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  • 1
    Electronic Resource
    Electronic Resource
    Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2033-2040 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution measurements on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1551 (1994)] of the transport barrier in the "Enhanced Dα" (EDA) regime, which has increased particle transport without large edge localized modes, show steep density and temperature gradients over a region of 2–5 mm, with peak pressure gradients up to 12 MPa/m. Evolution of the pedestal at the L-H transition is consistent with a large, rapid drop in thermal conductivity across the barrier. A quasi-coherent fluctuation in density, potential, and Bpol, with f0∼50–150 kHz and kθ∼4 cm−1, always appears in the barrier during EDA, and drives a large particle flux. Conditions to access the steady-state EDA regime in deuterium include δ〉0.35, q95〉3.5, and L-mode target density n¯e〉1.2×1020 m−3. A reduced q95 limit is found for hydrogen discharges. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1348329
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  • 2
    Electronic Resource
    Electronic Resource
    Character formulas for irreducible modules of the Lie superalgebras sl(m/n) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 2278-2304 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Kac distinguished between typical and atypical finite-dimensional irreducible representations of the Lie superalgebras sl(m/n) and provided an explicit character formula appropriate to all the typical representations. Here, the range of validity of some character formulas for atypical representations that have been proposed are discussed. Several of them are of the Kac–Weyl type, but then it is proved that all formulas of this type fail to correctly give the character of one particular atypical representation of sl(3/4). Having ruled out, therefore, all such formulas, a completely new extension of the Kac–Weyl character formula is proposed. The validity of this formula in the case of all covariant tensor irreducible representations is proved, and some evidence in support of the conjecture that it covers all irreducible representations of sl(m/n) is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528637
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  • 3
    Electronic Resource
    Electronic Resource
    Particle transport in the scrape-off layer and its relationship to discharge density limit in Alcator C-Mod : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2107-2117 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cross-field particle transport in the scrape-off layer (SOL) of Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] can be characterized by an effective particle diffusivity (Deff) that increases markedly with distance from the separatrix. As a consequence, recycling onto the main-chamber walls is large compared to plasma flows into the divertor volume. The SOL exhibits a two-layer structure: Steep gradients and moderate fluctuation levels are typically found in a ∼5 mm region near the separatrix (near SOL) where parallel electron conduction typically dominates energy losses. Small gradients and larger fluctuation levels with longer correlation times are found outside this region (far SOL). Deff in the near SOL increases strongly with local plasma collisionality normalized to the magnetic connection length. As the discharge density limit is approached, Deff and associated fluctuation levels become large across the entire SOL and cross-field heat convection everywhere exceeds parallel conduction losses, impacting the power balance of the discharge. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352596
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of neutral particles on edge dynamics in Alcator C-Mod plasmas : 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. 1919-1926 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutral particle densities and energy losses have been measured in the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. Their effect on the formation and evolution of the edge barrier which accompanies the enhanced confinement regime are discussed. The neutrals can enter the edge dynamics through the particle, momentum, and energy balance. Neutral densities of up to 5×1016 m−3 have been measured in the edge barrier region. Neutrals enter the local dynamics around most of the periphery, not just at the X-point. High resolution measurements of the ionization profile have been obtained for the region near the separatrix. The profile shifts inside the separatrix as the plasma is making a transition from low-to high-mode confinement (H-mode) regimes, partly accounting for the dramatic rise in edge density. The measured neutral density is large enough to affect the bulk ion momentum by charge exchange, and thereby introduces a negative radial electric field at the edge. At the same time, significant edge heat flux, carried by the neutrals, contributes to the measured power loss. At very high edge densities, this loss mechanism could contribute to quenching H-modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874016
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  • 5
    Electronic Resource
    Electronic Resource
    A medium-frequency interferometer for studying auroral radio emissions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3200-3206 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An interferometer for use between 2.5 and 3.0 MHz has recently been developed for the purpose of studying auroral radio emissions. The instrument consists of an array of 17 antennas, associated electronics for amplitude and phase measurements, and computer hardware for instrument control and data recording. In its standard operational mode, the instrument sweeps from 2.5 to 3.0 MHz in 1 kHz steps every 1.5 s. The intensity of the received signal and the phase at each antenna is measured for each 1-kHz-wide bin. These data can be used to produce spectrograms showing the intensity of the received signal versus frequency and time and for determining the direction of arrival for any signal in the instrument bandwidth. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305518
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  • 6
    Electronic Resource
    Electronic Resource
