Stochastic homogenization of the laser intensity to improve the irradiation uniformity of capsules directly driven by thousands laser beams

Illumination uniformity of a spherical capsule directly driven by laser beams has been assessed numerically. Laser facilities characterized by ND = 12, 20, 24, 32, 48 and 60 directions of irradiation with associated a single laser beam or a bundle of NB laser beams have been considered. The laser beam intensity profile is assumed super-Gaussian and the calculations take into account beam imperfections as power imbalance and pointing errors. The optimum laser intensity profile, which minimizes the root-mean-square deviation of the capsule illumination, depends on the values of the beam imperfections. Assuming that the NB beams are statistically independents is found that they provide a stochastic homogenization of the laser intensity associated to the whole bundle, reducing the errors associated to the whole bundle by the factor  , which in turn improves the illumination uniformity of the capsule. Moreover, it is found that the uniformity of the irradiation is almost the same for all facilities and only depends on the total number of laser beams Ntot = ND × NB

Direct spectrum of the benchmark t dwarf HD 19467 B

This is the final version of the article. Available from the American Astronomical Society / IOP Publishing via the DOI in this record.HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R ≈ 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 ± 1 dwarf with effective temperature Teff = 978+20 -43 K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.The TrenDS high-contrast imaging program is supported by NASA Origins of Solar Systems grant NNX13AB03G and the NASA Early Career Fellowship program. A portion of this work was supported by the National Science Foundation under Grant Numbers AST-0215793, 0334916, 0520822, 0804417 and 1245018. This work was partially supported by NASA ADAP grant 11-ADAP11-0169 and NSF award AST 1211568. A portion of the research in this Letter was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. J.A. is supported by the National Physical Science Consortium. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by Adam Burgasser.1

Project 1640 Observations of Brown Dwarf GJ 758 B: Near-infrared Spectrum and Atmospheric Modeling

The nearby Sun-like star GJ 758 hosts a cold substellar companion, GJ 758 B, at a projected separation of $\lesssim$30 AU, previously detected in high-contrast multi-band photometric observations. In order to better constrain the companion's physical characteristics, we acquired the first low-resolution ($R \sim 50$) near-infrared spectrum of it using the high-contrast hyperspectral imaging instrument Project 1640 on Palomar Observatory's 5-m Hale telescope. We obtained simultaneous images in 32 wavelength channels covering the $Y$, $J$, and $H$ bands ($\sim$952-1770 nm), and used data processing techniques based on principal component analysis to efficiently subtract chromatic background speckle-noise. GJ 758 B was detected in four epochs during 2013 and 2014. Basic astrometric measurements confirm its apparent northwest trajectory relative to the primary star, with no clear signs of orbital curvature. Spectra of SpeX/IRTF observed T dwarfs were compared to the combined spectrum of GJ 758 B, with ${\chi}^2$ minimization suggesting a best fit for spectral type T7.0$\pm$1.0, but with a shallow minimum over T5-T8. Fitting of synthetic spectra from the BT-Settl13 model atmospheres gives an effective temperature $T_{\text{eff}}=741 \pm 25$ K and surface gravity $\log g = 4.3 \pm 0.5$ dex (cgs). Our derived best-fit spectral type and effective temperature from modeling of the low-resolution spectrum suggest a slightly earlier and hotter companion than previous findings from photometric data, but do not rule out current results, and confirm GJ 758 B as one of the coolest sub-stellar companions to a Sun-like star to date

Ignition conditions for inertial confinement fusion targets with a nuclear spin-polarized DT fuel

The nuclear fusion cross-section is modified when the spins of the interacting nuclei are polarized. In the case of deuterium?tritium it has been theoretically predicted that the nuclear fusion cross-section could be increased by a factor d = 1.5 if all the nuclei were polarized. In inertial confinement fusion this would result in a modification of the required ignition conditions. Using numerical simulations it is found that the required hot-spot temperature and areal density can both be reduced by about 15% for a fully polarized nuclear fuel. Moreover, numerical simulations of a directly driven capsule show that the required laser power and energy to achieve a high gain scale as d-0.6 and d-0.4 respectively, while the maximum achievable energy gain scales as d0.9

