bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical function evolution of ion-assisted ZrN films deposited by sputtering
Authors: Valerini D. , Signore M. A. , Rizzo A. , Tapfer L.
Published: October 2010

The optical functions (complex dielectric function, complex index of refraction, and complex conductivity) of sputtered zirconium nitride films are derived starting from optical reflectance measurements. Their evolution with the different bias voltages applied during the films growth is used to deduce information about the variations in the electronic structure influenced by a different oxygen and nitrogen content in the films. Improvement in the electrical conductivity is observed at increasing bias voltage due to a reduction in both oxygen contamination and nitrogen content. The separation of the different contributions (free conduction electrons and different electronic transitions) in the optical functions is achieved through the Drude–Lorentz model, allowing the detection of an unusual low-energy electronic transition in films grown at low bias voltages. Through considerations about the electronic structure and about the results coming from other characterization techniques, this transition can be ascribed to the presence of defects/impurities, nitrogen superstoichiometry, or oxygen contamination.
Fast and slow magnetosonic waves in two-dimensional spin-1/2 quantum plasma
Authors: Mushtaq A. , Vladimirov S. V.
Published: October 2010

Using the spin-1/2 resistive quantum magnetohydrodynamics model, linear and nonlinear relations for slow and fast magnetosonic modes are derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The plasma resistivity is shown to play a role of dissipation in the system. With the aid of tanh method the traveling wave solution of Kadomstev–Petviashvili–Burgers is obtained. The solution shows a general shock wave profile superposed by a perturbative solitary-wave contribution. The dynamics of fast and slow magnetosonic shock and soliton, respectively, in the presence and absence of dissipation is investigated with respect to electron spin magnetization, quantum diffraction, and plasma statistic. It is found that results obtained from the spin quantum plasmas differ significantly from the nonspin quantum plasmas. The relevance of the present work to dense astrophysical plasmas such as pulsar magnetosphere is pointed out.
Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb/Si: A Monte Carlo simulation
Authors: Du Hai-Feng , He Wei , Liu Hao-Liang , Sun Da-Li , Fang Ya-Peng , Gao Jian-Hua , Zhang Xiang-Qun , Cheng Zhao-Hua
Published: October 2010

Magnetic behaviors of Fe nanowires grown on 4° miscut Si(111) substrate with Pb buffer layers have been investigated by means of Monte Carlo method. A simple model is constructed, in which the Fe chains are assumed to be assemblies of single domain Fe nanoclusters with magnetostatic energy and exchange coupling energy. The coverage dependence of the magnetic ordering temperature TC of the system is discussed. By accurately calculating the magnetostatic energy of the Fe chains, the simulated results are in agreement with the experimental ones measured by in situ surface magneto-optical Kerr effect. In addition to the magnetostatic energy, the exchange coupling between the overlapping islands is also responsible for the ferromagnetic ordering of high coverage Fe chains at room temperature. Our model was able to predict the essential features of the system.
Stable plateau formation and Brillouin suppression in laser plasma
Authors: Mulser P. , Weng S. M.
Published: October 2010

Among the variety of ponderomotively induced density structures in laser produced plasmas in one dimension, it is shown by particle-in-cell simulations that the stable plateau formation at critical, subcritical, and above critical density is possible. Stimulated Brillouin backscattering is suppressed with increasing laser intensity.
Nonlinear kinetic description of Raman growth using an envelope code, and comparisons with Vlasov simulations
Authors: Bénisti Didier , Morice Olivier , Gremillet Laurent , Siminos Evangelos , Strozzi David J.
Published: October 2010

In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering in a uniform and collisionless plasma using envelope equations. We recall the derivation of these equations, as well as our theoretical predictions for each of the nonlinear kinetic terms, the precision of which having been carefully checked against Vlasov simulations. We particularly focus here on the numerical resolution of these equations, which requires the additional concept of “self-optimization” that we explain, and we describe the envelope code BRAMA that we used. As an application of our modeling, we present one-dimensional BRAMA simulations of stimulated Raman scattering which predict threshold intensities, as well as time scales for Raman growth above threshold, in very good agreement with those inferred from Vlasov simulations. Finally, we discuss the differences between our modeling and other published ones.
Compressive and rarefactive solitary waves in nonthermal two-component plasmas
Authors: Verheest Frank , Hellberg Manfred A.
Published: October 2010

Using a Sagdeev pseudopotential formalism where nonlinear structures are stationary in a comoving frame, large ion-acoustic solitary waves and double layers have been studied in plasmas with positive ions and nonthermal electrons. The velocity range of positive, compressive solitary waves is limited by the ion density reaching infinite compression, whereas negative, rarefactive solitary waves and double layers can exist when the electron nonthermality exceeds a certain minimum. There are even regions of coexistence, the limits of which can be elucidated by considering the properties of the special Sagdeev pseudopotential at the acoustic speed. In particular, when the compositional parameters and Mach numbers admit only compressive or rarefactive solitary structures, these have to be superacoustic, their amplitude vanishing at the acoustic speed. When both compressive and rarefactive modes can occur, one of them is Korteweg–de Vries (KdV)-like, the other having a non-KdV character, with a finite amplitude at the acoustic speed.
Phase-field simulations of viscous fingering in shear-thinning fluids
Authors: Nguyen Sébastien , Folch Roger , Verma Vijay K. , Henry Hervé , Plapp Mathis
Published: October 2010