    High-resolution edge Thomson scattering measurements on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1107-1110 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-resolution Thomson scattering diagnostic is in operation on the Alcator C-Mod tokamak, measuring radial profiles of electron temperature and density at the plasma edge. Photons are scattered from a Nd–yttrium–aluminum–garnet laser beam pulsed at 30 Hz (1.3 J, 8 ns pulse), and are measured by a filter polychromator with four spectral channels. The polychromator measures Te in the range of 15–800 eV and ne of 0.3–3×1020 m−3. Twenty scattering volumes are located about the last closed flux surface, spaced for a nominal resolution of 1.3 mm in midplane radial coordinates. High resolution is essential for measuring edge Te and ne profiles on C-Mod, since these quantities exhibit gradient scale lengths as small as 2 mm in H mode. The steep profiles at the H mode edge are fit to a parameterized pedestal function for ease of analysis. Measured profiles are compared with edge profiles from electron cyclotron emission and visible continuum diagnostics. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319367
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  • 7
    Electronic Resource
    Electronic Resource
    Thermal bias annealing evidence for the defect pool in amorphous silicon thin-film transistors (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1416-1418 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin-film transistors were thermally annealed while a bias voltage was applied to the gate electrode. The transfer characteristics were then measured, and the density of states distributions derived by field-effect analysis. The results indicate that the equilibrium distribution and number of defects in the transistor channel region depend on the position of the Fermi energy during annealing. Thus the density of states can be increased or decreased in parts of the band gap. A high Fermi energy during annealing results in few states high in the gap and more states low in the gap. The reverse is true for annealing while the Fermi energy is low. This is consistent with the defect pool model for silicon dangling bond states and suggests that most deep states are part of the defect pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103452
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  • 8
    Electronic Resource
    Electronic Resource
    Time and temperature dependence of instability mechanisms in amorphous silicon thin-film transistors (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1323-1325 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the time and temperature dependence of the two prominent instability mechanisms in amorphous silicon thin-film transistors, namely, the creation of metastable states in the a-Si:H and the charge trapping in the silicon nitride gate insulator. The state creation process shows a power law time dependence and is thermally activated. The charge trapping process shows a logarithmic time dependence and has a very small temperature dependence. The results for the state creation process are consistent with a model of Si dangling bond formation in the bulk a-Si:H due to weak SiSi bond breaking stabilized by diffusive hydrogen motion. The logarithmic time dependence and weak temperature dependence for the charge trapping in the nitride suggest that the charge injection from the a-Si:H to the nitride is the rate limiting step and not subsequent conduction in the nitride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100704
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  • 9
    Electronic Resource
    Electronic Resource
    Intrusions in the active layer of channeled-substrate-planar laser diodes (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1093-1096 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Channeled-substrate-planar laser diodes from various wafers were observed to develop a node or dark spot in their near-field patterns after failure during lifetesting. "Node'' devices from each wafer were angle lapped and stained in an attempt to uncover a physical mechanism for this common failure symptom. Optical microscopic examination of the beveled cross sections revealed that an intrusion, in the form of a spike at the tip of the zinc diffusion front, had penetrated into the active layer of these diodes. The node observed in the near-field pattern appears to be in a position corresponding to the location of the spike in the active region. In addition, cathodoluminescence measurements on other "node'' diodes revealed a dark line region approximately 2 μm wide running parallel to and in the middle of the 5-μm contact stripe. We believe that this dark line region is representative of an area of nonradiative recombination which occurs in the portion of the active layer containing the intrusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339740
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  • 10
    Electronic Resource
    Electronic Resource
    High resolution visible continuum imaging diagnostic on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 940-943 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high spatial resolution CCD based one-dimensional imaging system to measure visible continuum emissivity profiles from Alcator C-Mod tokamak plasmas is described. The instrument has chordal resolution that is better than 1 mm for the edge region of the plasma, where very sharp (1 to 10 mm) gradient lengths in plasma parameters are observed after the formation of the H-mode transport barrier. Each image has up to 2048 pixels, and total spatial coverage goes from 2 cm inside of the magnetic axis to ∼4 cm outside of the last closed flux surface in the ∼22 cm horizontal minor radius plasmas. Time resolution can be varied from 0.21 ms to 4 ms; good signal to noise is achieved with 1 ms integration under typical plasma conditions. The emission over most of the plasma volume is dominated by free–free bremsstrahlung, and can be used to infer local values of the average ion charge (Zeff). Toroidally localized puffing of deuterium, nitrogen, and helium reveals that a significant contribution to the signal in the scrape-off layer at the extreme edge of the plasma can come from diatomic molecular band pseudocontinuum emission. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323245
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