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  • Springer Nature  (79)
  • Oxford University Press  (72)
  • American Institute of Physics (AIP)  (69)
  • 2000-2004  (218)
  • 1945-1949  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Influence of the biased electrode on the plasma potential in ECRIS : Papers from the Ninth International Conference on Ion Sources (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 623-625 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Dedicated experiments have been carried out at the Frankfurt 14 GHz electron cyclotron resonance ion source (ECRIS) by using a special double biased-electrode assembly, which consists of a conventional disk electrode and a separately biased ring electrode installed in front of it. In this assembly, the ring can be used to modulate the fluxes to the disk and allows a detailed study of the role of secondary electron fluxes in ECRIS operation. It was found that these fluxes contribute more than 50% to the total disk currents. However, blocking them did not result in a drop in the extracted ion currents. Instead, it was observed that, under certain operational conditions, the injection of secondary electrons results in a decrease in the extracted currents by up to 20%. Parallel to the double disk measurements, Langmuir probe measurements have been performed close to the position of Bmax. From the probe characteristics, plasma potentials were determined to be about +30 V at the conditions of the experiment. Applying a negative voltage to the double disk electrodes leads to a decrease of the plasma potential by approximately 5 V. Changes in the plasma shape were observed when the biased electrode voltage was changed. We conclude that the main effect of the biased electrode is a decrease of the plasma potential by reflecting a sufficient amount of electrons back to plasma, which otherwise would have been lost. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1431700
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  • 2
    Electronic Resource
    Electronic Resource
    Light scattering from (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 with the tungsten bronze structure: An analogy with relaxor ferroelectrics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1671-1678 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Brillouin and Raman scattering from a complex single crystal from the tungsten–bronze family, (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 doped with Cu2+ (KNSBN:Cu), have been comparatively studied in a wide temperature range around the ferroelectric transition. Step-like anomalies in hypersonic velocity and damping confirm the first-order structural transition. These anomalies look like some perturbations on the high-temperature slopes of both a broad dip in sound velocity and a broad maximum in damping that develop in a wide temperature range. The acoustic behavior of KNSBN:Cu does not simply follow the Landau theory prediction valid for many ferroelectrics. Instead it resembles that of relaxors, to which the KNSBN:Cu behavior is analogous intrinsically. The total intensity of the Raman spectra as well as the intensity of separate internal and external vibrations and their width correlate with acoustic anomalies, namely there are step-like drops at the same temperature as the first-order transition and a broad range where the intensity is drastically increased. All these broad anomalies imply the existence of a wide preceding phase in respect to the relaxor ferroelectric state. Unusual properties of this preceding phase are discussed as well as the phase diagram relation to the dynamical evolution of other relaxors from the perovskite family, such as PbMg1/3Nb2/3O3 and Na1/2Ba1/2TiO3. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337923
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  • 3
    Electronic Resource
    Electronic Resource
    Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1911-1918 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-beta, low-aspect-ratio ("compact") stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2–4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A β=4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at β=4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874015
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  • 4
    Electronic Resource
    Electronic Resource
    Transitionless enhanced confinement and the role of radial electric field shear (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 615-625 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evidence is presented for the role of radial electric field shear in enhanced confinement regimes attained without sharp bifurcations or transitions. Temperature scans at constant density, created in the reheat phase following deuterium pellet injection into supershot plasmas in the Tokamak Fusion Test Reactor [J. D. Strachan, et al., Phys. Rev. Lett. 58, 1004 (1987)] are simulated using a physics-based transport model. The slow reheat of the ion temperature profile, during which the temperature nearly doubles, is not explained by relatively comprehensive models of transport due to Ion Temperature Gradient Driven Turbulence (ITGDT), which depends primarily on the (unchanging) electron density gradient. An extended model, including the suppression of toroidal ITGDT by self-consistent radial electric field shear, does reproduce the reheat phase. The extended reheat at constant density is observed in supershot but not L-Mode plasmas. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873867
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  • 5
    Electronic Resource
    Electronic Resource
    Erratum: "Understanding and control of transport in advanced tokamak regimes in DIII-D" [Phys. Plasmas 7, 1959 (2000)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3480-3480 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: © American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874221
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  • 6
    Electronic Resource
    Electronic Resource
    Understanding and control of transport in Advanced Tokamak regimes in DIII-D (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1959-1967 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport phenomena are studied in Advanced Tokamak (AT) regimes in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomics Energy Agency, Vienna, 1987), Vol. I, p. 159], with the goal of developing understanding and control during each of three phases: Formation of the internal transport barrier (ITB) with counter neutral beam injection taking place when the heating power exceeds a threshold value of about 9 MW, contrasting to co-NBI injection, where Pthreshold〈2.5 MW. Expansion of the ITB is enhanced compared to similar co-injected discharges. Both differences are believed to arise from modification of the E×B shear dynamics when the sign of the rotation contribution is reversed. Sustainment of an AT regime with βNH89=9 for 16 confinement times has been accomplished in a discharge combining an ELMing H-mode (edge localized, high confinement mode) edge and an ITB, and exhibiting ion thermal transport down to 2–3 times neoclassical. The microinstabilities usually associated with ion thermal transport are predicted stable, implying that another mechanism limits performance. High frequency magnetohydrodynamic (MHD) activity is identified as the probable cause. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874176
