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Chen, B.

Publications and source records attributed to Chen, B..

32 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Progress towards modeling tokamak boundary plasma turbulence and understanding its role in setting divertor heat flux widths

The heat flux distributions on divertor targets in H-mode plasmas are grave concerns for future devices. We seek to simulate the tokamak boundary plasma turbulence and heat transport in the edge localized mode-suppressed regimes. The improved BOUT++ model shows that not only I p but also the radial electric field E r plays a crucial role on the turbulence behavior and sets the heat flux width. Instead of calculating E r from the pressure gradient term (diamagnetic E r ), it is measured from the plasma transport equations with the sheath potential in the scrape-off layer and the plasma density and temperature profiles inside the separatrix from the experiment. The simulation results with the new E r model have better agreement with the experiment than using the diamagnetic Er model: (1) The electromagnetic turbulence in enhanced D α H-mode shows the characteristics of quasi-coherent modes (QCMs) and broadband turbulence. The mode spectra are in agreement with the phase contrast imaging data and almost has no change in comparison to the cases which use the diamagnetic Er model; (2) the self-consistent boundary E r is needed for the turbulence simulations to get the consistent heat flux width with the experiment; (3) the frequencies of the QCMs are proportional to E r , while the divertor heat flux widths are inversely proportional to Er; and (4) the BOUT++ turbulence simulations yield a similar heat flux width to the experimental Eich scaling law and the prediction from the Goldston heuristic drift model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Effect of Ni content on the microstructure and mechanical properties of weld metal with both-side submerged arc welding technique

Highlights: • This manuscript primarily studied the effects of Ni content on the K65 weld metals; • Increase Ni content could significantly improve the strength and low temperature impact toughness of the weld metal. • The beneficial effect of Ni is attributed to its positive effect on phase transformation. • GBF keeps K-S or N-W relations only with one austenite and the variants belong to the same bain group are two reasons. • The M/A islands are considered to be another reason for the reduced toughness. - Abstract: The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Here, imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense matter studies of micrometer-sized samples in laser-plasma experiments.

42 ENGINEERING↗
DOE OSTI2017

Edge turbulence and divertor heat flux width simulations of Alcator C-Mod discharges using an electromagnetic two-fluid model

The BOUT++ code has been utilized in order to improve the understanding of the role of turbulent modes in controlling edge transport and resulting scaling of the scrape-off layer (SOL) heat flux width. For the C-Mod enhanced D α (EDA) H-mode discharges, BOUT++ six-field two-fluid nonlinear simulations show a reasonable agree- ment of upstream turbulence and divertor target heat flux behavior: a) The simulated quasi-coherent modes (QCMs) show consistent characteristics of the frequency versus poloidal wave number spectra of the electromagnetic fluctuations when compared with experimental measurements: frequencies are around 60-120 kHz (experiment: about 70-110 kHz), k θ are around 2.0 cm ₋1 which is similar to the Phase Contrast Imaging data; b) Linear spectrum analysis is consistent with the nonlinear phase relationship cal- culation which indicates the dominance of resistive-ballooning modes and drift-Alfven wave instabilities; c) The SOL heat flux width λ q vs current I p scaling is reproduced by turbulent transport: the simulations yield similar λ q to experimental measurements within a factor of 2. Yet the magnitudes of divertor heat fluxes can be varied, depending on the physics models, sources and sinks, sheath boundary conditions, or flux limiting coefficient; d) Simple estimate by the "2-point model" for λ q is consistent with simulation. Moreover, blobby turbulent spreading is confirmed for these relatively high B p shots.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Accelerating gravitational microlensing simulations using the Xeon Phi coprocessor

Recently Graphics Processing Units (GPUs) have been used to speed up very CPU-intensive gravitational microlensing simulations. In this work, we use the Xeon Phi coprocessor to accelerate such simulations and compare its performance on a microlensing code with that of NVIDIA's GPUs. For the selected set of parameters evaluated in our experiment, we find that the speedup by Intel's Knights Corner coprocessor is comparable to that by NVIDIA's Fermi family of GPUs with compute capability 2.0, but less significant than GPUs with higher compute capabilities such as the Kepler. However, the very recently released second generation Xeon Phi, Knights Landing, is about 5.8 times faster than the Knights Corner, and about 2.9 times faster than the Kepler GPU used in our simulations. Here, we conclude that the Xeon Phi is a very promising alternative to GPUs for modern high performance microlensing simulations. LESS

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Procedures for cryogenic X-ray ptychographic imaging of biological samples