A phase-field model for the Hele-Shaw flow of non-Newtonian fluids is developed. It extends a previous model for Newtonian fluids to a wide range of fluids with a shear-dependent viscosity. The model is applied to simulate viscous fingering in shear-thinning fluids and found to capture the complete crossover from the Newtonian regime at low-shear rate to the strongly shear-thinning regime. The width selection of a single steady-state finger is studied in detail for a two-plateau shear-thinning law (Carreau’s law) in both its weakly and strongly shear-thinning limits, and the results are related to the previous analyses. For power-law (Ostwald–de Waele) fluids in the strongly shear-thinning regime, good agreement with experimental data from the literature is obtained.
Diagnosing inertial confinement fusion gamma ray physics (invited)
Authors: Herrmann H. W. , Hoffman N. , Wilson D. C. , Stoeffl W. , Dauffy L. , Kim Y. H. , McEvoy A. , Young C. S. , Mack J. M. , Horsfield C. J. , Rubery M. , Miller E. K. , Ali Z. A.
Published: October 2010

The gamma reaction history (GRH) diagnostic is a multichannel, time-resolved, energy-thresholded γ-ray spectrometer that provides a high-bandwidth, direct-measurement of fusion reaction history in inertial confinement fusion implosion experiments. 16.75 MeV deuterium+tritium (DT) fusion γ-rays, with a branching ratio of the order of 10−5γ/(14 MeV n), are detected to determine fundamental burn parameters, such as nuclear bang time and burn width, critical to achieving ignition at the National Ignition Facility. During the tritium/hydrogen/deuterium ignition tuning campaign, an additional γ-ray line at 19.8 MeV, produced by hydrogen+tritium fusion with a branching ratio of unity, will increase the available γ-ray signal and may allow measurement of reacting fuel composition or ion temperature. Ablator areal density measurements with the GRH are also made possible by detection of 4.43 MeV γ-rays produced by inelastic scatter of DT fusion neutrons on C12 nuclei in the ablating plastic capsule material.
Wide-field turbulence imaging with beam emission spectroscopy
Authors: McKee G. R. , Fonck R. J. , Shafer M. W. , Uzun-Kaymak I. U. , Yan Z.
Published: October 2010

Imaging of the size, shape, time-averaged, and time-resolved dynamics of long-wavelength density turbulence structures is accomplished with an expanded, high-sensitivity, wide-field beam emission spectroscopy (BES) diagnostic on DIII-D. A 64-channel BES system is configured with an 8×8 grid of discrete channels that image an approximately 7×9 cm region at the outboard midplane. The grid covers multiple correlation lengths and each channel shape matches the measured radial-poloidal correlation length asymmetry of turbulent eddies. The wide field 8×8 imaging capability allows for sampling of essentially the full two-dimensional spatial correlation function for typical plasma conditions. The sampled area can be radially scanned over 0.4<r/a<1, including the core (ñ/n<1%), pedestal, and scrape-off-layer. The resulting time-resolved visualizations of turbulence and flows provide critical data on turbulence dynamics.
Probe pressure dependence of nanoscale capacitance-voltage characteristic for AlGaN/GaN heterostructures
Authors: Zhang Jihua , Zeng Huizhong , Zhang Min , Liu Wei , Zhou Zuofan , Chen Hongwei , Yang Chuanren , Zhang Wanli , Li Yanrong
Published: October 2010

This paper investigated the effect of atomic force microscopy probe pressure on capacitance-voltage (C-V) and two-dimensional electron gas (2DEG) characteristics. Based on the experimental results, first principles and charge control model calculations were carried out to explore the origin of the changes in C-V and 2DEG characteristics. It is found that the strain of AlGaN induced by the probe pressure was very limited, thus it did not change the C-V characteristic and 2DEG density. The change of threshold voltage and 2DEG density is mainly attributed to the variation of surface barrier height, which is sensitive to the gap between the probe and the sample. Therefore, to map the electronic properties distribution, one should adopt constant force mode to eliminate the effect of probe pressure.
Guiding of intense laser pulse in uniform plasmas and preformed plasma channels
Authors: Wang Jingwei , Yu Wei , Yu M. Y. , Lei A. L. , Wang Xin , Senecha V. K. , Wang X. G. , Murakami M. , Mima K.
Published: October 2010

Guiding of laser pulse in uniform plasmas and preformed plasma channels is investigated. The self-guiding mechanisms for these two cases are quite different. It is found that an intense laser pulse can be steadily self-guided in underdense plasmas with nearly a constant spot size if the self-consistently generated electron cavity has a sufficiently steep density gradient at the edge. In a preformed plasma channel, however, laser guiding is maintained mainly by the balance between the light diffraction and focusing. The latter is induced by the wall plasmas which greatly reduce the local dielectric constant. It is shown that the self-guiding of a laser pulse in uniform plasmas requires tens of terawatts power, but those that are in preformed channels can be realized with only a terawatt power.
From extended phase space dynamics to fluid theory
Authors: Zamanian Jens , Stefan Martin , Marklund Mattias , Brodin Gert
Published: October 2010

