Multi-axis neutron imaging at the National Ignition Facility

Abstract

Inertial confinement fusion experiments at the National Ignition Facility (NIF) rely on a neutron imager to measure the 2D size and shape of the neutron-producing region in the burning deuterium-tritium plasma. Since the existing neutron imager is located on the equator of the NIF chamber, it provides only one view of the plasma, which complicates understanding the inherently three-dimensional nature of the implosion. Attempts to use x-ray images combined with the neutron image to improve our understanding of the 3D neutron-burn volume have proved to be inconsistent with the fuel mass. This result is understandable since neutrons and x-rays are not produced or propagated in the same manner. Thus, it is desirable to use multiple neutron imagers, and we are designing two neutron imagers on lines of sight that are nearly orthogonal to the current imager, one near the pole of the chamber and one near the equator, for fielding on the NIF in the next five years. In this paper, we will discuss the current designs, including the resolution, field of view and placement in the facility that will be required to use the three orthogonal neutron imagers to measure the neutron burn volume of plasmas at NIF. Prepared by LLNL under Contract DE-AC52-07NA27344.