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  • 1
    Publication Date: 2016-06-21
    Description: Recent DIII-D experiments have increased the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Improved understanding of scenario stability has led to the achievement of very high values of β p and β N , despite strong internal transport barriers. Good confinement has been achieved with reduced toroidal rotation. These high β p plasmas challenge the energy transport understanding, especially in the electron energy channel. A new turbulent transport model, named TGLF-SAT1, has been developed which improves the transport prediction. Experiments extending results to long pulse on EAST, based on the physics basis developed at DIII-D, have been conducted. More investigations will be carried out on EAST with more additional auxiliary power to come online in the near term.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 2
    Publication Date: 2014-12-13
    Description: The dependence of divertor asymmetry and scrape-off layer (SOL) flow on heating power has been investigated in the Experimental Advanced Superconducting Tokamak (EAST). Divertor plasma exhibits an outboard-enhanced in-out asymmetry in heat flux in lower single null configuration for in reversed (ion ∇ B drift direction toward the upper X-point) field directions. Upper single null exhibits an inboard-favored asymmetry in low heating power condition, while exhibits an outboard-favored asymmetry when increasing the heating power. Double null has the strongest in-out asymmetry in heat flux, favoring the outer divertor. The in-out asymmetry ratios of q t , out / q t , in and P out / P total increase with the power across the separatrix P loss , which is probably induced by the enhanced radial particle transport due to a large pressure gradient. The characteristics of the measured SOL parallel flow under various discharge conditions are consistent with the Pfirsch-Schlüter (PS) flow with the parallel Mach number M ∥ decreasing with the line averaged density but increasing with P loss , in the same direction as the PS flow. The contributions of both poloidal E × B drift and parallel flow on poloidal particle transport in SOL on EAST are also assessed.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 3
    Publication Date: 2014-09-24
    Description: High-confinement regime with high-frequency and low-energy-loss small edge localized modes (ELMs) was achieved in Experimental Advanced Superconducting Tokamak by using the lower hybrid current drive and ion cyclotron resonance heating with lithium wall conditioning. The small ELMs are usually accompanied with a quasi-coherent mode at frequency around 30 kHz, as detected by the Langmuir probes near the separatrix. The coherent mode, with weak magnetic perturbations different from the precursor of conventional ELMs, propagates in the electron diamagnetic drift direction in the lab frame with the poloidal wavelength λ θ  ∼ 14 cm, corresponding to both high poloidal and toroidal mode numbers (m 〉 60 and n 〉 12). This coherent mode, carrying high-temperature high-density filament-like plasma, drives considerable transport from the pedestal region into the scrape-off layer towards divertor region. The co-existence of small ELMs and quasi-coherent modes is beneficial for the sustainment of long pulse H-mode regime without significant confinement degradation.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 4
    Publication Date: 2014-06-19
    Description: An ion cyclotron range of frequencies (ICRF) system with power up to 6.0 MW and a lower hybrid current drive (LHCD) system up to 4 MW have been applied for heating and current drive experiments in Experimental Advanced Superconducting Tokomak (EAST). Significant progress has been made with ICRF heating and LHCD for realizing the H-mode plasma operation in EAST. During 2010 and 2012 experimental campaigns, ICRF heating experiments were carried out at the fixed frequency of 27MHz, achieving effective ions and electrons heating with the H minority heating (H-MH) mode. The H-MH mode produced good plasma performance, and realized H-mode using ICRF power alone in 2012. In 2010, H-modes were generated and sustained by LHCD alone, where lithium coating and gas puffing near the mouth of the LH launcher were applied to improve the LHCD power coupling and penetration into the core plasmas of H-modes. In 2012, the combination of LHCD and ICRH power extended the H-mode duration up to over 30 s. H-modes with various types of edge localized modes (ELMs) have been achieved with H IPB98 (y, 2) ranging from 0.7 to over unity. A brief overview of LHCD and ICRF Heating experiment and their application in achieving H-mode operation during these two campaigns will be presented.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 5
    Publication Date: 2016-09-29
