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  • 1
    Electronic Resource
    Electronic Resource
    Improved instrument for medium energy electron diffraction and microscopy of surfaces (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1215-1219 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The REMEDIE system for reflection electron microscopy and electron diffraction at intermediate energies (0.5–20 keV) has been rebuilt with an improved imaging resolution of better than 10 nm, a convenient and versatile system for observation diffraction patterns and provision for specimen preparation and treatment suitable for surface structural studies. The current capabilities of the instrument are illustrated by results obtained from cleaved and annealed silicon (111) surfaces with or without thin deposited silver and gold layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1137978
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of the local Al concentration in AlxGa1−xAs-GaAs quantum well structures using the (200) diffraction intensity obtained with a 10 A(ring) electron beam (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1454-1456 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method for determining the local concentration of Al in the AlxGa1−xAs layer of AlxGa1−xAs-GaAs multiple quantum well structures is reported. By scanning a 10 A(ring) electron beam across the interface, the (200) dark-field scanning transmission electron microscopy (STEM) image shows the contrast of the AlxGa1−xAs-GaAs multilayer since the intensity of the (200) diffraction is sensitive to the Al concentration. The line scan intensity profile of the (200) diffraction, along a uniform specimen region of known thickness, shows the intensity variation of the (200) diffraction and reflects the local content of Al in each region. The simulation of the nanodiffraction patterns produces a chart of the (200) diffraction intensity versus the Al concentration for the determination of the local change of the Al concentration. A molecular beam epitaxy grown AlxGa1−xAs-GaAs specimen (x=0.57 as determined from Raman spectroscopy) is tested and the dark-field STEM studies show two thin layers of x=0.46 at the 1/3 and 2/3 height level within every AlxGa1−xAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100695
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  • 3
    Electronic Resource
    Electronic Resource
    Tearing modes in toroidal geometry (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 577-590 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The separation of the cylindrical tearing mode stability problem into a resistive resonant layer calculation and an external marginal ideal magnetohydrodynamic (MHD) calculation (Δ' calculation) is generalized to axisymmetric toroidal geometry. The general structure of this separation is analyzed and the marginal ideal MHD information (the toroidal generalization of Δ') required to discuss stability is isolated. This can then, in principle, be combined with relevant resonant layer calculations to determine tearing mode growth rates in realistic situations. Two examples are given: the first is an analytic treatment of toroidally coupled (m=1, n=1) and (m=2, n=1) tearing modes in a large aspect ratio torus; the second, a numerical treatment of the toroidal coupling of three tearing modes through finite pressure effects in a large aspect ratio torus. In addition, the use of a coupling integral approach for determining the stability of coupled tearing modes is discussed. Finally, the possibility of using initial value resistive MHD codes in realistic toroidal geometry to determine the necessary information from the ideal MHD marginal solution is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866840
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  • 4
    Electronic Resource
    Electronic Resource
    The stability of solutions of the classical unsteady boundary-layer equation (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 441-443 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An aspect of the stability of boundary-layer profiles containing a point of zero shear away from the wall is examined. Analysis of a viscous critical layer at the point of zero shear shows that the classical unsteady boundary-layer equation contains a short-wavelength unstable solution. The presence of this instability has consequences for the numerical solution of the classical boundary-layer equation, and may be connected with the initiation process of Van Dommelen and Shen's nonlinear unsteady separation singularity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865105
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  • 5
    Electronic Resource
    Electronic Resource
    Electron diamagnetism and toroidal coupling of tearing modes (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 426-428 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a simple model for the layer of the tearing mode, it is demonstrated that toroidally coupled tearing modes with two rational surfaces are most unstable when the ω*'s of the electrons at the rational surfaces are equal. The onset of instability may then occur because of the tuning of ω* rather than the passage of Δ'-like quantities through zero. This mechanism for the onset of instability is sharp since the resonance is narrow. The effect of toroidal rotation is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.867019
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  • 6
    Electronic Resource
    Electronic Resource
