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Title: Velocity correction for neutron activation diagnostics at the NIF

Abstract

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.

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1479059
Alternate Identifier(s):
OSTI ID: 1476964
Report Number(s):
LLNL-JRNL-750006
Journal ID: ISSN 0034-6748; 935047
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 89; Journal Issue: 10; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; Lasers

Citation Formats

Rinderknecht, Hans G., Bionta, R., Grim, G., Hatarik, R., Khater, H., Schlossberg, D., and Yeamans, C. Velocity correction for neutron activation diagnostics at the NIF. United States: N. p., 2018. Web. doi:10.1063/1.5038734.
Rinderknecht, Hans G., Bionta, R., Grim, G., Hatarik, R., Khater, H., Schlossberg, D., & Yeamans, C. Velocity correction for neutron activation diagnostics at the NIF. United States. doi:10.1063/1.5038734.
Rinderknecht, Hans G., Bionta, R., Grim, G., Hatarik, R., Khater, H., Schlossberg, D., and Yeamans, C. Mon . "Velocity correction for neutron activation diagnostics at the NIF". United States. doi:10.1063/1.5038734. https://www.osti.gov/servlets/purl/1479059.
@article{osti_1479059,
title = {Velocity correction for neutron activation diagnostics at the NIF},
author = {Rinderknecht, Hans G. and Bionta, R. and Grim, G. and Hatarik, R. and Khater, H. and Schlossberg, D. and Yeamans, C.},
abstractNote = {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.},
doi = {10.1063/1.5038734},
journal = {Review of Scientific Instruments},
number = 10,
volume = 89,
place = {United States},
year = {2018},
month = {10}
}

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