    Description: An alternating integrator has been designed for the Experimental Advanced Superconducting Tokamak that is intended for long pulse operation of up to 1000 s. The electromagnetic operating environment for the device is so complex that it could affect the performance of the integrator. The new integrator system is carefully designed and actualized based on specific reduced electromagnetic interference requirements, which were formulated based on consideration of processing of the input signals, the isolation properties, and the circuit board layout and grounding. The developed integrator shows excellent electromagnetic compatibility and low-drift properties.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2886-2891 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ceramic coatings of zirconium nitride have been fabricated on nickel, silicon, and M2 high-speed steel by methods of reactive magnetron sputtering ion plating (RMSP) and the dynamic ion mixing (DIM). The microhardness values of ZrN film prepared by RMSP with different nitrogen partial pressure have been discussed. The scratch tests provide that the adhesion of ZrN film produced by dynamic ion mixing is better than that by reactive magnetron sputtering ion plating. Auger electron spectroscopy analysis is used to analyze the composition distribution of ZrN film prepared by DIM and indicates that there is a transitional layer between the ZrN film and substrate. Meanwhile, by cross-sectional and the plan-view transmission electron microscopy, it is observed that the interlayer of amorphous structure exists in the interface zone between ZrN film and substrate. According to the analysis of energy-dispersive x-ray analysis patterns, the composition of this amorphous region fabricated by RMSP is Ni51Zr49 (≈NiZr), as is that fabricated by DIM. (Up to now it has not been reported that the amorphous transitional layer occurs in reactive magnetron sputtering ion plating). The reason why the adhesion of coating by DIM is better than that by RMSP is not the formation of the transitional layer in ion-beam-assisted deposition but the particle bombardment effects on the bulk of the thin film.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 6167-6171 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silver contact pads to c-axis-oriented thin films of YBa2Cu3O7 (YBCO) were defined using three different techniques: (1) deposition through stencil masks; (2) liftoff; and (3) Ar plasma etching of in situ deposited Ag. A specific contact resistance of ρc(77 K) = 1 × 10−7 Ω cm2 was found for the in situ deposited contacts. Contacts defined with stencil masks and liftoff showed a ρc(77 K) ∼ 10−5 and ∼ 10−2 Ω cm2, respectively. Core-level photoelectron spectroscopy measurements indicate that the resist and acetone applied to the YBCO thin film during patterning do not introduce surface impurity phases in addition to those formed upon air exposure. Distinct chemical shifts originating from process-induced surface impurity phases were observed in photoelectron spectra taken on films prepared for contact definition by liftoff, i.e., exposed to the lithographic developer and deionized water. These findings correlate with the measured increase in contact resistance. Cross-sectional transmission electron microscopy images of an in situ deposited Ag contact unveil a 20–30-A(ring)-thick interface layer, in which the 12 A(ring) periodicity along the YBCO c axis vanishes. The presence of this layer could explain the absence of Josephson effects in YBCO/noble-metal/low-Tc superconductor junctions where the currents are forced to flow perpendicular to the a-b planes.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3306-3309 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Iron-silicide has been formed by ion implantation of iron into silicon (111). In the as-implanted sample, a new type of orthorhombic FeSi2 phase was found. Although the lattice parameters of the new phase are the same as those of the known semiconductor β-FeSi2, its point group and space group were different and determined to be mmm and Pbca, respectively. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 836-838 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7−δ (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 A(ring) thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 498-500 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interface atomic structure of in situ sputter deposited silver contacts to a- and c-axis oriented thin films of YBa2Cu3O7 (YBCO) was investigated with cross-section transmission electron microscopy (TEM). A structurally disordered interface layer, approximately 25 A(ring) thick, was found for Ag contacts to c-axis oriented films. Electron diffraction analysis provides clear evidence for loss of the 11.7 A(ring) lattice periodicity along the YBCO c-axis in this zone. No such disordered interface layer could be identified in TEM images of Ag contacts to a-axis oriented films. These findings may have important bearing on fabrication of high Tc proximity coupled superconductor/normal metal/superconductor Josephson devices.
    Type of Medium: Electronic Resource
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