We derive a fluid theory for spin-1/2 particles starting from an extended kinetic model based on a spin-projected density matrix formalism. The evolution equation for the spin density is found to contain a pressurelike term. We give an example where this term is important by looking at a linear mode previously found in a spin kinetic model.
On the efficiency of intrinsic rotation generation in tokamaks
Authors: Kosuga Y. , Diamond P. H. , Gürcan Ö. D.
Published: October 2010

A theory of the efficiency of the plasma flow generation process is presented. A measure of the efficiency of plasma self-acceleration of mesoscale and mean flows from the heat flux is introduced by analogy with engines, using the entropy budget defined by thermal relaxation and flow generation. The efficiency is defined as the ratio of the entropy destruction rate due to flow generation to the entropy production rate due to ∇T relaxation (i.e., related to turbulent heat flux). The efficiencies for two different cases, i.e., for the generation of turbulent driven E×B shear flow (zonal flow) and for toroidal intrinsic rotation, are considered for a stationary state, achieved by balancing entropy production rate and destruction rate order by order in O(k∥/k⊥), where k is the wave number. The efficiency of intrinsic toroidal rotation is derived and shown to be eIR∼(Mach)th2∼0.01. The scaling of the efficiency of intrinsic rotation generation is also derived and shown to be ρ∗2(q2/ŝ2)(R2/LT2)=ρ∗2(Ls2/LT2), which suggests a machine size scaling and an unfavorable plasma current scaling which enters through the shear length.
Resonant enhancement of mode conversion in unmagnetized plasmas due to a periodic density modulation superimposed on a linear electron density profile
Authors: Yu Dae Jung , Kim Kihong , Lee Dong-Hun
Published: October 2010

Mode conversion of p-polarized electromagnetic waves into longitudinal plasma oscillations at resonance points in cold, unmagnetized, and stratified plasmas, where a small periodic density modulation is superimposed on a linear electron density profile, is theoretically studied. The mode conversion coefficient and the magnetic field distribution are calculated in a numerically exact manner using the invariant imbedding theory of mode conversion. It is found that resonant enhancement of mode conversion, which is sometimes as high as 100%, can be achieved by tuning the incident angle, the modulation period, or the wave frequency. This phenomenon is explained as due to the formation of a standing wave near the resonance point.
Optimization of laser parameters to obtain high-energy, high-quality electron beams through laser-plasma acceleration
Authors: Samant Sushil Arun , Sarkar Deepangkar , Upadhyay Ajay K. , Krishnagopal Srinivas , Jha Pallavi
Published: October 2010

The propagation of an intense (a0=3), short-pulse (L∼λp) laser through a homogeneous plasma has been investigated. Using two-dimensional simulations for a0=3, the pulse-length and spot-size at three different plasma densities were optimized in order to get a better quality beam in laser wakefield accelerator. The study reveals that with increasing pulse-length the acceleration increases, but after a certain pulse-length (L>0.23λp) the emittance blows-up unacceptably. For spot-sizes less than that given by kp0rs=2a0, trapping is poor or nonexistent, and the optimal spot-size is larger. The deviation of the optimal spot-size from this formula increases as the density decreases. The efficacy of these two-dimensional simulations has been validated by running three-dimensional simulations at the highest density. It has been shown that good quality GeV-class beams can be obtained at plasma densities of ∼1018 cm−3. The quality of the beam can be substantially improved by selecting only the high-energy peak; in this fashion an energy-spread of better than 1% and a current in tens of kA can be achieved, which are important for applications such as free-electron lasers.
Effects of matching network on the hysteresis during E and H mode transitions in argon inductively coupled plasma
Authors: Gao Fei , Zhao Shu-Xia , Li Xiao-Song , Wang You-Nian
Published: October 2010

An experimental investigation of the hysteresis during the E (capacitive coupling) and H mode (inductive coupling) transitions at various matching situation in argon inductively coupled plasma is reported. At high pressure, the results show two hysteresis loops involved the plasma density, applied power, and forward power, as well as the electrical parameters in the discharge circuit, when the series capacitance is cycled. The measured electron density versus applied power shows that the hysteresis loop shrinks with the decrease of the matching capacitance, and the same trend is discovered on the input current, voltage, and phase angle. In addition, for the case of small capacitance, the current (or voltage) jumps to a low value when the discharge passes through the E to H mode transition regime. Contrarily, for the case of large capacitance, the current jumps to a high value while the voltage is almost constant. The evolution characteristics of the plasma and circuit parameters observed imply that the nonlinear behavior of the matching situation may be one of the determined factors for hysteresis.
Electron cyclotron emission diagnostic for ITER
Authors: Rowan W. , Austin M. , Beno J. , Ellis R. , Feder R. , Ouroua A. , Patel A. , Phillips P.
Published: October 2010

