Title: Isolating and quantifying cross-beam energy transfer in direct-drive implosions on OMEGA and the National Ignition Facility

Abstract

The angularly-resolved mass ablation rates and ablation front trajectories for Si-coated CH targets were measured in direct-drive inertial confinement fusion experiments to quantify crossbeam energy transfer (CBET) while constraining the hydrodynamic coupling. A polar-direct-drive laser configuration was used, where the equatorial laser beams were dropped from a symmetric direct-drive configuration to suppress CBET at the pole, while allowing it to persist at the equator. The combination of low- and high-CBET conditions in the same implosion allowed the effects of CBET on the ablation rate and ablation pressure to be decoupled from the other physics effects that influence laser-coupling. Hydrodynamic simulations performed without CBET reproduced the measured ablation rate and ablation front trajectory at the pole of the target, verifying that the other laser-coupling physics effects are well-modeled when CBET effects are negligible. The simulated mass ablation rates and ablation front trajectories were in excellent agreement with the measurements at all angles when a CBET model based on Randall’s equations [C. J. Randall et al., Phys. Fluids 24, 1474 (1981)] was included into the simulations with an optimized multiplier on the CBET gain factor. These measurements were performed on both OMEGA and the National Ignition Facility to access a wide rangemore » of plasma conditions, laser intensities, and laser beam geometries. Furthermore, the presence of the CBET gain multiplier required to match the data in all of the configurations tested suggests that additional physics effects, such as intensity variations due to diffraction, shortcomings of extending the 1-D Randall model to 3-D, or polarization effects, should be explored to explain the differences in observed and predicted drive.« less

Authors:

Davis, A. K. ^[1]; Cao, D. ^[1]; Michel, D. T. ^[1]; Hohenberger, M. ^[1]; Edgell, D. H. ^[1]; Epstein, R. ^[1]; Goncharov, V. N. ^[1]; Hu, S. X. ^[1]; Igumenshchev, I. V. ^[1]; Marozas, J. A. ^[1]; Maximov, A. V. ^[1]; Myatt, J. F. ^[1]; Radha, P. B. ^[1]; Regan, S. P. ^[1]; Sangster, T. C. ^[1]; Froula, D. H. ^[1]

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+ Show Author Affiliations

1. Univ. of Rochester, Rochester, NY (United States)

Publication Date:

Wed Apr 20 00:00:00 EDT 2016

Research Org.:

Univ. of Rochester, NY (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1255524

Grant/Contract Number:  

NA0001944

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 23; Journal Issue: 5; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; laser ablation; x-ray imaging; trajectory models; energy transfer; experiment design