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DOE OSTI2013

Phonon-limited low-field mobility in silicon: Quantum transport vs. linearized Boltzmann Transport Equation

We propose to check and validate the approximations made in dissipative quantum transport (QT) simulations solved in the Non-equilibrium Green's Function formalism by comparing them with the exact solution of the linearized Boltzmann Transport Equation (LB) in the stationary regime. For that purpose, we calculate the phonon-limited electron and hole mobility in bulk Si and ultra-scaled Si nanowires for different crystal orientations 〈100〉, 〈110〉, and 〈111〉. In both QT and LB simulations, we use the same sp{sup 3}d{sup 5}s{sup *} tight-binding model to describe the electron/hole properties and the same valence-force-field approach to account for the phonon properties. It is found that the QT simplifications work well for electrons, but are less accurate for holes, where a renormalization of the phonon scattering strength is proved useful to improve the results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2013

Application of MMC model on simulation of shearing process of thick hot-rolled high strength steel plate

Shear operation is widely used as the first step in sheet metal forming to cut the sheet or plate into the required size. The shear of thick hot-rolled High Strength Steel (HSS) requires large shearing force and the sheared edge quality is relatively poor because of the large thickness and high strength compared with the traditional low carbon steel. Bad sheared edge quality will easily lead to edge cracking during the post-forming process. This study investigates the shearing process of thick hot-rolled HSS plate metal, which is generally exploited as the beam of heavy trucks. The Modified Mohr-Coulomb fracture criterion (MMC) is employed in numerical simulation to calculate the initiation and propagation of cracks during the process evolution. Tensile specimens are designed to obtain various stress states in tension. Equivalent fracture strains are measured with Digital Image Correlation (DIC) equipment to constitute the fracture locus. Simulation of the tension test is carried out to check the fracture model. Then the MMC model is applied to the simulation of the shearing process, and the simulation results show that the MMC model predicts the ductile fracture successfully.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Production of high intensity {sup 48}Ca for the 88-Inch Cyclotron and other updates

Recently the Versatile ECR for NUclear Science (VENUS) ion source was engaged in a 60-day long campaign to deliver high intensity {sup 48}Ca{sup 11+} beam to the 88-Inch Cyclotron. As the first long term use of VENUS for multi-week heavy-element research, new methods were developed to maximize oven to target efficiency. First, the tuning parameters of VENUS for injection into the cyclotron proved to be very different than those used to tune VENUS for maximum beam output of the desired charge state immediately following its bending magnet. Second, helium with no oxygen support gas was used to maximize the efficiency. The performance of VENUS and its low temperature oven used to produce the stable requested 75 eμA of {sup 48}Ca{sup 11+} beam current was impressive. The consumption of {sup 48}Ca in VENUS using the low temperature oven was checked roughly weekly, and was found to be on average 0.27 mg/h with an ionization efficiency into the 11+ charge state of 5.0%. No degradation in performance was noted over time. In addition, with the successful operation of VENUS the 88-Inch cyclotron was able to extract a record 2 pμA of {sup 48}Ca{sup 11+}, with a VENUS output beam current of 219 eμA. The paper describes the characteristics of the VENUS tune used for maximum transport efficiency into the cyclotron as well as ongoing efforts to improve the transport efficiency from VENUS into the cyclotron. In addition, we briefly present details regarding the recent successful repair of the cryostat vacuum system.

43 PARTICLE ACCELERATORS↗

DOE OSTI2013

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

The nature and level of turbulent transport in the outer core of low-confinement (L-mode) discharges performed at the ASDEX Upgrade tokamak [Kallenbach et al., Nucl. Fusion 51, 094012 (2011)] are examined. Previously, it was found that for an L-mode discharge of the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] gyrokinetic simulations were unable to reproduce the experimental ion heat flux, underestimating it by almost an order of magnitude. In the present work, employing the GENE gyrokinetic turbulence code, an extensive nonlinear study is performed for L-mode discharges of ASDEX Upgrade in order to cross-check this observation. It is shown that no systematic underprediction can be found in these simulations—instead, discrepancies with respect to experimental transport levels are small enough to be resolved within the uncertainties of the experimental profiles. Moreover, it is shown that some turbulence properties resemble closely those of the underlying linear microinstabilities at least out to 90% of the minor radius, so that quasilinear transport models remain, in principle, applicable even for these parameters, provided that appropriate nonlinear saturation rules can be developed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Tests of by-pass diodes at cryogenic temperatures for the KATRIN magnets