Electron temperature measurements and electron thermal transport inferences will be critical to the nonactive and deuterium phases of ITER operation and will take on added importance during the alpha heating phase. The diagnostic must meet stringent criteria on spatial coverage and spatial resolution during full field operation. During the early phases of operation, it must operate equally well at half field. The key to the diagnostic is the front end design. It consists of a quasioptical antenna and a pair of calibration sources. The radial resolution of the diagnostic is less than 0.06 m. The spatial coverage extends at least from the core to the separatrix with first harmonic O-mode being used for the core and second harmonic X-mode being used for the pedestal. The instrumentation used for the core measurement at full field can be used for detection at half field by changing the detected polarization. Intermediate fields are accessible. The electron cyclotron emission systems require in situ calibration, which is provided by a novel hot calibration source. The critical component for the hot calibration source, the emissive surface, has been successfully tested. A prototype hot calibration source has been designed, making use of extensive thermal and mechanical modeling.
Fast neutron-gamma discrimination on neutron emission profile measurement on JT-60U
Authors: Ishii K. , Shinohara K. , Ishikawa M. , Baba M. , Isobe M. , Okamoto A. , Kitajima S. , Sasao M.
Published: October 2010

A digital signal processing (DSP) system is applied to stilbene scintillation detectors of the multichannel neutron emission profile monitor in JT-60U. Automatic analysis of the neutron-γ pulse shape discrimination is a key issue to diminish the processing time in the DSP system, and it has been applied using the two-dimensional (2D) map. Linear discriminant function is used to determine the dividing line between neutron events and γ-ray events on a 2D map. In order to verify the validity of the dividing line determination, the pulse shape discrimination quality is evaluated. As a result, the γ-ray contamination in most of the beam heating phase was negligible compared with the statistical error with 10 ms time resolution.
A digital lock-in upgrade of the motional Stark effect diagnostic on DIII-D
Authors: King J. D. , Makowski M. A. , Holcomb C. T. , Allen S. L. , Geer R. , Meyer W. H. , Hill D. N. , Pham D. , Morse E. C.
Published: October 2010

The use of lock-in amplifiers for phase sensitive detection of motional Stark effect (MSE) diagnostic signals is of critical importance to real-time internal current profile measurements in tokamak plasmas. A digital lock-in (DLI) upgrade utilizing field programable gate array firmware has been installed on the MSE system of the DIII-D tokamak for the eventual replacement of largely obsolete analog units. While the new digital system has shown a small reduction in electronic noise over the analog, the main advantages are reduced cost, hardware simplicity, compact size, and phase tracking during plasma operations. DLI recovery of MSE polarization angles was accomplished through use of reference processing to produce only photoelastic modulator (PEM) second harmonic frequencies and electronic signal processing to maximize the fidelity of the recovered signal. A simplified discrete analytical solution was found that accurately describes the new DLI hardware. The DLI algorithm was found to cause a prohibitively large oscillating artifact atop the demodulated signal. The artifact was caused by the accumulator interval not containing an exact integer number of PEM multiplier periods. Successful MSE measurements require the minimization of this oscillating artifact amplitude. The analytical solution was used to select an appropriate accumulator interval that both reduces the artifact and maintains the greatest temporal resolution possible. Sample EFIT equilibria reconstructions and corresponding safety factor profiles showed very close agreement between the analog and digital lock-ins.
Charge exchange spectroscopy system calibration for ion temperature measurement in KSTAR
Authors: Ko Won-Ha , Lee Hyungho , Seo Dongcheol , Kwon Myeun
Published: October 2010

The charge exchange spectroscopy (CES) system including collection assemblies, lens design, and cassettes for the KSTAR experiment was installed to obtain profiles of the ion temperature and the toroidal rotation velocity from charge exchange emission between plasma ions and beam neutrals near the plasma axis by using a modulated neutral beam and a background system. We can measure the charge exchange spectra of an impurity line such as the 529 nm line of carbon VI to get ion temperature and rotation profiles in KSTAR. The CES and background systems will have absolute intensity and spectral calibrations using a calibrated source and various spectral lamps. The calibration was done inside the tokamak after all CES systems are installed and the optical systems are slid into the cassettes. This requires that the diagnostic systems are installed near the vacuum vessel inside the cryostat maintaining the superconducting state of the superconducting coils. Repeated spectral calibrations of the spectrometer and charge coupled device for CES will be made in the diagnostic room during the experimental campaign. We show a detailed description of the KSTAR CES system, how to calibrate, and the results of calibration.
The impact of contaminants on laser-driven light ion acceleration
Authors: Petrov G. M. , Willingale L. , Davis J. , Petrova Tz. , Maksimchuk A. , Krushelnick K.
Published: October 2010

