This volume of LLE Review 157, covering the period October–December 2018, 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 using the DOI link provided below.
Additional highlights of research presented in this issue include the following:
- Igumenshchev et al. review the consequences of rarefaction flows on mitigation of laser imprint in direct-drive implosions (p. 1). Rarefaction flows can result in a decay of imprinted modulations during early hydrodynamic evolution. Three-dimensional ASTER simulations were used to demonstrate the mechanism and achieve performance closer to that of 1-D simulations when the implosion develops an after-shock rarefaction flow than in designs without such flow.
- Davies et al. infer the fuel areal density of laser-driven magnetized liner implosions on OMEGA from secondary neutron yields (p. 3). The results broadly indicate discrepancy between 1-D and 2-D simulation predictions and the experimentally measured areal density and convergence ratio.
- Milder et al. present a statistical study on the implications of non-Maxwellian electron velocity distribution functions on the inference of plasma parameters using collective Thomson scattering (p. 6). Small changes in the shape of the distribution function are found to be the limiting factor in the determination of plasma conditions.
- Henchen et al. infer heat flux through laser-produced coronal plasma using collective Thomson scattering (p. 8). The results of the experiment suggest that classical thermal transport theory is not valid in plasma with steep temperature gradients.
- Karasiev et al. present a report on the status of free-energy representations for homogeneous electron gas (p. 10). The equivalence between three global representations of the free energy, the Karasiev–Sjostrom–Dufty–Trickey (KSDT) representation; its descendant, the corrected KSDT; and the Groth–Dornheim–Bonitz parameterization are demonstrated through their correspondence with quantum Monte Carlo results of Dornheim et al.
- An electron spectrometer with multiple viewing angles has been developed for the OMEGA ten-inch–manipulator diagnostic platform (p. 13). Habara et al. discuss how this versatile diagnostic can be deployed on the OMEGA and OMEGA EP Laser Systems.
- Serafini et al. studied the ultrafast optical properties of single-crystal cadmium magnesium telluride for use in x-ray radiation detectors (p. 15). The carrier recombination and trapping components of electronic relaxation are analyzed with a coupled rate-equation model.
- Begishev et al. present the fifth-harmonic conversion of a neodymium glass laser using large-aperture ammonium dihydrogen phosphate (ADP) crystals (p. 18). Phase-matching conditions for the sum-frequency generation are reached by cooling ADP crystals to –70°C.
- Kafka and Demos study the interaction of 10-ps and 0.6-ps laser pulses with microparticles located on the surface of a multi-layer dielectric mirror (p. 21). These findings aid in understanding and assessing the risk of contamination-induced damage in short-pulse laser systems.
- Kosc et al. study the laser-induced–damage threshold for nematic liquid crystals at pulse durations from 600 fs to 1.5 ns (p. 24). Such data provide guidance for future applications in high-power and/or peak intensity laser systems.
- Demos et al. study the dominant mechanisms of laser-induced damage in optical materials with 355-nm, +1-ns pulses (p. 27). The study finds two damage pathways for the optical material, arising from self-focusing, which is caused by refractive index change from electron energy transition in the material, and from local intense heating causing above-melting temperatures near the surface of the material.
- Shmayda et al. present a process for extracting tritium from contaminated water using combined electrolysis and catalytic exchange (p. 30). This process provides an economical and robust form of tritium recovery.
- Sharpe et al. quantify the distribution of tritium in the near surface of stainless-steel alloy 316 (p. 33). Such measurements inform understanding of tritium migration through stainless steel with implications for decontamination.
- Ghosh et al. present cathodic electrolytic deposition used to synthesize nanoscale copper-hydroxyapatite coatings for antibacterial implants (p. 36). Results show the copper nanoparticles reduced numbers of E. Coli and S. aureus by 78% and 83%, respectively.
- Zhang et al. study the effect of heat treatment of silver hydroxyapatite coatings on the antibacterial properties of the coating (p. 38). The results demonstrate that heat treatment enhances the antibacterial coating and reduces variability.
- Koroliov et al. use terahertz time-domain spectroscopy (THz-TDS) to characterize graphene nanofiller within nanocomposite materials (p. 40). The THz-TDS method probes the dielectric properties of the sample, providing global information regarding the dispersion of graphene and its in-situ electronic quality.
- Kruschwitz et al. present a wavelength-tunable ultraviolet beam on OMEGA EP (p. 43). This upgrade allows experiments to characterize the interaction of the tunable beam with one or more fixed-wavelength beams on OMEGA.
- In order to characterize on-shot conditions, LLE has built a full-beam-in-tank (FBIT) diagnostic to characterize the OMEGA focal spot. Waxer et al. discuss how these results provide a measure of the on-shot laser uniformity on target from data collected inside the target chamber (p. 46).
- Bauer et al. compare results from FBIT data to equivalent-target-plane (ETP) measurements for the OMEGA focal spot (p. 49). Preliminary data suggest that upstream diagnostics such as the ETP compare closely with the results found using FBIT.
- Sampat et al. report on efforts to achieve power balance requirements for OMEGA to less than 1% rms (p. 52). Management of saturation in the stage-E and F amplifiers is shown to provide control of beam power while maintaining the requested pulse shape.
- Puth et al. summarize operations of the Omega Laser Facility during the first quarter of the FY19 reporting period (p. 54).
- Frenje et al. present a study of stopping power for low-Z materials near the Bragg peak (p. 56). Data show good agreement in most cases for electron–ion Coulomb scattering except for DD-t, which is postulated to depend more strongly on ion–ion nuclear elastic scattering than predicted.
- Sio et al. measure the relative timing between the nuclear reaction history of different fuel-ion (D, T, 3He) populations using a particle x-ray temporal diagnostic (p. 59). The observed rate histories are more closely represented with a kinetic-ion model as compared with average-ion fluid models.