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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:
Grant/Contract Number:
NA0001944; AR0000568
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
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