Optical and structural properties of GaSb and Te-doped GaSb single crystals are reported herein. Utilizing the photoreflectance technique, the band gap energy for doped samples was obtained at 0.814
...eV. Photoluminescence (PL) spectra showed a peak at 0.748
eV that according to this research, belongs to electronic states of pure GaSb and not to the longitudinal optical (LO) phonon replica as has been reported by other authors. Analysis of the full width at half maximum (FWHM) values of X-ray diffraction, as well as micro-Raman peaks showed that the inclusion of Te decreases the crystalline quality.
In this work a multibody collision model, ame-nable to large-scale computation, is developed to simulate material removal with particulate flows. This model is developed by computing momentum ...exchange to account for different force interactions: (1) particle–particle interaction, (2) particle–fluid interaction, and (3) particle–surface interaction. For the particle-fluid interaction, a velocity field for the fluid is assumed to be known, and the drag force on the particles is computed from this field. In the particle–surface interaction, the Boussinesq solution for a point load on an elastic half-space is used along with the von-Mises yield criterion to determine the amount of material removed. Employing this model, inverse problems are then constructed where combinations of the abrasive particle size, the particle size distribution, the flow velocity, etc., are sought to maximize the efficiency of the process. A genetic algorithm is used to treat this inverse problem, and numerical examples are given to illustrate the overall approach.
Harmonic sextupoles for the Advanced Light Source low emittance upgrade Madur, A.; Arbelaez, D.; Marks, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2011, Letnik:
649, Številka:
1
Journal Article
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The Advanced Light Source is a 3rd generation light source in operation since 1993. This light source is providing state of the art performance to more than 40 beamlines and their users thanks to the ...upgrades that have been completed over the last few years. Higher photon beam brightness is expected to become available to users in the near future through a new upgrade with the introduction of 48 sextupoles in the ALS lattice. Introducing new combined function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. Moreover, the existing steering magnets will be replaced by the harmonic sextupoles. Therefore predicting the hysteresis behavior of the harmonic sextupole steering functions became critical for those included in the fast-orbit feedback loop (22 of them). After a brief introduction to the motivation for the upgrade and the scope of the project, we develop in this paper the different constraints driving the three required combined function magnet designs as well as their expected performance.
We present the design of a four-layer, Canted Cosine Theta (CCT) Nb<inline-formula><tex-math notation="LaTeX">_3</tex-math></inline-formula>Sn dipole magnet as part of the general R&D program for ...high field superconducting magnets supported by the US Magnet Development Program (US-MDP). Future testing with High-Temperature Superconducting (HTS) inserts in a hybrid configuration motivates the design's large clear aperture of 120 mm and target operating dipole field of 12 T at 4.2 K. First, we present a graded magnetic design utilizing existing Nb<inline-formula><tex-math notation="LaTeX">_3</tex-math></inline-formula>Sn cables which results in 30% operating current margin at the target field. We then share results from a 2D mechanical analysis which makes use of an idealized external structure to provide initial guidance for design studies. This mechanical analysis is extended to demonstrate compatibility of the CCT6 design with a mechanical support structure, based on key and bladder technology, currently considered for use within multiple US-MDP high-field magnet programs.
A high-performance superconducting undulator concept, incorporating stacked YBa 2 Cu 3 O 7-δ (YBCO) tapes operating at 4.2 K, is currently under investigation at LBNL as one of many technology ...options for future FEL applications. The concept is particularly promising for narrow-gap, short period (<;10 mm) regimes, where traditional superconducting and permanent magnet technologies are less-suited. The current path is dictated by etching the YBCO layer using lithography techniques, resulting in a high degree of uniformity from tape to tape as well as a straightforward and highly cost-effective means of production. We describe the approaches being pursued for the tape preparation and the conceptual design of a device. We also provide an initial analysis of the impact of fabrication tolerances in terms of field errors for FEL application.