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular beam epitaxially grown n type Hg0.80Cd0.20Te(112)B using iodine (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 451-455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The molecular beam epitaxial growth and n type doping of Hg0.80Cd0.20Te(112)B have been investigated. The surface morphology has been determined via atomic force microscopy and is appreciably different from that of the (001) orientation; long ridges and trenches are observed whose height difference is considerably less than that of the nearly elliptically shaped mounds found in (001) alloys. The mobility has been optimized with regard to growth parameters such as the Hg/Te flux ratio resulting in a maximum value of 4.0±0.6×105 cm2/(V s) for an undoped sample at low temperatures. n type Hg0.80Cd0.20Te(112)B has been grown using iodine in the form of CdI2 as a dopant. The maximum electron concentration due to iodine doping has been determined after an Hg vacancy anneal to be 4.2±0.7×1018 cm−3. Typical mobilities at low temperatures are 4.0×104 and 1.0×105 cm2/(V s) for electron concentration levels of 1.0×1017 and 5.0×1016 cm−3, respectively. By means of secondary ion mass spectroscopy the iodine concentration has been determined and hence the degree of activation. The electron concentration is proportional to that of iodine with a 100% electrical activation for concentrations up to (approximate)1018 cm−3. At higher concentrations compensation is observed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1423770
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  • 8
    Electronic Resource
    Electronic Resource
    Physical and electrical characterization of Hafnium oxide and Hafnium silicate sputtered films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6466-6475 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar atmosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the silane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temperatures of 22 °C and 500 °C. The chemical composition of the films was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by transmission electron microscopy (TEM) and the electrical properties were measured with capacitance–voltage and current–voltage measurements using aluminum gate capacitors. TEM and electrical measurement showed that a SiO2 interfacial layer of about 3 nm formed at the Si interface due to the oxidizing sputter ambient. This precluded the growth of Hf based high-K films with small equivalent thickness. After correction for the interfacial oxide layer, the dielectric constant was found to decrease from about 21 for Hf oxide to about 4–5 for the Hafnium silicates with low Hf content (3 at. % Hf and 32 at. % Si). The optical band gap was found to increase from 5.8 eV for Hf oxide to about 7 eV for the silicate films. After annealing at 1000 °C followed by a 300 °C postmetallization anneal, negligible flat band voltage shift were measured on hafnium silicate films and good interface passivation was observed. However, leakage currents increased due to the high temperature processing. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1417991
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetoacoustics in low dimensional spin systems in pulsed magnetic fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7055-7057 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on sound wave propagation in pulsed fields up to 50 T for CsCuCl3 and (VO)2P2O7. Sound velocity and attenuation exhibit anomalies at the field induced spin transitions at low temperatures. In CsCuCl3 we observe step-like anomalies in sound velocity and pronounced peaks in attenuation at the saturation field (34 T at 1.5 K) and broader anomalies at the commensurate-incommensurate transition (14–17 T). In (VO)2P2O7 we observe a strong anomaly at the critical field when the lowest triplet branch crosses the singlet ground state (27 T at 1.6 K). All these experiments give important information on the spin state in high magnetic fields of these low dimensional spin systems and on the spin-phonon coupling. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372929
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  • 10
    Electronic Resource
    Electronic Resource
    Miniaturization and integration of photoacoustic detection (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1555-1563 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoacoustic spectroscopy is an absorption spectroscopy technique that is currently used for low-level gas detection and catalyst characterization. It is a promising technique for chemical analysis in mesoscale analysis systems because the detection limit scales favorably with miniaturization. This work focuses on the scaling properties of photoacoustic spectroscopy, and on the miniaturization of gas-phase photoacoustic detection of propane in a nitrogen ambient. The detection system is modeled with a transmission line analogy, which is verified experimentally. The model includes the effects of acoustic leaks and absorption saturation. These two phenomena degrade the performance of the photoacoustic detector and must be controlled to realize the scaling advantages of photoacoustic systems. The miniature brass cells used to verify the model employ hearing aid microphones and optical excitation from a mechanically chopped, 3.39 μm He–Ne laser, transmitted into the cells with an optical fiber. These cells are able to detect 10 ppm of propane in nitrogen (a signal level of ∼1 Pa/W). We also describe the development of a miniaturized photoacoustic system formed by microfabrication. In this case, the pressure-driven deflection of the detection membrane is measured optically. These systems show that photoacoustic detection may be inappropriate for systems with large variations in gas concentration because of absorption saturation and changing gas acoustic properties. Nevertheless, photoacoustic spectroscopy is a promising technique for the analysis of dilute mixtures in miniature chemical systems. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1489493
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