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Title: Understanding the effects of laser imprint on plastic-target implosions on OMEGA

Understanding the effects of laser imprint on target performance is critical to the success of direct-drive inertial confinement fusion. Directly measuring the disruption caused by laser imprints to the imploding shell and hot-spot formation, in comparison with multidimensional radiation–hydrodynamic simulations, can provide a clear picture of how laser nonuniformities cause target performance to degrade. With the recently developed x-ray self-emission imaging technique and the state-of-the-art physics models recently implemented in the two-dimensional hydrocode DRACO, a systematic study of laser-imprint effects on warm target implosions on OMEGA has been performed using both experimental results and simulations. By varying the laser-picket intensity, the imploding shells were set at different adiabats (from α = 2 to α = 6). As the shell adiabats decreased, it was observed that (1) the measured shell thickness at the time the hot spot lit up became larger than the uniform one-dimensional (1-D) predictions; (2) the hot-spot core emitted earlier than the corresponding 1-D predictions; (3) the measured neutron yield first increased then decreased as the shell adiabat α was reduced; and (4) the hot-spot size reduced as α decreased for cases where SSD (smoothing by spectral dispersion) was on but became larger for low-α shots in casesmore » where SSD was off. Most of these experimental observations are well reproduced by DRACO simulations with laser imprints including modes up to λ max = 200. In addition, these studies identify the importance of laser imprint as the major source of degrading target performance for OMEGA implosions of adiabat α ≤ 3. Mitigating laser imprints is required to improve low-α target performance.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1]
  1. Univ. of Rochester, Rochester, NY (United States). Lab. for Laser Energetics
Publication Date:
Grant/Contract Number:
NA0001944
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 10; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Rochester, Rochester, NY (United States). Lab. for Laser Energetics
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; neutrons; x-ray imaging; thermal models; inertial confinement; cameras
OSTI Identifier:
1328780
Alternate Identifier(s):
OSTI ID: 1328444

Hu, S. X., Michel, D. T., Davis, A. K., Betti, R., Radha, P. B., Campbell, E. M., Froula, D. H., and Stoeckl, C.. Understanding the effects of laser imprint on plastic-target implosions on OMEGA. United States: N. p., Web. doi:10.1063/1.4962993.
Hu, S. X., Michel, D. T., Davis, A. K., Betti, R., Radha, P. B., Campbell, E. M., Froula, D. H., & Stoeckl, C.. Understanding the effects of laser imprint on plastic-target implosions on OMEGA. United States. doi:10.1063/1.4962993.
Hu, S. X., Michel, D. T., Davis, A. K., Betti, R., Radha, P. B., Campbell, E. M., Froula, D. H., and Stoeckl, C.. 2016. "Understanding the effects of laser imprint on plastic-target implosions on OMEGA". United States. doi:10.1063/1.4962993. https://www.osti.gov/servlets/purl/1328780.
@article{osti_1328780,
title = {Understanding the effects of laser imprint on plastic-target implosions on OMEGA},
author = {Hu, S. X. and Michel, D. T. and Davis, A. K. and Betti, R. and Radha, P. B. and Campbell, E. M. and Froula, D. H. and Stoeckl, C.},
abstractNote = {Understanding the effects of laser imprint on target performance is critical to the success of direct-drive inertial confinement fusion. Directly measuring the disruption caused by laser imprints to the imploding shell and hot-spot formation, in comparison with multidimensional radiation–hydrodynamic simulations, can provide a clear picture of how laser nonuniformities cause target performance to degrade. With the recently developed x-ray self-emission imaging technique and the state-of-the-art physics models recently implemented in the two-dimensional hydrocode DRACO, a systematic study of laser-imprint effects on warm target implosions on OMEGA has been performed using both experimental results and simulations. By varying the laser-picket intensity, the imploding shells were set at different adiabats (from α = 2 to α = 6). As the shell adiabats decreased, it was observed that (1) the measured shell thickness at the time the hot spot lit up became larger than the uniform one-dimensional (1-D) predictions; (2) the hot-spot core emitted earlier than the corresponding 1-D predictions; (3) the measured neutron yield first increased then decreased as the shell adiabat α was reduced; and (4) the hot-spot size reduced as α decreased for cases where SSD (smoothing by spectral dispersion) was on but became larger for low-α shots in cases where SSD was off. Most of these experimental observations are well reproduced by DRACO simulations with laser imprints including modes up to λmax = 200. In addition, these studies identify the importance of laser imprint as the major source of degrading target performance for OMEGA implosions of adiabat α ≤ 3. Mitigating laser imprints is required to improve low-α target performance.},
doi = {10.1063/1.4962993},
journal = {Physics of Plasmas},
number = 10,
volume = 23,
place = {United States},
year = {2016},
month = {10}
}