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  • American Institute of Physics (AIP)  (3)
  • 2010-2014
  • 2000-2004  (3)
  • 2000  (3)
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  • 2010-2014
  • 2000-2004  (3)
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  • 1
    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
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3108-3112 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a very good force resolution for tuning fork based shear force microscopy as used for feedback regulation in scanning near-field optical microcopy (NSOM). The sensitivity and dynamics of fiber tips attached to 100 kHz tuning forks are investigated both experimentally and theoretically applying a finite element analysis. Operating the tuning fork at vibration amplitudes smaller than 10 nm allows to discriminate between viscous damping due to capillary wetting, and fiber bending upon tip-sample approach to hydrophilic sample surfaces indicating the direct transition from "noncontact operation" (pure viscous damping due to contamination layer) down to tip-sample contact. Viscous damping manifests in frequency shifts of less than 50 mHz, as deduced from resonance curves recorded under feedback control. For relative amplitude changes of less than 0.5% the viscous damping force acting lateral on the fiber tip is calculated to ∼100 pN using the finite element method. This detection limit proves that tuning fork based shear force control is superior to other feedback mechanisms employed in NSOM. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3034-3036 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a technique for the controlled removal of organic adsorbates from the GaAs (100) surface incorporating hydrogen dosing (atomic or molecular) combined with low-energy electron irradiation. High-resolution electron energy-loss and Auger electron spectroscopes verify a considerable desorption of carbon/hydrocarbons following electron irradiation at 50 eV under a hydrogen atom flux even at room temperature. At a sample temperature of 500 °C, static secondary ion mass spectroscopy data demonstrate selective area removal of carbon from the surface following 25 eV electron irradiation in a molecular hydrogen ambient, with a desorption rate controlled by the incident electron flux. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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