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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and properties of high-Tc YBa2Cu3O7−y oriented thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3493-3497 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The a- and c-axis-oriented YBa2Cu3O7−y thin films were prepared by rf magnetron sputtering technique. The characterization of the thin films was carried out by inductively coupled plasma atomic emission spectroscopy, x-ray diffraction, and scanning Auger profile techniques. The Tc, Tc(H), Jc(H), and Hc2 -T(near Tc) were measured by the standard dc four-probe method. It was found that very strong anisotropy of this material was manifested in its superconducting properties, especially for c-axis-oriented thin films. It was also found that Jc depends very strongly upon stoichiometric composition 123, preferential orientation of the film, and the characteristic of the film-substrate interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346360
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  • 2
    Electronic Resource
    Electronic Resource
    Thermally activated dissipation and critical field Hc2 in c-oriented high-Tc Bi-Pb-Sr-Ca-Cu-O thin film (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4379-4383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of resistivity-temperature (R-T) curves measured under various applied fields in a high-Tc Bi-Pb-Sr-Ca-Cu-O thin film which has a zero-resistance temperature Tc0 of 110 K is reported. The remarkable broadening of the transition width is discussed under the flux-creep model, considering the very short coherence length of this oxide superconductor. The resistivity is thermally activated, which is consistent with the Arrhenius law with a magnetic field and orientation-dependent activation energy U0(H,aitch-theta). The U0(H,aitch-theta) has a very high value of 381.6 meV under a field of 0.1 T parallel to the c axis. The upper critical field Hc2 determined from these R-T curves shows high values and the effect of flux creep to the Hc2(0) is examined by the irreversible behavior with the "giant'' flux-creep model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348362
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  • 3
    Electronic Resource
    Electronic Resource
    Critical current and flux pinning near Tc of a YBa2Cu3O7 thin film (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2461-2463 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The voltage V versus current I of a high-quality YBa2Cu3O7−x thin film with zero-resistance temperature equal to 90.8 K was measured at temperatures near Tc (85, 87, and 90 K, respectively) under different magnetic fields (0–7 T). A significant result is that the critical-current density of the film reached 1.37×104 A/cm2 (zero field) even at 90 K, implying that strong pinning centers exist in our sample. However, a small applied magnetic field will diminish the critical-current densities remarkably. The pinning-force densities are found to follow Kramer's scaling law in both perpendicular and parallel directions of the magnetic fields to the c axis of the film. A possible influence of thermally activated flux creep on the pinning mechanism is confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349400
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  • 4
    Electronic Resource
    Electronic Resource
    Critical current measurements in YBa2Cu3O7−x thin film grown on LaAlO3 substrate (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 884-886 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current density Jc(B,T) of epitaxial YBa2Cu3O7−x (YBCO) thin films on LaAlO3 was measured under different applied magnetic fields (0–7 T) with the temperature ranging from 65 to 79 K. At 65 K, the zero-field critical current density of the best film was 5.8×106 A/cm2; even at magnetic fields up to 7 T, Jc could reach as high as 1×106 A/cm2. Strong anisotropy was observed at 79 K. The anisotropy behavior diminished with the decrease of temperature. Experimental results showed that Jc was proportional to (Tc−T)3/2 ; this was in accordance with the theoretical explanation by the Josephson junction model for granular superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346784
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  • 5
    Electronic Resource
    Electronic Resource
    Studies of instability and transport in sheared-slab plasmas with very weak magnetic shear (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3334-3340 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using kinetic theory, for tokamak plasmas with very weak (positive or negative) magnetic shear (VWS). The gradient of magnetic shear as well as the effects of parallel and perpendicular velocity shear (v(parallel)′ and vE′) are included in the defining equations. Two eigenmodes: the double (D) and the global (G) are found to coexist. Parametric dependence of these instabilities, and of the corresponding quasilinear transport is systematically analyzed. It is shown that, in VWS plasmas, a parallel velocity shear (PVS) may stabilize or destabilize the modes, depending on the individual as well as the relative signs of PVS and of the gradient of magnetic shear. The quasilinear transport induced by the instabilities may be significantly reduced with PVS in VWS plasmas. The vE′ values required to completely suppress the instabilities are much lower in VWS plasmas than they are in normal plasmas. Possible correlations with tokamak experiments are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872474
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  • 6
    Electronic Resource
    Electronic Resource
    Reynolds stress of localized toroidal modes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4236-4245 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation of the two-dimensional (2-D) toroidal eigenmode problem reveals the possibility of a new consistent 2-D structure, the dissipative ballooning mode of the second kind (BM-II). In contrast to the conventional ballooning mode, the new mode is poloidally localized at π/2 (or−π/2), and possesses significant radial asymmetry. The radial asymmetry, in turn, allows the dissipative BM-II to generate considerably larger Reynolds stress as compared to the standard slab drift-type modes. It is also shown that a wide class of localized dissipative toroidal modes are likely to be of the dissipative BM-II nature, suggesting that at the tokamak edge, the fluctuation generated Reynolds stress (a possible source of poloidal flow) can be significant. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871048
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  • 7
    Electronic Resource
    Electronic Resource
    MHD magnetic fluctuation measurements using a heavy ion beam probe : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3061-3063 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a technique for measuring magnetic fluctuations using a heavy ion beam probe (HIBP) and presents the results of the first experiment to measure locally the internal magnetic structure of MHD modes in a hot, tokamak plasma. In these experiments on the TEXT tokamak, the toroidal position of the HIBP beam at the detector is used to measure the toroidal component of the magnetic vector potential fluctuations, A˜φ, at a localized position in the plasma. In an axisymmetric system a purely local measurement is possible. However, the detection method employed and the asymmetries in the tokamak introduce path effects. The importance of the path effects is estimated through numerical simulations of the experiment, and it is found that in this experiment the path effects are small throughout much of the plasma. In addition, toroidal asymmetries reduce the signal amplitude, but do not greatly distort the radial profile. The accuracy of the numerical simulations and detection technique is tested in a plasma with a known A˜φ, with agreement obtained to within 5%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141727
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  • 8
    Electronic Resource
    Electronic Resource
    Study of microinstabilities in toroidal plasmas with negative magnetic shear (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3065-3072 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microinstabilities driven by a parallel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyrokinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower and the threshold temperature gradient ηicr is higher for plasmas with negative magnetic shear compared to plasmas with positive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insignificant, does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871654
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  • 9
    Electronic Resource
    Electronic Resource
    Transition to high mode induced by reduction of magnetic stress (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3243-3245 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transition to the high mode (H mode) of plasma operation in tokamaks and stellarators can be triggered by reduction of the magnetic stress. The magnetic stress can be reduced directly, by stabilization of the magnetic perturbation, or by increasing the plasma density and ion temperature if all of the other parameters are fixed. This implies the existence of thresholds in density and ion temperature. The theory is applied to a class of H-mode phenomena observed experimentally. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871155
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  • 10
    Electronic Resource
    Electronic Resource
    Continuum damping of ideal toroidal Alfvén eigenmodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 381-389 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A perturbation theory based on the two-dimensional (2-D) ballooning transform is systematically developed for ideal toroidal Alfvén eigenmodes (TAEs). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are compared with previous calculations. It is found that in some narrow intervals of the parameter mεˆ, the damping rate varies very rapidly. These regions correspond precisely to the root missing intervals of the numerical solution by Rosenbluth et al. [Phys. Fluids B 4, 2189 (1992)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870839
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