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Title: Velocity correction for neutron activation diagnostics at the NIF

Journal Article · · Review of Scientific Instruments
DOI: https://doi.org/10.1063/1.5038734 · OSTI ID:1479059
ORCiD logo [1];  [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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The velocity distribution of the hotspot in an inertial confinement fusion implosion changes the energy spectra of fusion neutrons emitted from the experiment as a function of viewing angle. These velocity-induced spectral changes affect the response of neutron activation diagnostics (NADs) positioned around the experiment and must be accounted for to correctly extract information about areal density (ρR) asymmetry from the data. Three mechanisms through which average hotspot velocity affects NAD activation are addressed: change in activation cross section due to the Doppler shift of the mean neutron energy, kinematic focusing of neutron fluence, and change in the scattering cross section due to the Doppler shift. Using the hotspot velocity inferred from neutron time-of-flight measurements of D-T and D-D fusion neutrons, the hotspot velocity is shown to account for the observed NAD activation asymmetry in a calibration shot with negligible fuel ρR. Finally, a robust method to evaluate uncertainties in spherical-harmonic fits to the NAD data due to the velocity correction and detector uncertainty is discussed.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1479059
Alternate ID(s):
OSTI ID: 1476964
Report Number(s):
LLNL-JRNL--750006; {"Journal ID: ISSN 0034-6748",935047}
Journal Information:
Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 89; ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

References (11)

The National Ignition Facility neutron time-of-flight system and its initial performance (invited) journal October 2010
Capsule modeling of high foot implosion experiments on the National Ignition Facility journal March 2017
The Spatially Distributed Neutron Activation Diagnostic FNADs at the National Ignition Facility journal May 2017
ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology journal December 2006
Interpreting inertial fusion neutron spectra journal February 2016
Relativistic calculation of fusion product spectra for thermonuclear plasmas journal November 1998
Dynamic high energy density plasma environments at the National Ignition Facility for nuclear science research journal February 2018
Analysis of the neutron time-of-flight spectra from inertial confinement fusion experiments journal November 2015
Testing a new NIF neutron time-of-flight detector with a bibenzyl scintillator on OMEGA journal October 2012
Mode 1 drive asymmetry in inertial confinement fusion implosions on the National Ignition Facility journal April 2014
Using multiple neutron time of flight detectors to determine the hot spot velocity journal October 2018

Cited By (3)

A 3D dynamic model to assess the impacts of low-mode asymmetry, aneurysms and mix-induced radiative loss on capsule performance across inertial confinement fusion platforms journal December 2018
Progress of indirect drive inertial confinement fusion in the United States journal July 2019
Synthetic nuclear diagnostics for inferring plasma properties of inertial confinement fusion implosions journal December 2018

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