The impact of contaminants on laser-driven ion acceleration is investigated using particle-in-cell simulations. The conventional ion acceleration mechanism, target normal sheath acceleration, has been revisited for targets with proton-rich contaminants in the form of water vapor. The targets considered have a deuterated plastic layer on the rear surface of an aluminum target, and the influence of the contaminant layer on the deuteron acceleration is investigated. In the early stage of ion acceleration, the space-charge electrostatic field on the rear target surface accelerates only the outermost, proton-rich layer of ions, which inhibits the deuteron acceleration by shielding it from the field. When the proton layer is depleted, the deuterons become exposed to the space-charge field and are promptly accelerated. This scenario was tested with a two-dimensional particle-in-cell simulation model by varying the contaminant layer thickness and laser fluence (laser energy per unit area). For laser fluences Flaser<1 J/μm2, the contamination layer over the surface inhibits the deuteron acceleration from the rear surface, while in the opposite case of laser fluences Flaser>1 J/μm2 deuterons and heavier ions can be successfully accelerated with conversion efficiency of laser energy into ions of more than 1%. Experimental data from a 6 μm thick aluminum foil coated with a 1 μm deuterated plastic layer on the back surface are suggestive of the detrimental role of contaminants on deuteron acceleration.
Impacts of recombination at the surface and in the substrate on carrier lifetimes of n-type 4H–SiC epilayers
Authors: Kimoto Tsunenobu , Hiyoshi Toru , Hayashi Toshihiko , Suda Jun
Published: October 2010

After remarkable reduction in the Z1/2 center in n-type 4H–SiC epilayers, the measured carrier lifetimes can be severely affected by other recombination paths. Impacts of carrier recombination at the surface as well as in the substrate are investigated in detail by using numerical simulation based on a diffusion equation. The simulation reveals that a very thick (>100 μm) epilayer is required for accurate measurement of carrier lifetimes if the bulk lifetime in the epilayer is longer than several microsecond, due to the extremely short lifetimes in the substrate. The fast decay often observed at the initial stage of decay curves can be explained by fast recombination at the surface and in the substrate. In experiments, the carrier lifetime is improved from 0.69 to 9.5 μs by reducing the Z1/2 center via two-step thermal treatment (thermal oxidation and Ar annealing) for a 148-μm-thick n-type epilayer. This lifetime must be still, to large extent, affected by the recombination at the surface and in the substrate, and the real bulk lifetime may be much longer. The carrier recombination paths and their impacts on the decay curves are discussed.
Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro
Authors: Petrantoni M. , Rossi C. , Salvagnac L. , Conédéra V. , Estève A. , Tenailleau C. , Alphonse P. , Chabal Y. J.
Published: October 2010

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.
Design and test of miniaturized glass ceramics HeNe laser with frequency and intensity simultaneously stabilized
Authors: Wei Zhimeng , Yang Kaiyong , Lu Guangfeng , Long Xingwu , Zhang Bin , Xu Yunong
Published: October 2010

A miniaturized HeNe laser with intensity and frequency simultaneously stabilized is described. The laser uses a monoblock glass ceramics as its tube to construct an improved steady structure. The closed loop cavity length control system stabilizes its frequency and the discharge current regulating system stabilizes its intensity. The electronic system integrating power supply and stabilization system is designed within two small circuit boards. The laser tube and circuit boards are assembled into a small package with dimensions of 180 mm×100 mm×150 mm. The laser outputs s-polarized light at wavelength of 632.99 nm with power of 0.44 mW. Test results show that its frequency stability can reach 8.4×10−11 (1s Allan variance over 3 h) and frequency reproducibility at 1.3×10−8. The laser’s intensity stability is 0.011% over 9 h.
Consideration of the mechanism of microwave emission due to material destruction
Authors: Takano Tadashi , Ikeda Hirokazu , Maeda Takashi
Published: October 2010

Microwave emission due to material destruction by hypervelocity impact with several kilometers per second was found at 2 and 22 GHz, and its power was calibrated in the laboratory for the first time ever. In this paper, we first summarize the experimental results in relation to the mechanism of microwave emission. We then propose three kinds of hypotheses on the mechanism, which are based on the dynamic relative motion of an atom’s nucleus and the outermost electron and lead to dipole radiation. The deduced equation represents the power dependence on the target’s thickness, which agrees well with the experimental result. The models were then numerically analyzed in consideration of the experimental data. In the most promising model, a projectile molecule flicks the nucleus out and the outermost electron is left out of the orbit of the atom. Accordingly, the material is polarized or ionized to form an impulsive dipole, which leads to microwave emission. This model is compatible with material ionization by mechanical excitation, such as rubbing and peeling, or triboelectricity. The calculated energy shows good agreement with the experimental value. On the other hand, if the outermost electron remains within the gravity field of the nucleus, the calculated and experimental results do not agree with each other.
Pressure-induced phase transition in cubic Lu2O3
Authors: Jiang Sheng , Liu Jing , Lin Chuanlong , Bai Ligang , Xiao Wansheng , Zhang Yufeng , Zhang Dechun , Li Xiaodong , Li Yanchun , Tang Lingyun
Published: October 2010

The phase transition in cubic Lu2O3 has been investigated by angle dispersive x-ray diffraction and Raman scattering in a diamond anvil cell up to 46.8 GPa and 40.2 GPa, respectively. The diffraction data indicated that a phase transition from the cubic to a monoclinic structure started at 12.7 GPa and completed at 18.2 GPa. This high pressure monoclinic phase is stable up to at least 46.8 GPa and can be quenched to ambient conditions. This irreversible cubic to monoclinic structural transformation has also been confirmed by Raman scattering measurements. A third-order Birch–Murnaghan fit based on the observed pressure-volume data yields a zero pressure bulk modulus of B0=214(6) GPa, its pressure derivative B0′=9(1) for the low-pressure cubic phase; and B0=218(13) GPa, B0′=2.3(3) for the high pressure monoclinic phase, respectively. The mode Grüneisen parameters of different Raman modes for both cubic and monoclinic phases have also been determined.
Physical loss mechanisms for resonant acoustical waves in boron doped poly-SiGe deposited with hydrogen dilution
Authors: Stoffels Steve , Autizi Enrico , Van Hoof Rita , Severi Simone , Puers Robert , Witvrouw Ann , Tilmans Harrie A. C.
Published: October 2010