    High-energy components and collective modes in thermonuclear plasmas (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 4060-4072 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theory of a class of collective modes of a thermonuclear magnetically confined plasma, with frequencies in the range of the ion-cyclotron frequency and of its harmonics, is presented. These modes can be excited by their resonant cyclotron interaction with a plasma component of relatively high-energy particles characterized by a strongly anisotropic distribution in velocity space. Normal modes that are spatially localized by the inhomogeneity of the plasma density are found. This ensures that the energy gained by their resonant interaction is not convected away. The mode spatial localization can be significantly altered by the magnetic field inhomogeneity for a given class of plasma density profiles. Special attention is devoted to the case of a spin polarized plasma, where the charged products of fusion reactions are anisotropically distributed. It is shown that for the mode of polarization that enhances nuclear reaction rates the tritium will be rapidly depolarized for toroidal configurations with relatively mild gradients of the confining magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865749
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  • 7
    Electronic Resource
    Electronic Resource
    Toroidal effects on m=2 feedback (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 2194-2200 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal calculations on m=2 magnetic feedback are presented. These calculations are performed using a coupled Δ' formulation and show that the feedback can have a pronounced effect on the sideband (m=1 and 3) content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859033
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  • 8
    Electronic Resource
    Electronic Resource
    Linear stability of tearing modes (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3230-3244 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper examines the stability of tearing modes in a sheared slab when the width of the tearing layer is much smaller than the ion Larmor radius. The ion response is nonlocal, and the quasineutrality retains its full integral form. An expansion procedure is introduced to solve the quasineutrality equation in powers of the width of the tearing layer over the ion Larmor radius. The expansion procedure is applied to the collisionless and semicollisional tearing modes. It is found that first-order terms in the expansion are strongly stabilizing. The physics of the mode and of the stabilization are discussed. Tearing modes are observed in experiments even though the slab theory predicts stability. It is proposed that these modes grow from an equilibrium with islands at the rational surfaces. If the equilibrium islands are wider than the ion Larmor radius, the mode is unstable when Δ' is positive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865841
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  • 9
    Electronic Resource
    Electronic Resource
    A kinetic equation for spin-polarized plasmas (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 430-441 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The usual kinetic description of a plasma is extended to include variables to describe the nuclear spin. The distribution function, over phase space and the new spin variables, provides a sufficient description of a spin-polarized plasma. The evolution for the distribution function is given. The equations derived are used to calculate depolarization caused by four processes: inhomogeneous fields, collisions, collisions in inhomogeneous fields, and waves. It is found that depolarization by field inhomogeneity on scales large compared with the gyroradius is totally negligible. The same is true for collisional depolarization. Collisions in inhomogeneous fields yield a depolarization rate of order 10−3 sec−1 for deuterons and a negligible rate for tritons in a typical fusion reactor design. This is still sufficiently small on reactor time scales. However, small-amplitude magnetic fluctuations (of order 1 G) resonant with the spin precession frequency can lead to significant depolarization (depolarizes triton in 10 sec and deuteron in 100 sec).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865726
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic excitations in Fe-doped Mn3Si (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3403-3405 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inelastic scattering of neutrons has been used to study the magnetic excitations in Fe-doped Mn3Si at 7 K. Mn3Si is an incommensurate antiferromagnet with magnetic Bragg points of the form (h,k,l)±(δ,δ,δ) with δ=0.425. Its magnetic excitations are qualitatively similar to those of the γ-Mn alloys, or of the itinerant antiferromagnet, chromium. The addition of 5 at. % of iron causes the value of δ to change to 1/2, so that the material becomes a commensurate antiferromagnet, greatly simplifying the shape of the excitation spectrum. In addition the low Néel temperature (23 K) permits measurements to be extended to energies of several times kTN. Constant energy scans through a magnetic Bragg point are qualitatively consistent with the spin-wave dispersion relation forming a "cone'' around the magnetic Bragg point. Low-energy scans (1 meV≤ΔE≤4 meV) are centered on the Bragg point and flat-topped, while at higher energies (5 meV≤ΔE≤15 meV) the peak is clearly resolved as double. A fit using a damped-harmonic oscillator cross section suggests that the slope of the dispersion relation increases with energy, and that the excitations are highly damped.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338761
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