Comparison of capsule deformations induced by radiation asymmetries in spherical and cylindrical hohlraums lighted by the laser MégaJoule

The nominal configuration of inertial confinement fusion with the Laser MégaJoule (LMJ) uses a cylindrical hohlraum with two polar holes for the entrance of 60 laser quads. But the LMJ facility makes it possible to use a spherical hohlraum with more than two holes. We have studied two alternate configurations, in which 56 and 44 laser quads enter a spherical hohlraum through four and six holes respectively, with the same wall surface as in the nominal cylindrical hohlraum. We have estimated the intrinsic and random radiation asymmetries on the nominal capsule A1040 in these two configurations

A critical comparison of several numerical methods for computing effective properties of highly heterogeneous materials

Modelling transport and long-term creep in concrete materials is a difficult problem when the complexity of the microstructure is taken into account, because it is hard to predict instantaneous elastic responses. In this work, several numerical methods are compared to assess their properties and suitability to model concrete-like microstructures with large phase properties contrast. The methods are classical finite elements, a novel extended finite element method (μ-xfem), an unconstrained heuristic meshing technique (amie), and a locally homogenising preprocessor in combination with various solvers (benhur). The benchmark itself consists of a number of simple and complex microstructures, which are tested with a range of phase contrasts designed to cover the needs of creep and transport modelling in concrete. The calculations are performed assuming linear elasticity and thermal conduction. The methods are compared in term of precision, ease of implementation and appropriateness to the problem type. We find that xfem is the most suitable when the mesh if coarse, and methods based on Cartesian grids are best when a very fine mesh can be used. Finite element methods are good compromises with high flexibility. © 2013 Elsevier Ltd. All rights reserved

Etude de la variance sur la temperature en photonique Monte-Carlo

SIGLECNRS RP 148 (706) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Review of the Current State of Knowledge on the Effects of Radiation on Concrete

A review of the current state of knowledge on the effects of radiation on concrete in nuclear power production applications is presented. Emphasis is placed on the effects of radiation damage, as reflected by changes in engineering properties of concrete, in the evaluation of the long-term operation and for plant life or aging management of nuclear power plants (NPPs) in Japan, Spain, and the United States. National issues and concerns are described for Japan and the United States followed by a discussion of the fundamental understanding of the effects of radiation on concrete. Specifically, the effects of temperature, moisture content, and irradiation on ordinary Portland cement paste and the role of temperature and neutron energy spectra on radiation-induced volumetric expansion (RIVE) of aggregate-forming minerals are described. This is followed by a discussion of the bounding conditions for extended operation; the significance of accelerated irradiation conditions; the role of temperature and creep; and how these issues are being incorporated into numerical and meso-scale models. From these insights on radiation damage, analyses of these effects on concrete structures are reviewed, and the current status of work in Japan and the United States is described. Also discussed is the recent formation of a new international scientific and technical organization, the International Committee on Irradiated Concrete, to provide a forum for timely information exchanges among organizations pursuing the identification, quantification, and modeling of the effects of radiation on concrete in commercial nuclear applications. The paper concludes with a discussion of research gaps, including (1) interpreting test-reactor data, (2) evaluating service-irradiated concrete for aging management and to inform radiation damage models with the Zorita NPP (Spain) serving as the first comprehensive test case, (3) irradiated-assisted alkali-silica reactions, and (4) RIVE under constrained conditions.The authors gratefully thank the following sponsors: US DOE, Office of Nuclear Energy, Light Water Reactor Sustainability Program (TMR, YLP, ABG, and IR); the Nuclear Regulation Authority, Japan (IM and OK); the EPRI Long Term Operations Program (JJW); the US NRC (MS); Consejo de Seguridad Nuclear (CA and MO); IETcc-CSIC (CA); and ENRESA (MO) for support of work on the effects of radiation on concrete