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Title: Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments

Planar laser-plasma interaction (LPI) experiments at the National Ignition Facility (NIF) have allowed access for the rst time to regimes of electron density scale length (~500 to 700 μm), electron temperature (~3 to 5 keV), and laser intensity (6 to 16 x 10 14 W/cm 2) that are relevant to direct-drive inertial confinement fusion ignition. Unlike in shorter-scale-length plasmas on OMEGA, scattered-light data on the NIF show that the near-quarter-critical LPI physics is dominated by stimulated Raman scattering (SRS) rather than by two-plasmon decay (TPD). This difference in regime is explained based on absolute SRS and TPD threshold considerations. SRS sidescatter tangential to density contours and other SRS mechanisms are observed. The fraction of laser energy converted to hot electrons is ~0.7% to 2.9%, consistent with observed levels of SRS. The intensity threshold for hot-electron production is assessed, and the use of a Si ablator slightly increases this threshold from ~4 x 10 14 to ~6 x 10 14 W/cm 2. These results have significant implications for mitigation of LPI hot-electron preheat in direct-drive ignition designs.
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Univ. of Rochester, NY (United States). Lab. for Laser Energetics
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Naval Research Lab. (NRL), Washington, DC (United States)
Publication Date:
Report Number(s):
2017-65; 1374
Journal ID: ISSN 0031-9007; PRLTAO; 2017-65, 2331, 1374; TRN: US1801712
Grant/Contract Number:
NA0001944
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 5; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Laboratory for Laser Energetics, University of Rochester; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); Univ. of Rochester, NY (United States); New York State Energy Research and Development Authority (NYSERDA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1423128
Alternate Identifier(s):
OSTI ID: 1418402

Rosenberg, M. J., Solodov, A. A., Myatt, J. F., Seka, W., Michel, P., Hohenberger, M., Short, R. W., Epstein, R., Regan, S. P., Campbell, E. M., Chapman, T., Goyon, C., Ralph, J. E., Barrios, M. A., Moody, J. D., and Bates, J. W.. Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments. United States: N. p., Web. doi:10.1103/PhysRevLett.120.055001.
Rosenberg, M. J., Solodov, A. A., Myatt, J. F., Seka, W., Michel, P., Hohenberger, M., Short, R. W., Epstein, R., Regan, S. P., Campbell, E. M., Chapman, T., Goyon, C., Ralph, J. E., Barrios, M. A., Moody, J. D., & Bates, J. W.. Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments. United States. doi:10.1103/PhysRevLett.120.055001.
Rosenberg, M. J., Solodov, A. A., Myatt, J. F., Seka, W., Michel, P., Hohenberger, M., Short, R. W., Epstein, R., Regan, S. P., Campbell, E. M., Chapman, T., Goyon, C., Ralph, J. E., Barrios, M. A., Moody, J. D., and Bates, J. W.. 2018. "Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments". United States. doi:10.1103/PhysRevLett.120.055001.
@article{osti_1423128,
title = {Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments},
author = {Rosenberg, M. J. and Solodov, A. A. and Myatt, J. F. and Seka, W. and Michel, P. and Hohenberger, M. and Short, R. W. and Epstein, R. and Regan, S. P. and Campbell, E. M. and Chapman, T. and Goyon, C. and Ralph, J. E. and Barrios, M. A. and Moody, J. D. and Bates, J. W.},
abstractNote = {Planar laser-plasma interaction (LPI) experiments at the National Ignition Facility (NIF) have allowed access for the rst time to regimes of electron density scale length (~500 to 700 μm), electron temperature (~3 to 5 keV), and laser intensity (6 to 16 x 1014 W/cm2) that are relevant to direct-drive inertial confinement fusion ignition. Unlike in shorter-scale-length plasmas on OMEGA, scattered-light data on the NIF show that the near-quarter-critical LPI physics is dominated by stimulated Raman scattering (SRS) rather than by two-plasmon decay (TPD). This difference in regime is explained based on absolute SRS and TPD threshold considerations. SRS sidescatter tangential to density contours and other SRS mechanisms are observed. The fraction of laser energy converted to hot electrons is ~0.7% to 2.9%, consistent with observed levels of SRS. The intensity threshold for hot-electron production is assessed, and the use of a Si ablator slightly increases this threshold from ~4 x 1014 to ~6 x 1014 W/cm2. These results have significant implications for mitigation of LPI hot-electron preheat in direct-drive ignition designs.},
doi = {10.1103/PhysRevLett.120.055001},
journal = {Physical Review Letters},
number = 5,
volume = 120,
place = {United States},
year = {2018},
month = {1}
}

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