The Karlsruhe Tritium Neutrino experiment (KATRIN) requires a series of superconducting solenoid magnets for guiding beta-electrons from the source to the detector. By-pass diodes will operate at liquid helium temperatures to protect the superconducting magnets and bus bars in case of quenches. The operation conditions of the by-pass diodes depend on the different magnet systems of KATRIN. Therefore, different diode stacks are designed with adequate copper heat sinks assuming adiabatic conditions. The by-pass diode stacks have been submitted to cold tests both at liquid nitrogen and liquid helium temperatures for checking operation conditions. This report presents the test set up and first results of the diode characteristics at 300 K and 77 K, as well as of endurance tests of the diode stacks at constant current load at 77 K and 4.2 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Design parameters and commissioning of vertical inserts used for testing the XFEL superconducting cavities

The European XFEL is a new research facility currently under construction at DESY in the Hamburg area in Germany. From 2015 on, it will generate extremely intense X-ray flashes that will be used by researchers from all over the world. The superconducting XFEL linear accelerator consists of 100 accelerator modules with more than 800 RF-cavities inside. The accelerator modules, superconducting magnets and cavities will be tested in the accelerator module test facility (AMTF). This paper gives an overview of the design parameters and the commissioning of the vertical insert, used in two cryostats (XATC) of the AMTF-hall. The Insert serves as a holder for 4 nine-cell cavities. This gives the possibility to cool down 4 cavities to 2K in parallel and, consequently, to reduce the testing time. The following RF measurement, selected as quality check, will be done separately for each cavity. Afterwards the cavities will be warmed up again and will be sent to the accelerator module assembly.

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Performance of a superconducting magnet system operated in the Super Omega Muon beam line at J-PARC

A superconducting magnet system, which is composed of an 8 m long solenoid for transportation and 12 short solenoids for focusing, has been developed for Muon Science Establishment facility of J-PARC. The transport solenoid is composed of a 6 m straight section connected to a 45 degree curved section at each end. Muons of various momenta and of both electric charges are transported through the solenoid inner bore with an effective diameter of 0.3 m, where 2 T magnetic field is induced. There are 12 focusing solenoids with an effective bore diameter of 0.6 m and a length of 0.35 m arranged on a straight line at suitable intervals. The maximum central field of each focusing solenoid is 0.66 T. All solenoid coils are cooled by GM cryocoolers through their own conductions. The magnet system has been installed into the beam line in the summer of 2012, and its performance has been checked. Beam commissioning has been carried out since October 2012. During beam operation, temperature rise over 6 K in the transport solenoid due to a nuclear heating from the muon production target is observed at beam intensity of about 300 kW.

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Cluster synchronization in networks of neurons with chemical synapses

In this work, we study the cluster synchronization of chemically coupled and generally formulated networks which are allowed to be nonidentical. The sufficient condition for the existence of stably synchronous clusters is derived. Specifically, we only need to check the stability of the origins of m decoupled linear systems. Here, m is the number of subpopulations. Examples of nonidentical networks such as Hindmarsh-Rose (HR) neurons with various choices of parameters in different subpopulations, or HR neurons in one subpopulation and FitzHugh-Nagumo neurons in the other subpopulation are provided. Explicit threshold for the coupling strength that guarantees the stably cluster synchronization can be obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Coexistence of considerable inter-particle interactions and spin-glass behavior in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} nanoparticles

We have studied the magnetic and spin-glass (SG) properties of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (t{sub m}). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (T{sub f}) appearing on the real part curve of the ac susceptibility, χ′(T). The T{sub f} value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔT{sub f}/T{sub f}Δ(log{sub 10}f), and the power law τ = τ{sub 0}(T/T{sub g} − 1){sup −zν}. The obtained values of c ≈ 5 × 10{sup −2}, τ{sub 0} ≈ 10{sup −5} s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at T{sub g} below T{sub f}, which decreases with decreasing 〈D〉. Basing on ln(f) versus T{sub f} data, and the Néel-Arrhenius model [ln(f) = ln(f{sub 0}) - E{sub a}/k{sub B}T] and Vogel–Fulcher law [ln(f) = ln(f{sub 0}) - E{sub a}/k{sub B}(T - T{sub 0})], the Larmor frequency (f{sub 0}), activation energy (E{sub a}) and effective temperature (T{sub 0}) for the samples with different 〈D〉 were determined. Obtained results indicate the existence a strong interaction between nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Molecular properties of excited electronic state: Formalism, implementation, and applications of analytical second energy derivatives within the framework of the time-dependent density functional theory/molecular mechanics

This work extends our previous works [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011); J. Liu and W. Z. Liang, J. Chem. Phys. 135, 184111 (2011)] on analytical excited-state energy Hessian within the framework of time-dependent density functional theory (TDDFT) to couple with molecular mechanics (MM). The formalism, implementation, and applications of analytical first and second energy derivatives of TDDFT/MM excited state with respect to the nuclear and electric perturbations are presented. Their performances are demonstrated by the calculations of adiabatic excitation energies, and excited-state geometries, harmonic vibrational frequencies, and infrared intensities for a number of benchmark systems. The consistent results with the full quantum mechanical method and other hybrid theoretical methods indicate the reliability of the current numerical implementation of developed algorithms. The computational accuracy and efficiency of the current analytical approach are also checked and the computational efficient strategies are suggested to speed up the calculations of complex systems with many MM degrees of freedom. Finally, we apply the current analytical approach in TDDFT/MM to a realistic system, a red fluorescent protein chromophore together with part of its nearby protein matrix. The calculated results indicate that the rearrangement of the hydrogen bond interactions between the chromophore and the protein matrix is responsible for the large Stokes shift.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Guidelines for internal optics optimization of the ITER EC H and CD upper launcher

The importance of localized injection of Electron Cyclotron waves to control Magneto-HydroDynamic instability is well assessed in tokamak physics and the set of four Electron Cyclotron (EC) Upper Launchers (UL) in ITER is mainly designed for this purpose. Each of the 4 ULs uses quasi-optical mirrors (shaping and planes, fixed and steerable) to redirect and focus 8 beams (in two rows, with power close to 1 MW per beam coming from the EC transmission lines) in the plasma region where the instability appears. Small beam dimensions and maximum beam superposition guarantee the necessary localization of the driven current. To achieve the goal of MHD stabilization with minimum EC power to preserve the energy confinement in the outer half of the plasma cross section, optimization of the quasi-optical design is required and a guideline of a strategy is presented. As a result of this process and following the guidelines indicated, modifications of the design (new mirrors positions, rotation axes and/or focal properties) will be proposed for the next step of an iterative process, including the mandatory compatibility check with the mechanical constraints.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Matrix phased array (MPA) imaging technology for resistance spot welds

A three-dimensional MPA probe has been incorporated with a high speed phased array electronic board to visualize nugget images of resistance spot welds. The primary application area of this battery operated portable MPA ultrasonic imaging system is in the automotive industry which a conventional destructive testing process is commonly adopted to check the quality of resistance spot welds in auto bodies. Considering an average of five-thousand spot welds in a medium size passenger vehicle, the amount of time and effort given to popping the welds and measuring nugget size are immeasurable in addition to the millions of dollars' worth of scrap metals recycled per plant per year. This wasteful labor intensive destructive testing process has become less reliable as auto body sheet metal has transitioned from thick and heavy mild steels to thin and light high strength steels. Consequently, the necessity of developing a non-destructive inspection methodology has become inevitable. In this paper, the fundamental aspects of the current 3-D probe design, data acquisition algorithms, and weld nugget imaging process are discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2014

Magnetic interactions in a quasi-one-dimensional antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}

A theoretical ab-initio investigation of exchange interaction between Cu atoms in an insulating antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}, en = C{sub 2}H{sub 8}N{sub 2}, is reported. While the previous experimental studies described the system's magnetism to be quasi-two-dimensional, our results, based on a mapping of the system onto an effective Heisenberg model, rather support a quasi-one-dimensional character with the exchange coupling between the Cu atoms being propagated mainly along a zigzag line lying in the crystal's bc plane and connecting the Cu atoms through the N atoms. Further, the direction of magnetic moments on the Cu atoms is suggested to be nearly along the crystal's a axis. A check of the change in the exchange constants induced either by external pressure or by various values of U in the GGA + U approximation is made. Finally, based on experimental values of positions of broad maxima in magnetic-susceptibility and specific-heat curves and using theoretical expressions available in the literature a relevant value of the U parameter and related expected value of the electronic gap are estimated to be about 5 eV and 2 eV, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Zakharov-Kuznetsov equation in a magnetized plasma with two temperature superthermal electrons

A nonlinear Zakharov-Kuznetsov (ZK) equation for ion-acoustic solitary waves (IASWs) in a magnetized plasmas containing kappa distributed cold and hot electrons is derived by using reductive perturbation method. From the solution of ZK equation, the characteristics of IASWs have been studied under the influence of various plasma parameters. Existence domain of physical parameters is determined. It has been observed that the present plasma system supports the existence of both positive as well as negative potential solitons. The combined effects of cold to hot electron temperature ratio (σ), density ratio of cold electrons to ions (f), superthermality of cold and hot electrons (κ{sub c},κ{sub h}), strength of magnetic field (via Ω{sub i}), and obliqueness (θ) significantly influence the profile of IASWs. The physical parameters play a great role to modify the width and amplitude of the solitary structures. The stability analysis is also presented in this investigation and parametric range is determined to check the presence of stable and unstable solitons. The findings of this study are important to the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature electrons with kappa distribution exist.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Wave–vortex interactions in the nonlinear Schrödinger equation

This is a theoretical study of wave–vortex interaction effects in the two-dimensional nonlinear Schrödinger equation, which is a useful conceptual model for the limiting dynamics of superfluid quantum condensates at zero temperature. The particular wave–vortex interaction effects are associated with the scattering and refraction of small-scale linear waves by the straining flows induced by quantized point vortices and, crucially, with the concomitant nonlinear back-reaction, the remote recoil, that these scattered waves exert on the vortices. Our detailed model is a narrow, slowly varying wavetrain of small-amplitude waves refracted by one or two vortices. Weak interactions are studied using a suitable perturbation method in which the nonlinear recoil force on the vortex then arises at second order in wave amplitude, and is computed in terms of a Magnus-type force expression for both finite and infinite wavetrains. In the case of an infinite wavetrain, an explicit asymptotic formula for the scattering angle is also derived and cross-checked against numerical ray tracing. Finally, under suitable conditions a wavetrain can be so strongly refracted that it collapses all the way onto a zero-size point vortex. This is a strong wave–vortex interaction by definition. The conditions for such a collapse are derived and the validity of ray tracing theory during the singular collapse is investigated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Superposition of elliptic functions as solutions for a large number of nonlinear equations

For a large number of nonlinear equations, both discrete and continuum, we demonstrate a kind of linear superposition. We show that whenever a nonlinear equation admits solutions in terms of both Jacobi elliptic functions cn(x, m) and dn(x, m) with modulus m, then it also admits solutions in terms of their sum as well as difference. We have checked this in the case of several nonlinear equations such as the nonlinear Schrödinger equation, MKdV, a mixed KdV-MKdV system, a mixed quadratic-cubic nonlinear Schrödinger equation, the Ablowitz-Ladik equation, the saturable nonlinear Schrödinger equation, λϕ{sup 4}, the discrete MKdV as well as for several coupled field equations. Further, for a large number of nonlinear equations, we show that whenever a nonlinear equation admits a periodic solution in terms of dn{sup 2}(x, m), it also admits solutions in terms of dn {sup 2}(x,m)±√(m) cn (x,m) dn (x,m), even though cn(x, m)dn(x, m) is not a solution of these nonlinear equations. Finally, we also obtain superposed solutions of various forms for several coupled nonlinear equations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Structural and optical characterization of Cr{sub 2}O{sub 3} nanostructures: Evaluation of its dielectric properties

The structural, optical and dielectric properties of as-grown Cr{sub 2}O{sub 3} nanostructures are demonstrated in this paper. Powder X-ray diffractometry analysis confirmed the rhombohedral structure of the material with lattice parameter, a = b = 4.953 Å; c = 13.578 Å, and average crystallize size (62.40 ± 21.3) nm. FE-SEM image illustrated the mixture of different shapes (disk, particle and rod) of as-grown nanostructures whereas; EDS spectrum confirmed the elemental purity of the material. FTIR spectroscopy, revealed the characteristic peaks of Cr–O bond stretching vibrations. Energy band gap (3.2 eV) of the nanostructures has been determined using the results of UV-VIS-NIR spectrophotometer. The dielectric properties of the material were checked in the wide frequency region (100Hz-30 MHz). In the low frequency region, the matrix of the dielectric behaves like source as well as sink of electrical energy within the relaxation time. Low value of dielectric loss exhibits that the materials posses good optical quality with lesser defects. The ac conductivity of the material in the high frequency region was found according to frequency power law. The physical-mechanism and the theoretical-interpretation of dielectric-properties of Cr{sub 2}O{sub 3} nanostructures attest the potential candidature of the material as an efficient dielectric medium.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Calculation of excitation energies from the CC2 linear response theory using Cholesky decomposition

A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model is reported. It employs a Cholesky decomposition of the two-electron integrals that significantly reduces the computational cost and the storage requirements of the method compared to standard implementations. Our algorithm also exploits a partitioning form of the CC2 equations which reduces the dimension of the problem and avoids the storage of doubles amplitudes. We present calculation of excitation energies of benzene using a hierarchy of basis sets and compare the results with conventional CC2 calculations. The reduction of the scaling is evaluated as well as the effect of the Cholesky decomposition parameter on the quality of the results. The new algorithm is used to perform an extrapolation to complete basis set investigation on the spectroscopically interesting benzylallene conformers. A set of calculations on medium-sized molecules is carried out to check the dependence of the accuracy of the results on the decomposition thresholds. Moreover, CC2 singlet excitation energies of the free base porphin are also presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