Biological sample-preparation procedures have been developed for imaging human chromosomes under cryogenic conditions. A new experimental setup, developed for imaging frozen samples using beamline I13 at Diamond Light Source, is described. This manuscript describes the equipment and experimental procedures as well as the authors' first ptychographic reconstructions using X-rays.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Direct optical transitions at K- and H-point of Brillouin zone in bulk MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2}

Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2}. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at K point, and therefore, direct optical transitions at H point should be expected in modulated reflectance spectra besides the direct optical transitions at the K point of Brillouin zone. This prediction is confirmed by experimental studies of the electronic band structure of MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2} crystals by CER, PR, and PzR spectroscopy, i.e., techniques which are very sensitive to critical points of Brillouin zone. For the four crystals besides the A transition at K point, an A{sub H} transition at H point has been observed in CER, PR, and PzR spectra a few tens of meV above the A transition. The spectral difference between A and A{sub H} transition has been found to be in a very good agreement with theoretical predictions. The second transition at the H point of Brillouin zone (B{sub H} transition) overlaps spectrally with the B transition at K point because of small energy differences in the valence (conduction) band positions at H and K points. Therefore, an extra resonance which could be related to the B{sub H} transition is not resolved in modulated reflectance spectra at room temperature for the four crystals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2006

The Origin of Systematic Errors in the GCM Simulation of ITCZ Precipitation

Previous GCM studies have found that the systematic errors in the GCM simulation of the seasonal mean ITCZ intensity and location could be substantially corrected by adding suitable amount of rain re-evaporation or cumulus momentum transport. However, the reason(s) for these systematic errors and solutions has remained a puzzle. In this work the knowledge gained from previous studies of the ITCZ in an aqua-planet model with zonally uniform SST is applied to solve this puzzle. The solution is supported by further aqua-planet and full model experiments using the latest version of the Goddard Earth Observing System GCM.

Chao, Winston C.↗
NASA NTRS1998

Evaluation of radiation effects against C6 glioma in combination with vaccinia virus-p53 gene therapy

The primary objective of this study was to evaluate the antitumor effects of recombinant vaccinia virus-p53 (rVV-p53) in combination with radiation therapy against the C6 rat glioma, a p53 deficient tumor that is relatively radioresistant. VV-LIVP, the parental virus (Lister strain), was used as a control. Localized treatment of subcutaneous C6 tumors in athymic mice with either rVV-p53 or VV-LIVP together with tumor irradiation resulted in low tumor incidence and significantly slower tumor progression compared to the agents given as single modalities. Assays of blood and spleen indicated that immune system activation may account, at least partly, for the enhance tumor inhibition seen with combined treatment. No overt signs of treatment-related toxicity were noted.

NASA Discipline Radiation Health↗
NASA NTRS1992

Extracting galactic structure parameters from multivariated density estimation

Multivariate statistical analysis, including includes cluster analysis (unsupervised classification), discriminant analysis (supervised classification) and principle component analysis (dimensionlity reduction method), and nonparameter density estimation have been successfully used to search for meaningful associations in the 5-dimensional space of observables between observed points and the sets of simulated points generated from a synthetic approach of galaxy modelling. These methodologies can be applied as the new tools to obtain information about hidden structure otherwise unrecognizable, and place important constraints on the space distribution of various stellar populations in the Milky Way. In this paper, we concentrate on illustrating how to use nonparameter density estimation to substitute for the true densities in both of the simulating sample and real sample in the five-dimensional space. In order to fit model predicted densities to reality, we derive a set of equations which include n lines (where n is the total number of observed points) and m (where m: the numbers of predefined groups) unknown parameters. A least-square estimation will allow us to determine the density law of different groups and components in the Galaxy. The output from our software, which can be used in many research fields, will also give out the systematic error between the model and the observation by a Bayes rule.

Chen, B.↗
NASA NTRS1982

Integrated optics technology study

The materials and processes available for the fabrication of single mode integrated electrooptical components are described. Issues included in the study are: (1) host material and orientation, (2) waveguide formation, (3) optical loss mechanisms, (4) wavelength selection, (5) polarization effects and control, (6) laser to integrated optics coupling,(7) fiber optic waveguides to integrated optics coupling, (8) souces, (9) detectors. The best materials, technology and processes for fabrication of integrated optical components for communications and fiber gyro applications are recommended.

Chen, B.↗
NASA NTRS1982

Integrated optics technology study

The status and near term potential of materials and processes available for the fabrication of single mode integrated electro-optical components are discussed. Issues discussed are host material and orientation, waveguide formation, optical loss mechanisms, wavelength selection, polarization effects and control, laser to integrated optics coupling fiber optic waveguides to integrated optics coupling, sources, and detectors. Recommendations of the best materials, technology, and processes for fabrication of integrated optical components for communications and fiber gyro applications are given.

Chen, B.↗