PROCEEDINGS ARTICLE | September 10, 2014
Proc. SPIE. 9211, Target Diagnostics Physics and Engineering for Inertial Confinement Fusion III
KEYWORDS: Sensors, X-rays, Scintillators, Diagnostics, Collimators, Collimation, Connectors, Oscilloscopes, Signal detection, National Ignition Facility
This paper describes the engineering architecture and function of the neutron Time-of-Flight (nToF) diagnostic suite
installed on the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). These
instruments provide key measures of neutron yield, ion temperature, drift velocity, neutron bang-time, and neutron
downscatter ratio.
Currently, there are five nToFs on three collimated lines-of-site (LOS) from 18m to 27m from Target Chamber Center,
and three positioned 4.5m from TCC, within the NIF Target Chamber but outside the vacuum and confinement boundary
by use of re-entrant wells on three other LOS.
NIF nToFs measure the time history and equivalent energy spectrum of reaction generated neutrons from a NIF
experiment. Neutrons are transduced to electrical signals, which are then carried either by coaxial or Mach-Zehnder
transmission systems that feed divider assemblies and fiducially timed digitizing oscilloscopes outside the NIF Target
Bay (TB) radiation shield wall.
One method of transduction employs a two-stage process wherein a neutron is converted to scintillation photons in
hydrogen doped plastic (20x40mm) or bibenzyl crystals (280x1050mm), which are subsequently converted to an
electrical signal via a photomultiplier tube or a photo-diode.
An alternative approach uses a single-stage conversion of neutrons-to-electrons by use of a thin (0.25 to 2 mm) Chemical
Vapor Deposition Diamond (CVDD) disc (2 to 24mm radius) under high voltage bias. In comparison to the scintillator
method, CVDDs have fast rise and decay times (<ns), have very low residual tails, are insensitive to shot gammas, and
are less sensitive to the neutron signal of interest.
