For successful laser-direct-drive inertial confinement fusion implosions, the laser irradiation must be highly uniform over the target surface. On OMEGA, multiple laser beams are used to illuminate targets quasi-uniformly. High-mode-number nonuniformities due to laser speckle on each individual beam are reduced by splitting each beam into two orthogonal polarizations (i.e., polarization smoothing, or PS) and a range of wavelengths (i.e., smoothing by spectral dispersion) that are dispersed at the target plane. However, cross-beam energy transfer (CBET) is sensitive to both the polarizations and wavelengths of the interacting beams, so the interplay between CBET and the laser-smoothing schemes results in unique intensity variation across each beam profile, which is a systematic source of low-mode drive nonuniformity on OMEGA. Here, we model these effects and find that the predicted ℓ = 1 mode in the laser-absorption distribution is consistent with the systematic core-flow direction that has been determined from the OMEGA implosion database. We also observe good agreement with the measured core-flow directions for two specific sets of implosions (one with PS, the other without PS) when we also account for the measured beam mispointing and the beam power imbalance.
Edgell, Dana, et al. "Low-mode nonuniformity in direct-drive ICF implosions due to laser smoothing techniques employed on OMEGA." Physics of Plasmas, vol. 32, no. 10, Oct. 2025. https://doi.org/10.1063/5.0273559
Edgell, Dana, Lees, Aarne, Shah, Rahul, Shvydky, Alexander, & Turnbull, David (2025). Low-mode nonuniformity in direct-drive ICF implosions due to laser smoothing techniques employed on OMEGA. Physics of Plasmas, 32(10). https://doi.org/10.1063/5.0273559
Edgell, Dana, Lees, Aarne, Shah, Rahul, et al., "Low-mode nonuniformity in direct-drive ICF implosions due to laser smoothing techniques employed on OMEGA," Physics of Plasmas 32, no. 10 (2025), https://doi.org/10.1063/5.0273559
@article{osti_2997967,
author = {Edgell, Dana and Lees, Aarne and Shah, Rahul and Shvydky, Alexander and Turnbull, David},
title = {Low-mode nonuniformity in direct-drive ICF implosions due to laser smoothing techniques employed on OMEGA},
annote = {For successful laser-direct-drive inertial confinement fusion implosions, the laser irradiation must be highly uniform over the target surface. On OMEGA, multiple laser beams are used to illuminate targets quasi-uniformly. High-mode-number nonuniformities due to laser speckle on each individual beam are reduced by splitting each beam into two orthogonal polarizations (i.e., polarization smoothing, or PS) and a range of wavelengths (i.e., smoothing by spectral dispersion) that are dispersed at the target plane. However, cross-beam energy transfer (CBET) is sensitive to both the polarizations and wavelengths of the interacting beams, so the interplay between CBET and the laser-smoothing schemes results in unique intensity variation across each beam profile, which is a systematic source of low-mode drive nonuniformity on OMEGA. Here, we model these effects and find that the predicted ℓ = 1 mode in the laser-absorption distribution is consistent with the systematic core-flow direction that has been determined from the OMEGA implosion database. We also observe good agreement with the measured core-flow directions for two specific sets of implosions (one with PS, the other without PS) when we also account for the measured beam mispointing and the beam power imbalance.},
doi = {10.1063/5.0273559},
url = {https://www.osti.gov/biblio/2997967},
journal = {Physics of Plasmas},
issn = {ISSN 1089-7674},
number = {10},
volume = {32},
place = {United States},
publisher = {AIP Publishing},
year = {2025},
month = {10}}
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 964https://doi.org/10.1016/j.nima.2020.163774
Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, Vol. 201, Issue 1065, p. 192-196https://doi.org/10.1098/rspa.1950.0052