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Title: Three-dimensional modeling of direct-drive cryogenic implosions on OMEGA

The effects of large-scale (with Legendre modes ≲10) laser-imposed nonuniformities in direct-drive cryogenic implosions on the OMEGA laser system are investigated using three-dimension hydrodynamic simulations performed using a newly developed code ASTER. Sources of these nonuniformities include an illumination pattern produced by 60 OMEGA laser beams, capsule offsets (~10 to 20 μm), and imperfect pointing, energy balance, and timing of the beams (with typical σ rms ~10 μm, 10%, and 5 ps, respectively). Two implosion designs using 26-kJ triple-picket laser pulses were studied: a nominal design, in which a 880-μm-diameter capsule is illuminated by the same-diameter beams, and a “R75” design using a capsule of 900 μm in diameter and beams of 75% of this diameter. Simulations found that nonuniformities because of capsule offsets and beam imbalance have the largest effect on implosion performance. These nonuniformities lead to significant distortions of implosion cores resulting in an incomplete stagnation. The shape of distorted cores is well represented by neutron images, but loosely in x-rays. Simulated neutron spectra from perturbed implosions show large directional variations and up to ~ 2 keV variation of the hot spot temperature inferred from these spectra. The R75 design is more hydrodynamically efficient because of mitigation ofmore » crossed-beam energy transfer, but also suffers more from the nonuniformities. Furthermore, simulations predict a performance advantage of this design over the nominal design when the target offset and beam imbalance σ rms are reduced to less than 5 μm and 5%, respectively.« less
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  1. Univ. of Rochester, Rochester, NY (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 5; Journal ID: ISSN 1070-664X
American Institute of Physics (AIP)
Research Org:
Univ. of Rochester, Rochester, NY (United States)
Sponsoring Org:
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; neutrons; hydrodynamics; x-ray imaging; cryogenic; shell model
OSTI Identifier: