bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation between three-dimensional current distribution profiles and surface scatterings in nanostructured materials
Authors: Yang Jack , Li Sean
Published: October 2010

Intensive heat generation associated with surface scattering is a major obstacle for minimizing high performance electronic circuit components beyond submicron scale, a regime in which the device length scale is comparable to the electron inelastic scattering mean free path. In this work, the fundamental physics of surface scattering during the electrical transport process is addressed by quantum mechanical modeling of the current distribution profile in a three-dimensional conduction channel. The results show that the surface potentials act as local scatters that deflect the current from the topmost surface layer, leading to an accumulation of the current density in the subsurface layer. The possible size dependency in such a current distribution profile is proposed based on the scaling theory in weak localization regime. It suggests that for Gaussian-like surface potential profile, the inelastic scattering mean free path decreases as the full width half maximum of the potential profile increases. Surface scatterings are also likely to play an important role in producing the resistivity of extremely narrow conducting channels.
Characteristics of Pt/BiFeO3/TiO2/Si capacitors with TiO2 layer formed by liquid-delivery metal organic chemical vapor deposition
Authors: Xie Dan , Han Xueguang , Li Rui , Ren Tianling , Liu Litian , Zhao Yonggang
Published: October 2010

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 250 nm thick BiFeO3 (BFO) ferroelectric film and 150 nm thick TiO2 layer on silicon substrate have been fabricated and characterized. TiO2 was deposited on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electrical properties of the Pt/BFO/TiO2/Si capacitors were studied. TiO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 3.51 V. When sweeping voltages decreased from ±14 to ±6 V, the memory window width decreased from 3.51 to 1.11 V. The leakage current of the film was of the order of 10−8 A/cm2 at an applied voltage of 4 V.
Comparative study between the reflective optics and lens based system for microwave imaging system on KSTAR
Authors: Lee W. , Yun G. S. , Nam Y. , Hong I. , Kim J. B. , Park H. K. , Tobias B. , Liang T. , Domier C. W. , Luhmann N. C.
Published: October 2010

Recently, two-dimensional microwave imaging diagnostics such as the electron cyclotron emission imaging (ECEI) system and microwave imaging reflectometry (MIR) have been developed to study magnetohydrodynamics instabilities and turbulence in magnetically confined plasmas. These imaging systems utilize large optics to collect passive emission or reflected radiation. The design of this optics can be classified into two different types: reflective or refractive optical systems. For instance, an ECEI/MIR system on the TEXTOR tokamak [Park et al., Rev. Sci. Instrum. 75, 3787 (2004)] employed the reflective optics which consisted of two large mirrors, while the TEXTOR ECEI upgrade [B. Tobias et al., Rev. Sci. Instrum. 80, 093502 (2009)] and systems on DIII-D, ASDEX-U, and KSTAR adopted refractive systems. Each system has advantages and disadvantages in the standing wave problem and optical aberrations. In this paper, a comparative study between the two optical systems has been performed in order to design a MIR system for KSTAR.
Radiation hardening of gated x-ray imagers for the National Ignition Facility (invited)
Authors: Bell P. M. , Bradley D. K. , Kilkenny J. D. , Conder A. , Cerjan C. , Hagmann C. , Hey D. , Izumi N. , Moody J. , Teruya A. , Celeste J. , Kimbrough J. , Khater H. , Eckart M. J. , Ayers J.
Published: October 2010

The National Ignition Facility will soon be producing x-ray flux and neutron yields higher than any produced in laser driven implosion experiments in the past. Even a non-igniting capsule will require x-ray imaging of near burning plasmas at 1017 neutrons, requiring x-ray recording systems to work in more hostile conditions than we have encountered in past laser facilities. We will present modeling, experimental data and design concepts for x-ray imaging with electronic recording systems for this environment (ARIANE). A novel instrument, active readout in a nuclear environment, is described which uses the time-of-flight difference between the gated x-ray signal and the neutron which induces a background signal to increase the yield at which gated cameras can be used.
Images of the laser entrance hole from the static x-ray imager at NIF
Authors: Schneider M. B. , Jones O. S. , Meezan N. B. , Milovich J. L. , Town R. P. , Alvarez S. S. , Beeler R. G. , Bradley D. K. , Celeste J. R. , Dixit S. N. , Edwards M. J. , Haugh M. J. , Kalantar D. H. , Kline J. L. , Kyrala G. A. , Landen O. L. , MacGowan B. J. , Michel P. , Moody J. D. , Oberhelman S. K. , Piston K. W. , Pivovaroff M. J. , Suter L. J. , Teruya A. T. , Thomas C. A. , Vernon S. P. , Warrick A. L. , Widmann K. , Wood R. D. , Young B. K.
Published: October 2010

The static x-ray imager at the National Ignition Facility is a pinhole camera using a CCD detector to obtain images of Hohlraum wall x-ray drive illumination patterns seen through the laser entrance hole (LEH). Carefully chosen filters, combined with the CCD response, allow recording images in the x-ray range of 3–5 keV with 60 μm spatial resolution. The routines used to obtain the apparent size of the backlit LEH and the location and intensity of beam spots are discussed and compared to predictions. A new soft x-ray channel centered at 870 eV (near the x-ray peak of a 300 eV temperature ignition Hohlraum) is discussed.
Coherent Rayleigh–Brillouin scattering measurements of bulk viscosity of polar and nonpolar gases, and kinetic theory
Authors: Meijer A. S. , de Wijn A. S. , Peters M. F. E. , Dam N. J. , van de Water W.
Published: October 2010

We investigate coherent Rayleigh–Brillouin spectroscopy as an efficient process to measure the bulk viscosity of gases at gigahertz frequencies. Scattered spectral distributions are measured using a Fizeau spectrometer. We discuss the statistical error due to the fluctuating mode structure of the used pump laser. Experiments were done for both polar and nonpolar gases and the bulk viscosity was obtained from the spectra using the Tenti S6 model. Results are compared to simple classical kinetic models of molecules with internal degrees of freedom. At the extremely high (gigahertz) frequencies of our experiment, most internal vibrational modes remain frozen and the bulk viscosity is dominated by the rotational degrees of freedom. Our measurements show that the molecular dipole moments have unexpectedly little influence on the bulk viscosity at room temperature and moderate pressure.
Microfluidic force spectroscopy for characterization of biomolecular interactions with piconewton resolution
Authors: Javanmard M. , Babrzadeh F. , Davis R. W.
Published: October 2010

In this paper we present a scalable method based on the use of microfluidics and shear force spectroscopy which can be used for determining the affinity between molecules. Our method involves the use of functionalization of the surface of microfluidic channels with ligand molecules, and the surface of microspheres with receptor molecules. Bound beads are detached from the surface of the microchannels using pressure driven flow. The drag force required to detach the beads is used to determine the affinity of the bond holding the two molecules together. The minimum force we are able to detect is 5 pN. We have used this method to determine the binding force between protein-protein interactions and DNA base-pair interactions. We also have shown the ability of this technique to distinguish between strong and weak protein-protein interactions. Using this approach, it may be possible to multiplex an array of these functionalized channels onto a chip and probe the interactions between large varieties of biomolecules.
Microsecond time-resolved Fourier transform infrared analytics in a low pressure glow discharge reactor
Authors: Rivallan Mickaël , Aiello Sébastien , Thibault-Starzyk Frédéric
Published: October 2010

A low pressure glow discharge reactor has been designed to allow time-resolved infrared spectroscopic investigation of the discharge zone in practical conditions. The benefits of such reactor are demonstrated through the study of the evolution in the infrared spectra of air/CO2 gas mixture at the microsecond time-scale. It has been shown that the spectra are greatly affected by the electrical discharge in the 2400–2200 cm−1 region, where the asymmetric stretch mode of CO2 falls. The CO2 molecules are excited through a collision with excited N2 molecules, where the transfer of energy occurs by a resonant effect. The mechanisms involved are reversible and following plasma pulses.
The National Ignition Facility neutron time-of-flight system and its initial performance (invited)
Authors: Glebov V. Yu. , Sangster T. C. , Stoeckl C. , Knauer J. P. , Theobald W. , Marshall K. L. , Shoup M. J. , Buczek T. , Cruz M. , Duffy T. , Romanofsky M. , Fox M. , Pruyne A. , Moran M. J. , Lerche R. A. , McNaney J. , Kilkenny J. D. , Eckart M. J. , Schneider D. , Munro D. , Stoeffl W. , Zacharias R. , Haslam J. J. , Clancy T. , Yeoman M. , Warwas D. , Horsfield C. J. , Bourgade J.-L. , Landoas O. , Disdier L. , Chandler G. A. , Leeper R. J.
Published: October 2010

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D2) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 108 to 1019), neutron bang time in DT implosions between 1012 and 1016, and to infer areal density for DT yields above 1012. During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D2 fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.
Direct detection of lower hybrid wave using a reflectometer on Alcator C-Mod
Authors: Shiraiwa S. , Baek S. , Dominguez A. , Marmar E. , Parker R. , Kramer G. J.
Published: October 2010

The possibility of directly detecting a density perturbation produced by lower hybrid (LH) waves using a reflectometer is presented. We investigate the microwave scattering of reflectometer probe beams by a model density fluctuation produced by short wavelength LH waves in an Alcator C-Mod experimental condition. In the O-mode case, the maximum response of phase measurement is found to occur when the density perturbation is approximately centimeters in front of the antenna, where Bragg scattering condition is satisfied. In the X-mode case, the phase measurement is predicted to be more sensitive to the density fluctuation close to the cut-off layer. A feasibility test was carried out using a 50 GHz O-mode reflectometer on the Alcator C-Mod tokamak, and positive results including the detection of 4.6 GHz pump wave and parametric decay instabilities were obtained.
Fringe-jump corrected far infrared tangential interferometer/polarimeter for a real-time density feedback control system of NSTX plasmas
Authors: Juhn J.-W. , Lee K. C. , Hwang Y. S. , Domier C. W. , Luhmann N. C. , Leblanc B. P. , Mueller D. , Gates D. A. , Kaita R.
Published: October 2010

The far infrared tangential interferometer/polarimeter (FIReTIP) of the National Spherical Torus Experiment (NSTX) has been set up to provide reliable electron density signals for a real-time density feedback control system. This work consists of two main parts: suppression of the fringe jumps that have been prohibiting the plasma density from use in the direct feedback to actuators and the conceptual design of a density feedback control system including the FIReTIP, control hardware, and software that takes advantage of the NSTX plasma control system (PCS). By investigating numerous shot data after July 2009 when the new electronics were installed, fringe jumps in the FIReTIP are well characterized, and consequently the suppressing algorithms are working properly as shown in comparisons with the Thomson scattering diagnostic. This approach is also applicable to signals taken at a 5 kHz sampling rate, which is a fundamental constraint imposed by the digitizers providing inputs to the PCS. The fringe jump correction algorithm, as well as safety and feedback modules, will be included as submodules either in the gas injection system category or a new category of density in the PCS.
Electromagnetic power loss in open coaxial diodes and the Langmuir–Blodgett law
Authors: Kumar Raghwendra , Biswas Debabrata
Published: October 2010

The space charge limited current in coaxial diodes with electromagnetic power loss is studied. The Langmuir–Blodgett law is expressed in terms of the electromagnetic power loss and the applied voltage. Particle-in-cell simulations of photodiode-like situations and high power diodes confirm the relation between the applied voltage, diode voltage, and electromagnetic power loss.
Femtosecond midinfrared study of aggregation behavior in aqueous solutions of amphiphilic molecules
Authors: Petersen Christian , Bakulin Artem A. , Pavelyev Vlad G. , Pshenichnikov Maxim S. , Bakker Huib J.
Published: October 2010

We study the spectral and orientational dynamics of HDO molecules in aqueous solutions of different concentrations of tertiary butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO). The spectral dynamics is investigated with femtosecond two-dimensional infrared spectroscopy of the O–H stretch vibration of HDO:D2O, and the orientational dynamics is studied with femtosecond polarization-resolved pump-probe spectroscopy of the O–D stretch vibration of HDO:H2O. Both the spectral and orientational dynamics are observed to show bimodal behavior: part of the water molecules shows spectral and orientational dynamics similar to bulk liquid water and part of the water molecules displays a much slower dynamics. For low solute concentrations, the latter fraction of slow water increases linearly as a function of solute molality, indicating that the slow water is contained in the solvation shells of TBA and TMAO. At higher concentrations, the fraction of slow water saturates. The saturation behavior is much stronger for TBA solutions than for TMAO solutions, indicating the aggregation of the TBA molecules.
On the effects of liquid-gas interfacial shear on slip flow through a parallel-plate channel with superhydrophobic grooved walls
Authors: Ng Chiu-On , Chu Henry C. W. , Wang C. Y.
Published: October 2010

Comparisons between slip lengths predicted by a liquid-gas coupled model and that by an idealized zero-gas-shear model are presented in this paper. The problem under consideration is pressure-driven flow of a liquid through a plane channel bounded by two superhydrophobic walls which are patterned with longitudinal or transverse gas-filled grooves. Effective slip arises from lubrication on the liquid-gas interface and intrinsic slippage on the solid phase of the wall. In the mathematical models, the velocities are analytically expressed in terms of eigenfunction series expansions, where the unknown coefficients are determined by the matching of velocities and shear stresses on the liquid-gas interface. Results are generated to show the effects due to small but finite gas viscosity on the effective slip lengths as functions of the channel height, the depth of grooves, the gas area fraction of the wall, and intrinsic slippage of the solid phase. Conditions under which even a gas/liquid viscosity ratio as small as 0.01 may have appreciable effects on the slip lengths are discussed.
Experimental verification of metamaterial based subwavelength microwave absorbers
Authors: Alici Kamil Boratay , Bilotti Filiberto , Vegni Lucio , Ozbay Ekmel
Published: October 2010

We designed, implemented, and experimentally characterized electrically thin microwave absorbers by using the metamaterial concept. The absorbers consist of (i) a metal back plate and an artificial magnetic material layer; (ii) metamaterial back plate and a resistive sheet layer. We investigated absorber performance in terms of absorbance, fractional bandwidth, and electrical thickness, all of which depend on the dimensions of the metamaterial unit cell and the distance between the back plate and metamaterial layer. As a proof of concept, we demonstrated a λ/4.7 thick absorber of type I, with a 99.8% absorption peak along with a 8% fractional bandwidth. We have shown that as the electrical size of the metamaterial unit cell decreases, the absorber electrical thickness can further be reduced. We investigated this concept by using two different magnetic metamaterial inclusions: the split-ring resonator (SRR) and multiple SSR (MSRR). We have also demonstrated experimentally a λ/4.7 and a λ/4.2 thick absorbers of type II, based on SRR and MSRR magnetic metamaterial back plates, respectively. The absorption peak of the SRR layout is 97.4%, while for the MSRR one the absorption peak is 98.4%. The 10 dB bandwidths were 9.9% and 9.6% for the SRR and MSRR cases, respectively.
Nonideal parasitic resistance effects in bulk heterojunction organic solar cells
Authors: Tumbleston John R. , Ko Doo-Hyun , Samulski Edward T. , Lopez Rene
Published: October 2010

A common assumption in both experimental measurements and device modeling of bulk heterojunction (BHJ) organic solar cells is that parasitic resistances are ideal. In other words, series resistance (Rsr) is near zero while shunt resistance (Rsh) approaches infinity. Relaxation of this assumption affects device performance differently depending on the chosen BHJ material system. Specifically, the impact of nonideal Rsr is controlled by the electric field dependence of the probability of charge transfer (CT) state dissociation (PCT). This is demonstrated by evaluating the experimental current density versus voltage response within the framework of a drift/diffusion model for two BHJ systems that strongly differ in PCT. Second, light intensity measurements of devices with nonideal Rsr and Rsh are shown to convolute the scaling of short-circuit current and open-circuit voltage with light intensity, which is a common technique to study BHJ device physics. Finally, we show the connection between the drift/diffusion and equivalent circuit model with regard to each model’s treatment of CT state dissociation. In particular, the equivalent circuit model utilizes a light intensity dependent Rsh to describe this dissociation process and predicts a photocurrent under reverse bias that exceeds the photocurrent permitted by light absorption.
Signatures of d-wave symmetry on thermal Dirac fermions in graphene-based F|I|d junctions
Authors: Salehi Morteza , Alidoust Mohammad , Rashedi Gholamreza
Published: October 2010

We study theoretically behavior of thermal massless Dirac fermions inside graphene-based Ferromagnetic |Insulator| d-wave/s-wave superconductor (F|I|d and F|I|S) junctions in the ballistic regime. We employ Dirac–Bogoliubov–de Genne formalism and use Dirac–BdG wave functions within the ferromagnetic, normal, and superconducting regions and appropriate boundary conditions, to derive Andreev and normal reflection coefficients. By employing the obtained Andreev and normal reflection coefficients, thin barrier approximation and also appropriate values of parameters, we investigate characteristics of heat current through the F|I|d and F|I|S junctions. We find that for s-wave superconductors, thermal conductance (Γ) oscillates sinusoidally versus strength of barrier in the thin barrier approximation. The finding persists for all values of α, orientation of d-wave superconductor crystal in the k-space, for values of α very close to π/4, magnitude of the oscillations suppress completely. By increasing temperature, the thermal conductance increases exponentially for small values of α and for larger values of superconductor crystal orientation angle the thermal conductance modifies and interestingly for α=π/4 exhibits linear behavior, i.e., Γ∝T which is similar to Wiedemann–Franz law for metals in low temperatures. While increasing the temperature move minimum value of the thermal conductance with respect to strength of magnetization texture h/Δ0 towards smaller values of h/Δ0, increasing the superconductor crystal orientation angle, α from 0 to π/4 enhances whole values of the thermal conductance and consequently the minimum value move towards up. At last we suggest an experimental setup for verifying these findings.
Overloading effect of energetic electrons in the bubble regime of laser wakefield acceleration
Authors: Xu Jiancai , Shen Baifei , Zhang Xiaomei , Wen Meng , Ji Liangliang , Wang Wenpeng , Yu Yahong , Li Yuelin
Published: October 2010

The overloading effect of self-injected high-charge electron bunch in the bubble regime of laser wakefield acceleration is studied. When too many electrons are trapped by the bubble, the wakefield can be strongly modified, preventing further injection of the background electrons. This process is directly observed in two-dimensional particle-in-cell simulation and is explained using a one-dimensional wake model. For obtaining significantly more energetic electrons, the use of a decreasing plasma density profile is proposed.
The MAST motional Stark effect diagnostic
Authors: Conway N. J. , De Bock M. F. M. , Michael C. A. , Walsh M. J. , Carolan P. G. , Hawkes N. C. , Rachlew E. , McCone J. F. G. , Shibaev S. , Wearing G.
Published: October 2010

A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of ∼2.5 cm, and time resolution of ∼1 ms at angular noise levels of ∼0.5°. Conventional (albeit very narrow) interference filters isolate π or σ polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The π component is observed to be significantly stronger than σ, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on π. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses.
Design of collection optics and polychromators for a JT-60SA Thomson scattering system
Authors: Tojo H. , Hatae T. , Sakuma T. , Hamano T. , Itami K. , Aida Y. , Suitoh S. , Fujie D.
Published: October 2010

This paper presents designs of collection optics for a JT-60SA Thomson scattering system. By using tangential (to the toroidal direction) YAG laser injection, three collection optics without strong chromatic aberration generated by the wide viewing angle and small design volume were found to measure almost all the radial space. For edge plasma measurements, the authors optimized the channel number and wavelength ranges of band-pass filters in a polychromator to reduce the relative error in Te by considering all spatial channels and a double-pass laser system with different geometric parameters.
A general assessment method for subgrid-scale models in large-eddy simulation
Authors: Cassart B. , Teaca B. , Carati D.
Published: October 2010

A method combining the advantages of a priori and a posteriori testing approaches for subgrid-scale models in large-eddy simulation (LES) is proposed. It is implemented with various simple eddy viscosity models for decaying homogeneous turbulence. The method relies on the introduction of a restoring force in addition to the subgrid model. This force maintains the LES velocity field in the vicinity of the filtered velocity obtained from an accurately simulated flow. The analysis of this force provides new diagnostics on the efficiency of the subgrid-scale models.
Design and measurement of a Cu L-edge x-ray filter for free electron laser pumped x-ray laser experiments
Authors: Dunn J. , London R. A. , Cone K. V. , Rocca J. J. , Rohringer N.
Published: October 2010

An inner-shell photoionized x-ray laser pumped by the Linac Coherent Light Source (LCLS) free electron laser has been proposed recently. The measurement of the on-axis 849 eV Ne Kα laser and protection of the x-ray spectrometer from damage require attenuation of the 1 keV LCLS beam. An Al/Cu foil combination is well suited, serving as a low energy bandpass filter below the Cu L-edge at 933 eV. A high resolution grating spectrometer is used to measure the transmission of a candidate filter with an intense laser-produced x-ray backlighter developed at the Lawrence Livermore National Laboratory Jupiter Laser Facility Janus. The methodology and discussion of the observed fine structure above the Cu L-edge will be presented.
Quantitative studies on inner interfaces in conical metal joints using hard x-ray inline phase contrast radiography
Authors: Zabler S. , Rack T. , Rack A. , Nelson K.
Published: October 2010

Quantitative investigation of micrometer and submicrometer gaps between joining metal surfaces is applied to conical plug-socket connections in dental titanium implants. Microgaps of widths well beyond the resolving power of industrial x-ray systems are imaged by synchrotron phase contrast radiography. Furthermore, by using an analytical model for the relatively simple sample geometry and applying it to numerical forward simulations of the optical Fresnel propagation, we show that quantitative measurements of the microgap width down to 0.1 μm are possible. Image data recorded at the BAMline (BESSY-II light source, Germany) are presented, with the resolving power of the imaging system being 4 μm in absorption mode and ∼14 μm in phase contrast mode (z2=0.74 m). Thus, phase contrast radiography, combined with numerical forward simulations, is capable of measuring the widths of gaps that are two orders of magnitude thinner than the conventional detection limit.
Particle-in-cell simulation of hydrogen discharge driven by combined radio frequency and pulse sources
Authors: Sun Jizhong , Li Xiantao , Sang Chaofeng , Jiang Wei , Zhang Pengyun , Wang Dezhen
Published: October 2010

A particle-in-cell plus Monte Carlo collision model is employed to investigate the low pressure hydrogen capacitive discharge driven by combined radio frequency (rf) and pulse sources. This work focuses on the evolutions of electron energy and density in the discharge to illustrate the role that a short pulse source plays. The simulation results show that an extra short pulse source can modulate the electron energy effectively: in the early and late pulse-on times, the electron energy is much higher than that in the single rf source discharge; during the pulse-off time, the electron energy can drop gradually to a low value. It is also found that a few peaks of attenuated electron energy appear periodically just after the pulse voltage drops to zero. The similar phenomena can also be found in the production rate of highly vibrationally excited hydrogen molecules. Physical mechanisms responsible for these phenomena are discussed.
Enhancement of cross-field transport into the private region of detached-divertor in Large Helical Device
Authors: Tanaka H. , Ohno N. , Tsuji Y. , Kajita S. , Masuzaki S. , Kobayashi M. , Morisaki T. , Tsuchiya H. , Komori A. ,   the LHD Experimental Group
Published: October 2010

The fluctuation of ion saturation currents in the attached- and detached-divertor plasmas of the Large Helical Device [Fujiwara et al., Nucl. Fusion 41, 1355 (2001)] has been measured using a Langmuir probe array embedded in a divertor plate. Analytical results indicate that these fluctuation properties differ considerably from each other; for instance, the mean value distribution expands to and positive spikes propagate toward a private region from the divertor leg in the detached-divertor. We investigated the magnetic field lines traced from probe electrodes by using the KMAG code [Nakamura et al., J. Plasma Fusion Res. 69, 41 (1993)], and it is then confirmed that the propagation direction of positive spikes corresponds to that predicted by the theory of blobby plasma transport. This phenomenon is expected to lead to the broadening of plasma particle and heat fluxes to the divertor plate.
Gas flow effects on the submicrosecond pulsed atmospheric pressure glow discharges
Authors: Liu Fucheng , Zhang Dingzong , Wang Dezhen
Published: October 2010

The influence of gas flow on the discharge characteristics in the submicrosecond pulsed dielectric barrier discharge at atmospheric pressure was investigated by a one-dimensional self-consistent kinetic model. The convection-transport mechanism of the plasma species caused by a longitudinal gas flow was integrated into flux equation. Two discharge current pulses, the positive one and the negative one, are operated in a normal glow mode and a subnormal glow mode, respectively. It is shown that the gas flow has a significant impact on the discharge characteristics, especially on the positive discharge pulse. The spatial distribution of electrons is affected by the gas flow through the convection transport mechanism.
A framework and methodology for reporting geographically and temporally resolved solar data: A case study of Texas
Authors: Wogan David M. , Webber Michael , da Silva Alexandre K.
Published: October 2010

This paper presents a framework and methodology for reporting measured solar radiation data. Geographically and temporally resolved solar data have been calculated for all 254 counties in Texas using geospatial interpolation of data from 24 existing terrestrial measurement locations. Hourly global, direct, and diffuse horizontal radiation data have been obtained from 15 measurement sites at the Texas Solar Radiation Database, a project at The University of Texas at Austin, and from 9 sites at the National Solar Radiation Database. Average radiation fluxes and peak insolation have been calculated using daylight hours in addition to the total energy in kWh∕m2day. The methodology presented in this paper provides solar insolation data in a convenient format for engineers, scientists, policy-makers, homeowners, and consumers to assess the potential of solar energy at the county resolution. This methodology enables informed decisions about the economic viability of solar installations at particular locations and with useful diurnal and seasonal fidelity. These results are presented in a series of maps, figures, and tables included in this paper.
Interpolation between Airy and Poisson statistics for unitary chiral non-Hermitian random matrix ensembles
Authors: Akemann G. , Bender M.
Published: October 2010

We consider a family of chiral non-Hermitian Gaussian random matrices in the unitarily invariant symmetry class. The eigenvalue distribution in this model is expressed in terms of Laguerre polynomials in the complex plane. These are orthogonal with respect to a non-Gaussian weight including a modified Bessel function of the second kind, and we give an elementary proof for this. In the large n limit, the eigenvalue statistics at the spectral edge close to the real axis are described by the same family of kernels interpolating between Airy and Poisson that was recently found by one of the authors for the elliptic Ginibre ensemble. We conclude that this scaling limit is universal, appearing for two different non-Hermitian random matrix ensembles with unitary symmetry. As a second result we give an equivalent form for the interpolating Airy kernel in terms of a single real integral, similar to representations for the asymptotic kernel in the bulk and at the hard edge of the spectrum. This makes its structure as a one-parameter deformation of the Airy kernel more transparent.
GEANT4 simulations of Cherenkov reaction history diagnostics
Authors: Rubery M. S. , Horsfield C. J. , Herrmann H. W. , Kim Y. , Mack J. M. , Young C. S. , Caldwell S. E. , Evans S. C. , Sedilleo T. J. , McEvoy A. , Miller E. K. , Stoeffl W. , Ali Z. , Toebbe J.
Published: October 2010

This paper compares the results from a GEANT4 simulation of the gas Cherenkov detector 1 (GCD1) with previous simulations and experimental data from the Omega laser facility. The GCD1 collects gammas emitted during a deuterium-tritium capsule implosion and converts them, through several processes, to Cherenkov light. Photon signals are recorded using subnanosecond photomultiplier tubes, producing burn reaction histories. The GEANT4 GCD1 simulation is first benchmarked against ACCEPT, an integrated tiger series code, with good agreement. The simulation is subsequently compared with data from the Omega laser facility, where experiments have been performed to measure the effects of Hohlraum materials on reaction history signals, in preparation for experiments at the National Ignition Facility.
Multichannel Langmuir probe for turbulence study in Heliotron J
Authors: Ohshima S. , Yamamoto S. , Takeuchi M. , Nagasaki K. , Mizuuchi T. , Okada H. , Minami T. , Kobayashi S. , Hanatani K. , Konoshima S. , Sano F.
Published: October 2010

New multichannel Langmuir probe system was developed and installed to Heliotron J. The objective of the new probe is to characterize basic turbulence property and the resulting transport in advanced helical configuration. The probe developed here consists of four sets of triple probe and one pin for floating potential measurement. Initial experiments in neutral beam heating plasma were conducted and fluctuation profile of radial and poloidal electric fields and Reynolds stress were estimated. For precise evaluation of the electric fields and Reynolds stress, a technique to compensate radial change of tilt angle between probe array and magnetic surface was proposed and applied to the initial results obtained in edge region of Heliotron J where the complicated magnetic structure exists.
Modeling the National Ignition Facility neutron imaging system
Authors: Wilson D. C. , Grim G. P. , Tregillis I. L. , Wilke M. D. , Patel M. V. , Sepke S. M. , Morgan G. L. , Hatarik R. , Loomis E. N. , Wilde C. H. , Oertel J. A. , Fatherley V. E. , Clark D. D. , Fittinghoff D. N. , Bower D. E. , Schmitt M. J. , Marinak M. M. , Munro D. H. , Merrill F. E. , Moran M. J. , Wang T.-S. F. , Danly C. R. , Hilko R. A. , Batha S. H. , Frank M. , Buckles R.
Published: October 2010

Numerical modeling of the neutron imaging system for the National Ignition Facility (NIF), forward from calculated target neutron emission to a camera image, will guide both the reduction of data and the future development of the system. Located 28 m from target chamber center, the system can produce two images at different neutron energies by gating on neutron arrival time. The brighter image, using neutrons near 14 MeV, reflects the size and symmetry of the implosion “hot spot.” A second image in scattered neutrons, 10–12 MeV, reflects the size and symmetry of colder, denser fuel, but with only ∼1%–7% of the neutrons. A misalignment of the pinhole assembly up to ±175 μm is covered by a set of 37 subapertures with different pointings. The model includes the variability of the pinhole point spread function across the field of view. Omega experiments provided absolute calibration, scintillator spatial broadening, and the level of residual light in the down-scattered image from the primary neutrons. Application of the model to light decay measurements of EJ399, BC422, BCF99-55, Xylene, DPAC-30, and Liquid A suggests that DPAC-30 and Liquid A would be preferred over the BCF99-55 scintillator chosen for the first NIF system, if they could be fabricated into detectors with sufficient resolution.
Dust ion-acoustic solitary and shock waves due to dust charge fluctuation with vortexlike electrons
Authors: Duha S. S. , Anowar M. G. M. , Mamun A. A.
Published: October 2010

A rigorous theoretical investigation has been made of the dust ion-acoustic (DIA) solitary and shock waves in an unmagnetized dusty plasma (containing vortexlike electrons, mobile ions, and charge fluctuating static dust) by reductive perturbation method. The effects of dust grain charge fluctuation and vortexlike (trapped) electron are found to modify the properties of the DIA solitary and shock waves significantly. The implications of these results for some space and astrophysical dusty plasma systems, especially planetary ring systems, are briefly mentioned.
Theory of unfolded cyclotron accelerator
Authors: Rax J.-M. , Robiche J.
Published: October 2010

An acceleration process based on the interaction between an ion, a tapered periodic magnetic structure, and a circularly polarized oscillating electric field is identified and analyzed, and its potential is evaluated. A Hamiltonian analysis is developed in order to describe the interplay between the cyclotron motion, the electric acceleration, and the magnetic modulation. The parameters of this universal class of magnetic modulation leading to continuous acceleration without Larmor radius increase are expressed analytically. Thus, this study provides the basic scaling of what appears as a compact unfolded cyclotron accelerator.
Generation of high charged energetic electrons by using multiparallel laser pulses
Authors: Wen Meng , Shen Baifei , Zhang Xiaomei , Ji Liangliang , Wang Wenpeng , Xu Jiancai , Yu Yahong
Published: October 2010

Large amount of energetic electrons generated in laser wake fields driven by multiparallel laser pulses is investigated with three-dimensional particle-in-cell simulations. By adjusting the distance between the pulses, bubbles with different structure are formed, which results in different injection efficiency. Compared with the single-pulse case, the charge of the energetic electrons could be doubled when the distance between the two pulses is large enough. A characteristic distance between the pulses is obtained, above which the total amount of the energetic electrons increases linearly by applying more laser pulses. There is no limit for the charge increase in our scheme as long as the plasma is wide enough so that more pulses can be applied.
Computation of charge and ion drag force on multiple static spherical dust grains immersed in rf discharges
Authors: Ikkurthi V. R. , Matyash K. , Melzer A. , Schneider R.
Published: October 2010

Charging of multiple spherical dust grains located in presheath and sheath regions of an rf discharge has been studied using a three-dimensional particle-particle-particle-mesh (P3M) code. First, dust charge, potential, and ion drag force on two dust particles for various interparticle separations are computed. It is found that for dust separations larger than the shielding length the dust parameters for the two dust particles match with the single particle values. As the dust separation is equal to or less than the shielding length, the transverse component of ion force increases which is due to dynamic shielding effect caused by neighboring dust particle. However, dust charge, potential, and ion drag are found not to be affected considerably. Further, dust charge and potential on an arrangement of nine dust particles are computed. The dust charge and potential do not differ much from the single particle values for the presheath. However the dust charges of multiple dust particles in the sheath are much less negative compared to the single dust case which is shown to be due to ion focusing.
Real-time reflectometry measurement validation in H-mode regimes for plasma position control
Authors: Santos J. , Guimarais L. , Manso M. ,   ASDEX Upgrade Team
Published: October 2010

It has been shown that in H-mode regimes, reflectometry electron density profiles and an estimate for the density at the separatrix can be jointly used to track the separatrix within the precision required for plasma position control on ITER. We present a method to automatically remove, from the position estimation procedure, measurements performed during collapse and recovery phases of edge localized modes (ELMs). Based on the rejection mechanism, the method also produces an estimate confidence value to be fed to the position feedback controller. Preliminary results show that the method improves the real-time experimental separatrix tracking capabilities and has the potential to eliminate the need for an external online source of ELM event signaling during control feedback operation.
Simulation of reflectometry Bragg backscattering spectral responses in the absence of a cutoff layer
Authors: da Silva F. , da Graça S. , Heuraux S. , Conway G. D. ,   ASDEX Upgrade Team
Published: October 2010

Experimental reflectometry signals obtained in the absence of a cutoff layer, with the possibility of interferometric operation excluded, show a coherent and recurrent frequency spectrum signature similar to an Alfvén cascade signature. A possible explanation resides in the modulation of a resonant Bragg backscattering response by an Alfvén mode structure located at the center of the plasma whose frequency of oscillation modulates the backscattered signal in a conformable way. This situation is modeled and simulated using an O-mode full-wave Maxwell finite-difference time-domain code and the resulting signatures are discussed.
Kinetic theory of electromagnetic plane wave obliquely incident on bounded plasma slab
Authors: Angus J. R. , Krasheninnikov S. I. , Smolyakov A. I.
Published: October 2010

The effects of electromagnetic plane waves obliquely incident on a warm bounded plasma slab of finite length L are studied by solving the coupled Vlasov–Maxwell set of equations. It is shown that the solution can be greatly simplified in the limit where thermal effects are most important by expanding in small parameters and introducing self-similar variables. These solutions reveal that the coupling of thermal effects with the angle of incidence is negligible in the region of bounce resonance and anomalous skin effect. In the region of the anomalous skin effect, the heating is shown to scale linearly with the anomalous skin depth δa when δa⪡L, in agreement with previous authors. Furthermore, for δa⪢L, the heating is shown to decay with 1/δa3. The transmission is found to be exponentially larger than that predicted from a local theory in the appropriate region of the anomalous skin effect.
Scattering of radio frequency waves by blob-filaments
Authors: Myra J. R. , D’Ippolito D. A.
Published: October 2010

Radio frequency waves used for heating and current drive in magnetic confinement experiments must traverse the scrape-off-layer (SOL) and edge plasma before reaching the core. The edge and SOL plasmas are strongly turbulent and intermittent in both space and time. As a first approximation, the SOL can be treated as a tenuous background plasma upon which denser filamentary field-aligned blobs of plasma are superimposed. The blobs are approximately stationary on the rf time scale. The scattering of plane waves in the ion-cyclotron to lower-hybrid frequency range from a cylindrical blob is treated here in the cold plasma fluid model. Scattering widths are derived for incident fast and slow waves, and the scattered power fraction is estimated. Processes such as scattering-induced mode conversion, scattering resonances, and shadowing are investigated.
Ion acceleration enhanced by additional neutralizing electrons in a magnetically expanding double layer plasma
Authors: Takahashi Kazunori , Fujiwara Tamiya
Published: October 2010

Electrons neutralizing an ion beam are additionally supplied to a magnetically expanding double layer (DL) plasma from the downstream side of the DL. The rf power and the argon gas pressure are maintained at 200 W and 55 mPa, respectively, and the source magnetic field is varied in the range of about 70–550 G. It is observed that the ion beam energy corresponding to the DL potential drop increases up to 30 eV with an increase in the magnetic field when supplying the additional electrons, while it saturates at 20 eV for the case of the absence of the additional electrons. The supplied electrons are believed to be an energy source for the DL such that increasing the magnetic field is able to increase the potential drop beyond the limit found in the absence of the supplied electrons.
Acoustic confinement and waveguiding with a line-defect structure in phononic crystal slabs
Authors: Khelif Abdelkrim , Mohammadi Saeed , Eftekhar Ali Asghar , Adibi Ali , Aoubiza Boujamaa
Published: October 2010

We present a new way of forming phononic crystal waveguides by coupling a series of line-defect resonators. The dispersion proprieties of these coupled resonator acoustic waveguides (CRAW) can be engineered by using their geometrical parameters. We show that single-mode guiding over a large bandwidth is possible in CRAW formed in a honeycomb-lattice phononic crystal slab of holes in zinc oxide. In addition, a finite length of CRAW structure acts as an efficient selective acoustic filter for Lamb waves.
Effects of particle contamination and substrate interaction on the Raman response of unintentionally doped graphene
Authors: Caridad J. M. , Rossella F. , Bellani V. , Maicas M. , Patrini M. , Díez E.
Published: October 2010

We investigated the inhomogeneities in the charge density of unintentionally doped graphene on SiO2 prepared by mechanical exfoliation. From the analysis of the G, D, and 2D phonon modes of the Raman spectra after displacing contaminants on graphene surface, and measuring the separation monolayer-substrate distance among zones with different doping levels, we deduce that the interaction with the substrate is the main cause of doping in graphene rather than particle contamination. In particular, we show how graphene doping levels vary within the same flake depending on the distance between graphene and the substrate.
High temperature ferromagnetism and optical properties of Co doped ZnO nanoparticles
Authors: Pal Bappaditya , Giri P. K.
Published: October 2010

We report on the occurrence of high temperature ferromagnetism (FM) in ZnO nanoparticles (NPs) doped with Co-atoms. ZnO NPs of two different initial sizes are doped with 3% and 5% Co using ball milling and FM is studied at room temperature and above. X-ray diffraction and high-resolution transmission electron microscopy analysis confirm the absence of metallic Co clusters or any other phase different from würtzite-type ZnO. UV-visible absorption studies show change in band structure and photoluminescence studies show green emission band at 520 nm indicating incorporation of Co-atoms and presence of oxygen vacancy defects, respectively in ZnO lattice. Micro-Raman studies of doped samples shows defect related additional bands at 547 and 574 cm−1. XRD and Raman spectra provide clear evidence for strain in the doped ZnO NPs. The field dependence of magnetization (M-H curve) measured at room temperature exhibits the clear FM with saturation magnetization (Ms) and coercive field (Hc) of the order of 3–7 emu/g and 260 Oe, respectively. Temperature dependence of magnetization (M-T) measurement shows sharp ferromagnetic to paramagnetic transition with a high Curie temperature (Tc) of ∼800 K for 3% Co doped ZnO NPs. It is found that doping at 5% and higher concentration does not exhibit a proper magnetic transition. We attempt to fit the observed FM data with the bound magnetic polaron (BMP) model involving localized carriers and magnetic cations. However, calculated concentration of the BMPs is well below the typical percolation threshold in ZnO. We believe that observed high temperature FM is primarily mediated by defects in the strained NPs. ZnO NPs of lower initial size show enhanced FM that may be attributed to size dependent doping effect.