LLE Review 159

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• Review 159 Editor

Highlights

This volume of LLE Review 159, covering the period April–June 2019, is sectioned among research areas at LLE and external users of the Omega Laser Facility. Articles appearing in this volume are the principal summarized results of long-form research articles. Readers seeking a more-detailed account of research activities are invited to seek out the primary materials appearing in print, detailed in the publications and presentations section at the end of this volume.

Highlights of research presented in this volume include the following:

• K. S. Anderson et al. present simulation data that suggest cross-beam energy transfer (CBET) as mitigating the deleterious effects of offset (p. 127). These simulations are shown to compare better against target experiments with offset when CBET is included.
• J. A. Marozas and E. M. Campbell present a design to field polar-direct-drive (PDD) experiments on the SG-III facility that include wavelength detuning for CBET mitigation (p. 130). Although some laser modifications are necessary at the facility, SG-III presents a viable alternative to the National Ignition Facility (NIF) to field PDD experiments and further progress in direct-drive inertial confinement fusion (ICF).
• S. X. Hu et al. present justification and simulation results for direct-drive double-shell implosions in order to better approach ignition (p. 134). In the NIF design presented, fusion energy yields of 0.3 to 1.0 MJ can be obtained according to high-mode DRACO simulations.
• D. Haberberger et al. detail measurements showing early material release on the backside of a CH shell at conditions relevant to ICF (p. 138). It is hypothesized that this phenomenon could be the cause for degraded performance in current ICF experiments.
• A. Lees and H. Aluie demonstrate how to include baroclinity into the energy budget through the use of scale decomposition (p. 142). Mechanisms for “baropyncal work” are also reproduced in direct numerical simulation results for compressible turbulence.
• A. S. Davies et al. present Thomson-scattering data showing electron density and temperature evolution in a laser-produced plasma over 50 ps (p. 145). The results suggest evolution was slower compared to calculations and propose limitations to transfer efficiencies in the linear regime for Raman plasma amplification.
• P. Franke et al. detail efforts to create and control ionization fronts using flying focus (p. 149). A theory was developed that reproduced the observed data.
• A. J. Howard et al. show theory and simulation results for photon frequency upshifting caused by ionization fronts created with a flying focus (p. 153). Analytic models predict this scheme could be a novel tabletop source of spatially coherent x rays.
• A. L. Milder et al. present Thomson-scattering data showing the picosecond evolution of a non-Maxwellian electron distribution for a 2.4 × 10¹⁴ W/cm² laser-produced plasma (p. 156). Calculations from the Vlasov–Fokker–Planck code K2 showed that ionization physics was necessary to reproduce the observed data.
• R. Paul, S. X. Hu, and V. V. Karasiev present a first-principles construction of a high pressure–temperature (up to 4 TPa and 26,000 K) phase diagram of Si that revealed new stable phases (p. 159). The methodology centered on Mermin’s extension of Kohn–Sham density functional theory and ab initio lattice dynamics of perfect crystals.
• W. Theobald et al. present a comparison between UV equivalent-target-plane (UVETP) measurements and x-ray target-plane (XTP) measurements for a variety of OMEGA beams (p. 161). Data show that beam-to-beam variation for the UVETP was within acceptable rms variation, while the XTP showed some beams to lie slightly outside the acceptable range.
• R. Adam et al. demonstrate the creation and control of electromagnetic transients through the use of Ta/NiFe/Pt spintronic nanolayers (p. 164). Data suggest the transients’ amplitudes depend linearly on the average laser power illuminating the nanolayers, with blue lasers giving 3× the amplitude compared to an infrared laser for the same power.
• S. G. Demos et al. present laser-damage measurements from illuminating dispersed stainless-steel and titanium particles onto optical surfaces (p. 168). Results showcase three contamination mechanisms following the interaction of the laser pulse with the particles.
• M. Koepke et al. present summary information of the 11th Omega Laser Facility Users Group Workshop (p. 172). Also presented are user Findings and Recommendations to the Omega Laser Facility.
• J. DeGroote Nelson, T. Z. Kosc, and P. C. Nelson detail the contents of the optics suitcase for educational outreach (p. 175). Reusable and giveaway items are included and meant to quickly capture attention of students and encourage them to share with peers what they have learned.
• M. Sharpe, W. T. Shmayda, and K. Glance present measurements of a pressure–composition–temperature (PCT) phase diagram for palladium hydride and palladium deuteride at low temperatures (p. 177). The measured isotherms show an increasing formation of palladium hydride as the temperature is decreased to a maximum of 0.75 hydrogen-to-metal ratio.
• C. Fagan et al. present comparisons of hydrogen absorption for different samples of stainless-steel 316 with Al2O3 coatings (p. 181). Results show that hydrogen absorption was more affected by a reduction of 300-nm to 5-nm surface roughness than by the presence of an Al₂O₃ coating.
• J. Puth, M. Labuzeta, and D. Canning summarize operations of the Omega Laser Facility during the third quarter of FY19