In this paper, the physical loss mechanisms in boron doped poly-SiGe are analyzed theoretically and experimentally. The phonon losses were calculated theoretically for different germanium and doping concentrations. The theoretical analysis showed that Akhiezer damping sets a fundamental lower limit to the internal damping. Calculated limits for the f×Q due to Akhiezer damping were ∼1×1014 Hz for SiGe with low Ge content and ∼2×1013 Hz for SiGe with high Ge content. However, in the experiments it was found that an internal friction loss mechanism limits the maximum achievable f×Q in our material to 3×1012 at a frequency of 130 MHz. Experimentally the loss mechanisms were studied further by preparing SiGe layers with different Ge/H/B content. The acoustical losses were measured by fabricating a micromechanical resonator from the layers. The measurements identified a thermally activated loss mechanism. By studying the microstructure of the SiGe layers, we identified interface defects and interstitial as the most important loss mechanisms. Furthermore, the experiments show that at high frequencies (>130 MHz) the achievable f×Q-products of SiGe are close to the values, which can be achieved with single crystal materials.
Alfvenic modes in a bi-Maxwellian electron-ion plasma
Authors: Bashir M. F. , Iqbal Z. , Aslam I. , Murtaza G.
Published: October 2010

Employing linearized Vlasov–Maxwell system, we derive a generalized dielectric tensor for a magnetized nonrelativistic bi-Maxwellian electron-ion plasma. Assuming low frequency waves in a low β plasma, a new dispersion relation describing oblique propagation of the Alfvenic modes is determined, incorporating the temperature anisotropies of both the electrons and ions and their finite Larmor radii effects. From the resulting dispersion relation for kinetic Alfven waves, analytical expressions are determined for both the kinetic (vt∥i⪡ω/k∥⪡vt∥e and me/mi⪡β⪡1) and the inertial (ω/k∥⪢vt∥e,i and β⪡me/mi) regimes. We observe that in both cases, the Alfvenic modes stand modified due to the acoustic effect arising from the temperature anisotropy, which may enhance or reduce the Alfven speed depending on the strength and signature of the anisotropies. A number of special cases are also retrieved under appropriate conditions.
Formation of void lattice after annealing of Ge quantum dot lattice in alumina matrix
Authors: Pinto S. R. C. , Rolo A. G. , Gomes M. J. M. , Ivanda M. , Bogdanović-Radović I. , Grenzer J. , Mücklich A. , Barber D. J. , Bernstorff S. , Buljan M.
Published: October 2010

We report on the formation of a regularly ordered void lattice with a void size of about 4 nm in an alumina matrix. The voids were formed by thermal treatment of a well-ordered three-dimensional Ge quantum dot lattice formed earlier by self-assembled growth in an alumina matrix during magnetron sputtering codeposition of Ge+Al2O3. During the subsequent annealing the germanium atoms were lost from the film and so voids were produced. The positions of the voids are ordered in the same way as the Ge quantum dots that were present before annealing, while their sizes can be controlled by the deposition parameters.
Microwave imaging reflectometry studies for turbulence diagnostics on KSTAR
Authors: Park H. K. , Hong I. , Kim M. , Yun G. S. , Lee W. , Kim J. , Tobias B. , Domier C. W. , Luhmann N. C. , Kim K. W.
Published: October 2010

The first prototype microwave imaging reflectometry (MIR) system [H. Park et al., Rev. Sci. Instrum. 74, 4239 (2004)] clearly demonstrated the shortcomings of conventional reflectometry when the probe beam encountered a large amplitude and/or high fluctuation wavenumber at the reflection layer in laboratory tests, the distinctive advantages shown in these tests were not fully realized in the plasma operation. To understand the discrepancies, the MIR system performance has been thoroughly investigated at POSTECH. In this paper, a possible cause of the MIR performance degradation on TEXTOR will be presented together with a concept of multifrequency MIR system design that will be developed for KSTAR.
Experimental setup for tungsten transport studies at the NSTX tokamak
Authors: Clementson J. , Beiersdorfer P. , Roquemore A. L. , Skinner C. H. , Mansfield D. K. , Hartzfeld K. , Lepson J. K.
Published: October 2010

Tungsten particles have been introduced into the National Spherical Torus Experiment (NSTX) in Princeton with the purpose to investigate the effects of tungsten injection on subsequent plasma discharges. An experimental setup for the study of tungsten particle transport is described where the particles are introduced into the tokamak using a modified particle dropper, otherwise used for lithium-powder injection. An initial test employing a grazing-incidence extreme ultraviolet spectrometer demonstrates that the tungsten-transport setup could serve to infer particle transport from the edge to the hot central plasmas of NSTX.
Electronic effect on hydrogen brittleness of austenitic steels
Authors: Gavriljuk V. G. , Shanina B. D. , Shyvanyuk V. N. , Teus S. M.
Published: October 2010

