LLE Review 158

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Highlights

This volume of LLE Review 158, covering the period January–March 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:

• D. Turnbull et al. present measurements indicating the presence of super-Gaussian electron distribution functions in laser-heated plasmas consistent with the predictions of Langdon et al. (p. 63). Standard Maxwellian calculations of electron distribution function overpredict power transfer in cross-beam energy transfer compared with the observed super-Gaussian distribution.
• D. Cao et al. present findings on the interpretation of x-ray–inferred electron temperature for direct-drive inertial confinement fusion (ICF) implosions on OMEGA (p. 65). The electron temperature inferred from hard x-ray continuum emission was shown to be an emission-weighted, harmonic mean electron temperature.
• S. C. Miller et al. investigate fuel–shell interface instability growth in warm shell surrogate implosions on OMEGA for different fuel compositions (p. 69). It was found that the hot spot is relatively insensitive to changes in the deuterium:tritium ratio, in accordance with 2-D DRACO simulations.
• A. Kar et al. introduce a method to measure laser-driven shocks using refraction-enhanced x-ray radiography (REXR) at the shock interface (p. 72). REXR provides information during critical moments in shock formation, when velocity interferometers do not provide any information as a result of blanking from x-ray photoionization.
• J. P. Palastro et al. present a white paper detailing opportunities for laser–plasma interactions made possible by emerging technologies (p. 75).Plasma optics, i.e., optical components consisting of plasma with tailored dielectric properties, can provide the disruptive technology to enable high-intensity laser research for decades to come.
• P. M. Nilson et al. present a technique for studying laser-driven magnetic reconnection in the laboratory (p. 84). Proton radiography was used to demonstrate the technique by mapping the changes in magnetic connectivity at the target surface. The data show where the magnetic fields are located, where they are transported, how they merge and reconnect, and where they reside post reconnection.
• A. M. Hansen et al. demonstrate a new method for mitigating self-focusing of probe radiation in Thomson-scattering experiments (p. 87). The Thomson-scattered signal-to-noise ratio can be improved by 10× using a distributed phase plate, effectively distributing the laser’s power across many lower power speckles.
• R. K. Follett et al. define thresholds for absolute laser–plasma instabilities driven by a broadband laser (p. 89). Calculations suggest that the threshold can be increased by 2× with 1.5% bandwidth of the broadband laser.
• A. J. Tu et al. detail a complex ray-tracing and cross-beam energy transfer code for laser-plasma simulations (p. 92). The new algorithm performs calculations 10× faster than previous cross-beam energy transfer codes.
• M. Zaghoo presents new thermodynamic constraints on the mechanical, thermal, and magnetic properties of super-Earth–sized planets (p. 95). The results support the concept of “super-habitability” in which some terrestrial planets have enhanced characteristics suitable for habitability.
• V. V. Karasiev et al. discuss exchange-correlation thermal effects in shocked deuterium (p. 97). Exchange-correlation thermal effects may become important at 0.1 Fermi temperature, where standard density functional theory codes currently consider a temperature-independent exchange correlation functional.
• J. Katz et al. outline a process for the spatiotemporal flat field for gated optical imagers (p. 101). In the fastest gated optical imagers, the gating process is both spatially and temporally dynamic, necessitating quantitative knowledge of the detector sensitivity to compare data recorded at different image positions.
• W. R. Donaldson and A. Consentino demonstrate the co-timing of UV and IR laser pulses on the OMEGA EP Laser System (p. 104). Typical variations are shown to be less than 20 ps in routine laser operation.
• S.-W. Bahk details the current status of chirped-pulse–amplification (CPA) technology and its applications (p. 108). CPA has revolutionized laser technology and opened the way for studying advanced science in large and small laboratories across the world.
• D. Broege and J. Bromage present measurements of heat flow from surface defects in lithium triborate (p. 111). These measurements are the first interferometric measurements of temperature distributions in a nonlinear optic resulting from absorption from a local defect.
• M. Chorel et al. discuss the role of Urbach tail optical absorption in the subpicosecond laser-induced damage threshold (LIDT) of hafnia and silica coatings (p. 113). The results suggest the presence of a correlation between absorption at the Urbach tail to the coating’s intrinsic LIDT at 1053 nm with subpicosecond pulses.
• T. Z. Kosc et al. present a method of measuring angularly dependent spontaneous Raman scattering in crystalline materials (p. 115). This new and flexible configuration makes it possible to measure any crystal cut in any pump or probe configuration.
• D. R. Harding et al. compare shadowgraphy and x-ray phase contrast methods for the characterization of DT ice layers in ICF targets (p. 118). It is shown that x-ray phase contrast provides the best assessment of low-mode roughness, while shadowgraphy provides the best contrast for detecting individual grooves in an ice layer.
• B. S. Rice et al. have developed a method to predict DT ice-layer uniformity in ICF capsules (p. 120). The predictive capability is developed through a multiphase heat-transfer numerical model.
• K. Kopp and S. G. Demos introduce a curriculum for microscopy with ultraviolet surface excitation (MUSE) into a high school science classroom (p. 122). MUSE can eliminate the need for lengthy microscope slide fixation and preparation, providing a far more engaging experience for biology and physics students.
• J. Puth et al. summarize operations of the Omega Laser Facility during the second quarter of the FY19 reporting period (p. 124).