…”

“…The performance characteristics of neutron imaging system is determined by the shape and size of the aperture. The biconic-shaped aperture, as shown in figure 1, can be described by three radii, including the input radius R1, the waist radius R2 and the exit radius R3, and the aperture length d. We developed a geometric model [18] for fast parameter scan based on the ray-tracing method. The neutron image is coded while passing through the aperture.…”

“…The other parameters were determined by parameter scan with the geometric model [18]. Given aperture length, R1 and R3, and scanning Lo and R2, FOV and δ bic can be calculated with the ray-tracing method based on the geometry.…”

“…The neutron point spread function can be calculated by the ray-tracing method as described in ref. [18]. The profile in the penumbra is the convolution of the neutron source and the neutron point spread function.…”

“…Considering the neutron yield limitation of less than 1 × 10 14 at the 100 kilo-Joule laser facility, once called SG III [16,17], a neutron imaging system based on the penumbral aperture has been designed for inertial confinement fusion implosions at the 100 kilo-Joule laser facility [18]. The neutron imaging system was constructed and installed at the 100 kilo-Joule laser facility in 2020, and used to measure the neutron emissivity of exploded implosions in 2021.…”