Hydrogen effects in austenitic steels are studied using the ab initio calculations of the electronic structure, conduction electron spin resonance, internal friction, and mechanical tests. It is shown that the hydrogen-caused elastic shielding of dislocations is not sufficient for interpretation of hydrogen-enhanced localized plasticity (HELP). Similar effects of hydrogen and nitrogen and the opposite effect of carbon on dislocation mobility are demonstrated, which cannot be explained within the framework of continuum mechanics. An interpretation of hydrogen embrittlement in terms of the hydrogen-increased concentration of free (conduction) electrons is proposed. Based on the electronic approach to the HELP phenomenon, practical recommendations for increase in hydrogen resistance of austenitic steels are made and tested.
Improved time-frequency analysis of ASDEX Upgrade reflectometry data using the reassigned spectrogram technique
Authors: Varela P. , Silva A. , da Silva F. , da Graça S. , Manso M. E. , Conway G. D. ,   the ASDEX Upgrade Team
Published: October 2010

The spectrogram is one of the best-known time-frequency distributions suitable to analyze signals whose energy varies both in time and frequency. In reflectometry, it has been used to obtain the frequency content of FM-CW signals for density profile inversion and also to study plasma density fluctuations from swept and fixed frequency data. Being implemented via the short-time Fourier transform, the spectrogram is limited in resolution, and for that reason several methods have been developed to overcome this problem. Among those, we focus on the reassigned spectrogram technique that is both easily automated and computationally efficient requiring only the calculation of two additional spectrograms. In each time-frequency window, the technique reallocates the spectrogram coordinates to the region that most contributes to the signal energy. The application to ASDEX Upgrade reflectometry data results in better energy concentration and improved localization of the spectral content of the reflected signals. When combined with the automatic (data driven) window length spectrogram, this technique provides improved profile accuracy, in particular, in regions where frequency content varies most rapidly such as the edge pedestal shoulder.
Optimization of a bolometer detector for ITER based on Pt absorber on SiN membrane
Authors: Meister H. , Eich T. , Endstrasser N. , Giannone L. , Kannamüller M. , Kling A. , Koll J. , Trautmann T. ,   ASDEX Upgrade Team, Detemple P. , Schmitt S.
Published: October 2010

Any plasma diagnostic in ITER must be able to operate at temperatures in excess of 200 °C and neutron loads corresponding to 0.1 dpa over its lifetime. To achieve this aim for the bolometer diagnostic, a miniaturized metal resistor bolometer detector based on Pt absorbers galvanically deposited on SiN membranes is being developed. The first two generations of detectors featured up to 4.5 μm thick absorbers. Results from laboratory tests are presented characterizing the dependence of their calibration constants under thermal loads up to 450 °C. Several detectors have been tested in ASDEX Upgrade providing reliable data but also pointing out the need for further optimization. A laser trimming procedure has been implemented to reduce the mismatch in meander resistances below 1% for one detector and the thermal drifts from this mismatch.
Constitutive modeling of shock response of phase-transforming and porous materials with strength
Authors: Resnyansky A. D.
Published: October 2010

The paper analyzes constitutive behavior of phase-transforming materials and metal powders loaded by shock waves. A two-phase material model developed earlier is extended to the case of materials with strength. Available experimental free surface velocities of iron samples under the α-ε phase transition and shock velocity data for porous aluminum and copper are analyzed numerically with the present model. The phase transition hysteresis is demonstrated by numerical analysis of experimental free surface velocities. Possible role of the martensitic mechanism in the hysteresis is emphasized. The calculated anomalous Hugoniots as well as pressure equilibrium (PE) and pressure-temperature equilibrium (PTE) Hugoniots are compared with available experiments for aluminum and copper powders. It is argued that a large nonequilibrium interphase heat transfer zone for aluminum powders results in a scatter of experimental Hugoniot points between the PE and PTE Hugoniots in low pressure region. In turn, in high pressure region, the effect of strength on porous Hugoniot may increase with porosity due to an extra dissipation, which improves description of experiments for an extremely porous aluminum.
In situ measurement of the bonded film thickness of Z-Tetraol lubricant on magnetic recording media
Authors: Zhu Lei , Li Feng
Published: October 2010

Currently, the bonded film thickness of perfluoropolyether lubricant on top of magnetic recording media is measured by a two-step process. First, the media disk has to be rinsed thoroughly using a fluorocarbon solvent (for instance, Vetrel) to remove the mobile lubricant. Second, the thickness of the remaining lubricant on the media surface which is regarded as the bonded lubricant thickness is then measured either by Fourier transform infrared spectroscopy (FTIR) or electron spectroscopy for chemical analysis. As the total lubricant thickness approaches single molecular dimension (∼10 Å), current methods face tremendous challenge on the accuracy and sensitivity of the measurement. We studied the spectral characteristics responding to the lubricant bonding with the carbon overcoat by the time-of-flight secondary ion mass spectra and proposed to use the peak area ratio (C3H2F/C3H5O and C4H10O/C3H6O2) to characterize the bonded Z-Tetraol lubricant that produces a direct bonded lubricant thickness measurement without the need to remove the mobile lubricant with a solvent. After taking the background signal of disks prior to bonding by UV irradiation into account, this method becomes independent of the total lubricant thickness as well as shows good correlation linearity (R2∼87%) with the current FTIR method for the ratio of C4H10O/C3H6O2.
Appearance of a correlation between the Hall coefficient and electrical resistivity upon dihydrogenation of yttrium
Authors: Sakai M. , Kodama D. , Ito S. , Ito M. , Nakamura O. , Hasegawa S. , Kitajima A. , Oshima A.
Published: October 2010