Hard coatings are continuously improved due to the industrial needs and urgency to reduce the environmental impact of manufacturing processes. For these reasons, scientists seek hard coatings ...resistant to high mechanical and thermal loads under extreme working conditions (i.e., dry machining), which is why Hf and other rare earth metals have been added to the metastable c-AlxTi(1-x)N nitrides. In the present investigation, Hf-doped c-Al0.64Ti0.36N was deposited in a 2- & 3-axis rotation system using a semi-industrial coater. For this purpose Hf-pins were fixed in Al/Ti targets that produced coatings with ~0.2 at. % Hf-contents homogeneously dispersed. Hf effect on the crystalline state and microstructure, mechanical properties, high-temperature resistance, and the tribological performance of the coating in an Ar-jet at 900 °C were analyzed. It was found that the Hf-doped Al0.64Ti0.36N 5.07 μm thick-layer was mainly cubic fcc + traces of the hcp phases and displayed higher mean hardness (36 GPa) and E-module (416 GPa) than the coating without Hf (h = 32 GPa and E = 402 Pa). The Hf-containing nitride oxidizes dynamically during the high-temperature tribology testing and produces t-Ti2O3 & o-Al2TiO5 after short exposure periods (2.5–5 min), which strongly affected the CoF, before evolving to thermodynamically stable α-Al2O3 & anatase TiO2 between 10 & 30 min in the Ar-flow, thus resulting in the relative stability of the CoF. The mechanical evaluation of the oxidized coatings indicates that a specific oxide thickness must be reached to avoid catastrophic system damage at high normal loads.
•Hf-doped c-Al0.66Ti0.34N coating was deposited in a semi-industrial PVD coater.•0.2 at. % Hf is enough to improve hardness and E-module of arc PVD c-Al0.66Ti0.34N.•t-Ti2O3 & o-Al2TiO5 are built (<5 min) and evolve to α-Al2O3 & a-TiO2 (>30 min) in an Ar-jet at 900 °C.•Fragile unstable oxides are affecting the high-temperature tribology of c-Al0.638Ti0.36Hf0.002N coatings.•The oxides generated at 900 °C modify the stiffness of the coating-substrate system.
We present the design of a four-layer, Canted Cosine Theta (CCT) NbFormula OmittedSn dipole magnet as part of the general R&D program for high field superconducting magnets supported by the US Magnet ...Development Program (US-MDP). Future testing with High-Temperature Superconducting (HTS) inserts in a hybrid configuration motivates the design’s large clear aperture of 120 mm and target operating dipole field of 12 T at 4.2 K. First, we present a graded magnetic design utilizing existing NbFormula OmittedSn cables which results in 30% operating current margin at the target field. We then share results from a 2D mechanical analysis which makes use of an idealized external structure to provide initial guidance for design studies. This mechanical analysis is extended to demonstrate compatibility of the CCT6 design with a mechanical support structure, based on key and bladder technology, currently considered for use within multiple US-MDP high-field magnet programs.
An experimental-numerical methodology for failure analysis of the c-Al0.66Ti0.34N/Interface/M2 steel coating system is proposed here. This c-Al0.66Ti0.34N coating was deposited by the arc-PVD ...technique. The values of the elastic modulus, the fracture energy release rate and the nano-hardness of the coating were obtained by nanoindentation. Normal and shear stress limits of the interface, as well as the adhesive and cohesive critical loads, were measured with the scratch test method. A finite element analysis, using the experimental mechanical properties, was carried out to understand the relationship between the irreversible work vs. depth curve and the mechanical failure evolution of the coating-substrate system, associating the pop-in with nucleation, crack growth and cracking pattern. Extended finite element method (XFEM) was applied for modeling of the mechanical behavior of the coating; the cohesive zones approach was applied for modeling the interface and the Ramberg-Osgood law for modeling the substrate. This approach proposes an experimental-numerical methodology for failure analysis of hard coatings (monolithic body) allowing to calculate fracture energy of the coating material and to model cracking patterns caused by contact mechanics. This work is the first step to answer questions about multi-scale approaches for multi-functional multi-layer coatings to push their enhancements and further applications.
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•Experimental-numerical XFEM + CZM approach for understanding the hard coatings failure•The irreversible work vs. depth curve is related to the cracking mechanism.•Elastoplastic deformation energy translate into crack nucleation and opening.•Correlation between the irreversible work and the modeled cracking patterns is attain.•The XFEM + CZM methodology is validated through the morphology of ring cracks.
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