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Title: Laser entrance window transmission and reflection measurements for preheating in magnetized liner inertial fusion

Laser-driven magnetized liner inertial fusion (MagLIF) is being developed on the OMEGA Laser System to study scaling. MagLIF targets require a preheat laser entrance window that can hold the gas in the target yet allow sufficient laser energy to enter the gas. For OMEGA MagLIF targets, 1.8-μm-thick polyimide foils were found to be sufficient to hold a fuel pressure of up to 14 atm. Transmission and reflection of an OMEGA beam incident on such foils were measured with a calorimeter and time-resolved spectrometers for 2.5-ns square-shaped pulses, with energies from 60 to 200 J, focused to intensities from 0.65 to 2.2 × 10 14 W/cm 2. The laser energy transmitted in every case exceeded that required to achieve the goal of preheating the gas to 100 eV. The time-resolved measurements showed an initial period with very low, decreasing transmission, the duration of which decreased with increasing intensity, followed by a rapid transition to full transmission, accompanied by brief sidescattering of the transmitted light with a significant red shift. Reflection was always negligible. Two-dimensional radiation–hydrodynamic simulations, using 3-D ray tracing with inverse bremsstrahlung energy deposition, did not capture the rapid transition to full transmission, showing instead a slow increase in transmission,more » without significant sidescatter or red shift. Finally, we propose that full transmission is achieved by relativistic self-focusing, enhanced by focusing related to the electron density profile that forms, followed by a ponderomotive blowout of the plasma.« less
Authors:
 [1] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [3]
  1. Univ. of Rochester, NY (United States). Lab. for Laser Energetics
  2. National Cheng Kung Univ., Tainan City (Taiwan). Inst. of Space and Plasma Sciences
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Report Number(s):
SAND-2018-9666J
Journal ID: ISSN 1070-664X; 2018-25, 2378, 1420
Grant/Contract Number:
NA0001944; AR0000568; AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Rochester, NY (United States). Lab. for Laser Energetics; Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1460288
Alternate Identifier(s):
OSTI ID: 1440279; OSTI ID: 1481782

Davies, J. R., Bahr, R. E., Barnak, D. H., Betti, R., Bonino, M. J., Campbell, E. M., Hansen, E. C., Harding, D. R., Peebles, J. L., Sefkow, A. B., Seka, W., Chang, P. -Y., Geissel, M., and Harvey-Thompson, A. J.. Laser entrance window transmission and reflection measurements for preheating in magnetized liner inertial fusion. United States: N. p., Web. doi:10.1063/1.5030107.
Davies, J. R., Bahr, R. E., Barnak, D. H., Betti, R., Bonino, M. J., Campbell, E. M., Hansen, E. C., Harding, D. R., Peebles, J. L., Sefkow, A. B., Seka, W., Chang, P. -Y., Geissel, M., & Harvey-Thompson, A. J.. Laser entrance window transmission and reflection measurements for preheating in magnetized liner inertial fusion. United States. doi:10.1063/1.5030107.
Davies, J. R., Bahr, R. E., Barnak, D. H., Betti, R., Bonino, M. J., Campbell, E. M., Hansen, E. C., Harding, D. R., Peebles, J. L., Sefkow, A. B., Seka, W., Chang, P. -Y., Geissel, M., and Harvey-Thompson, A. J.. 2018. "Laser entrance window transmission and reflection measurements for preheating in magnetized liner inertial fusion". United States. doi:10.1063/1.5030107.
@article{osti_1460288,
title = {Laser entrance window transmission and reflection measurements for preheating in magnetized liner inertial fusion},
author = {Davies, J. R. and Bahr, R. E. and Barnak, D. H. and Betti, R. and Bonino, M. J. and Campbell, E. M. and Hansen, E. C. and Harding, D. R. and Peebles, J. L. and Sefkow, A. B. and Seka, W. and Chang, P. -Y. and Geissel, M. and Harvey-Thompson, A. J.},
abstractNote = {Laser-driven magnetized liner inertial fusion (MagLIF) is being developed on the OMEGA Laser System to study scaling. MagLIF targets require a preheat laser entrance window that can hold the gas in the target yet allow sufficient laser energy to enter the gas. For OMEGA MagLIF targets, 1.8-μm-thick polyimide foils were found to be sufficient to hold a fuel pressure of up to 14 atm. Transmission and reflection of an OMEGA beam incident on such foils were measured with a calorimeter and time-resolved spectrometers for 2.5-ns square-shaped pulses, with energies from 60 to 200 J, focused to intensities from 0.65 to 2.2 × 1014 W/cm2. The laser energy transmitted in every case exceeded that required to achieve the goal of preheating the gas to 100 eV. The time-resolved measurements showed an initial period with very low, decreasing transmission, the duration of which decreased with increasing intensity, followed by a rapid transition to full transmission, accompanied by brief sidescattering of the transmitted light with a significant red shift. Reflection was always negligible. Two-dimensional radiation–hydrodynamic simulations, using 3-D ray tracing with inverse bremsstrahlung energy deposition, did not capture the rapid transition to full transmission, showing instead a slow increase in transmission, without significant sidescatter or red shift. Finally, we propose that full transmission is achieved by relativistic self-focusing, enhanced by focusing related to the electron density profile that forms, followed by a ponderomotive blowout of the plasma.},
doi = {10.1063/1.5030107},
journal = {Physics of Plasmas},
number = 6,
volume = 25,
place = {United States},
year = {2018},
month = {6}
}