To shed light on the correlation between the Hall coefficient (RH) and electrical resistivity (ρ), we performed simultaneous measurements of these two transport coefficients in fcc dihydride phase of yttrium (YHx), having H/Y values ranging from 1.73 to 2.04. Unlike the typical behavior of metals, an approximately linear relationship was observed between RH and ρ at room temperature after dihydrogenation of yttrium. Interpretation of this relationship, based on the Boltzmann–Bloch scheme, reveals that the transverse (cyclotron) relaxation rate (1/τc) of the carriers is relatively insensitive to the generation of hydrogen defects in the dihydride phase of yttrium, unlike the longitudinal relaxation rate (1/τ), which is affected by the presence of hydrogen defect. Low-temperature (77 K) measurements of RH and ρ on the same samples show that the approximately linear relationship observed at room temperature disappears but a certain nonlinear relationship may exist at 77 K.
Modeling of the plasma generated in a rarefied hypersonic shock layer
Authors: Farbar Erin D. , Boyd Iain D.
Published: October 2010

In this study, a rigorous numerical model is developed to simulate the plasma generated in a rarefied, hypersonic shock layer. The model uses the direct simulation Monte Carlo (DSMC) method to treat the particle collisions and the particle-in-cell (PIC) method to simulate the plasma dynamics in a self-consistent manner. The model is applied to compute the flow along the stagnation streamline in front of a blunt body reentering the Earth’s atmosphere at very high velocity. Results from the rigorous DSMC-PIC model are compared directly to the standard DSMC modeling approach that uses the ambipolar diffusion approximation to simulate the plasma dynamics. It is demonstrated that the self-consistent computation of the plasma dynamics using the rigorous DSMC-PIC model captures many physical phenomena not accurately predicted by the standard modeling approach. These computations represent the first assessment of the validity of the ambipolar diffusion approximation when predicting the rarefied plasma generated in a hypersonic shock layer.
Real-time counting of single electron tunneling through a T-shaped double quantum dot system
Authors: Luo JunYan , Wang Shi-Kuan , He Xiao-Ling , Li Xin-Qi , Yan YiJing
Published: October 2010

Real-time detection of single electron tunneling through a T-shaped double quantum dot is simulated, based on a Monte Carlo scheme. The double dot is embedded in a dissipative environment and the presence of electrons on the double dot is detected with a nearby quantum point contact. We demonstrate directly the bunching behavior in electron transport, which leads eventually to a super-Poissonian noise. Particularly, in the context of full counting statistics, we investigate the essential difference between the dephasing mechanisms induced by the quantum point contact detection and the coupling to the external phonon bath. A number of intriguing noise features associated with various transport mechanisms are revealed.
The dielectric response of La0.5Ca0.5−xSrxMnO3 (0.1≤x≤0.4) manganites with different magnetic ground states
Authors: Dhiman Indu , Deshpande S. K. , Das A.
Published: October 2010

The dielectric behavior of half doped manganites La0.5Ca0.5−xSrxMnO3 (0.1≤x≤0.4) with varying magnetic ground states has been studied. The real part of relative permittivity as a function of temperature ε′(T), exhibits a maximum around the ferromagnetic (TC) and charge ordering transition (TCO) temperatures accompanied with high dielectric losses. The activation energies obtained for x=0.1 and 0.3 samples below TCO are the same ∼0.12 eV, whereas the relaxation time constant varies in the range 2.8×10−9 s–6.03×10−11 s. In contrast to samples having x≤0.3, for x=0.4 doping, the dielectric permittivity exhibits a strong temperature dependence in the vicinity of magnetic phase transitions. This behavior may be correlated with the presence of competing magnetic interactions (magnetic polarons) close to the magnetic transitions.
Colossal thermal-mechanical actuation via phase transition in single-crystal VO2 microcantilevers
Authors: Cao Jinbo , Fan Wen , Zhou Qin , Sheu Erica , Liu Aiwen , Barrett C. , Wu J.
Published: October 2010

The spontaneous strain associated with the structural change in the metal-insulator transition in VO2 is orders of magnitude higher than thermal expansion mismatch used in bimetallic strips. Here we show that this strain can be leveraged to thermally activate bending of crystalline VO2-based bilayer microcantilevers at extremely large curvatures, making them suitable for thermal sensors, energy transducers and actuators with unprecedented sensitivities. The single-crystallinity, deposition conditions, and postdeposition treatments were utilized to control the metal-insulator domain structure along the cantilever, by which we achieved bending curvatures a few hundred times higher than conventional bilayer cantilevers with the same geometry.