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  • 1
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    Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta) (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-05-15
    Description: For the first time, nonlinear gyrokinetic simulations of I-mode plasmas are performed and compared with experiment. I-mode is a high confinement regime, featuring energy confinement similar to H-mode, but without enhanced particle and impurity particle confinement [D. G. Whyte et al. , Nucl. Fusion 50 , 105005 (2010)]. As a consequence of the separation between heat and particle transport, I-mode exhibits several favorable characteristics compared to H-mode. The nonlinear gyrokinetic code GYRO [J. Candy and R. E. Waltz, J Comput. Phys. 186 , 545 (2003)] is used to explore the effects of E × B shear and profile stiffness in I-mode and compare with L-mode. The nonlinear GYRO simulations show that I-mode core ion temperature and electron temperature profiles are more stiff than L-mode core plasmas. Scans of the input E × B shear in GYRO simulations show that E × B shearing of turbulence is a stronger effect in the core of I-mode than L-mode. The nonlinear simulations match the observed reductions in long wavelength density fluctuation levels across the L-I transition but underestimate the reduction of long wavelength electron temperature fluctuation levels. The comparisons between experiment and gyrokinetic simulations for I-mode suggest that increased E × B shearing of turbulence combined with increased profile stiffness are responsible for the reductions in core turbulence observed in the experiment, and that I-mode resembles H-mode plasmas more than L-mode plasmas with regards to marginal stability and temperature profile stiffness.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Alternative optical concept for electron cyclotron emission imaginga) (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-07-01
    Description: The implementation of advanced electron cyclotron emission imaging (ECEI) systems on tokamak experiments has revolutionized the diagnosis of magnetohydrodynamic (MHD) activities and improved our understanding of instabilities, which lead to disruptions. It is therefore desirable to have an ECEI system on the ITER tokamak. However, the large size of optical components in presently used ECEI systems have, up to now, precluded the implementation of an ECEI system on ITER. This paper describes a new optical ECEI concept that employs a single spherical mirror as the only optical component and exploits the astigmatism of such a mirror to produce an image with one-dimensional spatial resolution on the detector. Since this alternative approach would only require a thin slit as the viewing port to the plasma, it would make the implementation of an ECEI system on ITER feasible. The results obtained from proof-of-principle experiments with a 125 GHz microwave system are presented.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
    Electronic Resource
    Electronic Resource
    Electrical resistivity, magnetization, and grain-boundary precipitate in nickel-rich nickel-indium alloys : 35th annual conference on magentism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5361-5363 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The variations of the electrical resistivity, the magnetization, and the grain-boundary precipitates of a Ni-rich Ni-In alloy system with In concentration up to 7.5 at. % have been investigated as functions of annealing time at 773 K. For samples homogenized at 1225 K, clear grain boundaries are observed. However, for these aged samples, we observed both grain-boundary precipitates and variations of the electrical resistivity and the magnetization; and the binary alloy with higher In concentration has the higher variation rate in the decrease of the electrical resistivity, the increase of the magnetization, and the growth of the grain-boundary precipitates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348029
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  • 4
    Electronic Resource
    Electronic Resource
    Basic circuits for inductive-energy pulsed power systems (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4333-4337 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive analysis of pulse formation in inductive-energy pulsed power circuits is presented. The output waveforms, with relevant circuit parameters, are derived for four basic systems, including two new circuit configurations useful for practical applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344950
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  • 5
    Electronic Resource
    Electronic Resource
    Inert gas clusters of C6F+6: The evolution from isolated ion to solid matrix (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3297-3309 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Simultaneous laser-induced fluorescence (LIF) spectra and time-of-flight mass spectra have been recorded for ionic clusters, C6F+6⋅Rn where R=He, Ne, and Ar. These spectra span the regime of clusters extending from the isolated ion to the ion located in the corresponding inert-gas matrix (except He). The conclusions of these studies include the following. Abundant clusters with n=1 and 2 exist in symmetrical forms with one atom above and below the benzene plane. Such configurations appear, however, to be evolutionary dead ends with respect to the ultimate matrix structure. Rather, the latter likely corresponds to several inert-gas atoms sharing more or less equally the cationic charge on each side of the ring. From our results, it may be speculated that most of the essential features of the matrix LIF spectra are obtained with the completion of what is roughly the first solvent shell in the cluster, 6–10 atoms, depending upon the inert gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457889
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  • 6
    Electronic Resource
    Electronic Resource
    A simple and efficient external gas filtration and trapping system for excimer lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2464-2469 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Excimer lasers are excellent sources of coherent light in the ultraviolet range of the spectrum. However, they have the drawback of requiring significant maintenance due to the corrosive gases, generation of dust, and contamination of the laser chamber optics which occur during normal operation. Improvements which are generally applicable to any excimer laser system are specifically described in terms of the two Questek (Lambda Physik, Acton, MA) model 2860 lasers in our lab. The same basic procedures are currently being implemented in two Lambda lasers in other research groups at our university. A novel gas triple filtration system, a simple cold trap with a counter-flow heat exchanger, and a careful selection of valves have been added to minimize dust contamination of the optics, to decrease contamination and leakage of the gas fill, to provide safe and easy dust removal, and to reduce maintenance downtime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145227
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of power gain in an inductive energy pulsed power system with an optically controlled semiconductor opening switch (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2330-2332 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Power gain has been observed, for the first time, in an inductive energy storage pulsed power system with an optically controlled semiconductor opening switch. A specially tailored 1.054 μm pulse from a Nd:glass laser was utilized to activate a GaAs switch of the p-i-n diode configuration, producing an output pulse with a power gain of more than 10.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103884
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  • 8
    Electronic Resource
    Electronic Resource
    The variation of microstructure in Czochralski silicon induced by low-high two step anneal (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 56-59 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Systematic low-high two-step and high-low-high three-step annealing studies were conducted to investigate the microdefects generated in Czochralski silicon wafers. It was found that cluster precipitates entangled with dislocations are annihilated during extended low temperature anneal. A model involving the recombination of vacancies with interstitials is proposed to explain this phenomenon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366701
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of oxygen precipitates on silicon resistivity in the 650 °C range (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2817-2821 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new kinetic model is proposed to explain the resistivity shift phenomenon at annealing temperatures of around 550–800 °C. In this model, thermal donor generation and acceptor annihilation both contribute to the resistivity shift, but the latter contributes most. The rodlike defect which can only grow at temperatures below 800 °C is speculated to act as a gettering center for the acceptors. This model is used to explain the most salient features of "new donor'' activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337873
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  • 10
    Electronic Resource
    Electronic Resource
    Oxygen precipitation retardation and recovery phenomena in Czochralski silicon: Experimental observations, nuclei dissolution model, and relevancy with nucleation issues (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 917-931 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report experimental results of an oxygen precipitation study carried out using Czochralski silicon wafers. A two-step anneal scheme was employed: a lower-temperature step (at 650 or 750 °C for 0–128 h) for SiO2 precipitate nucleation and a higher temperature step (at 1050 °C for 0–64 h) for growth. The oxygen precipitation rate is monitored by measuring the interstitial oxygen (Oi) concentration in the silicon lattice. We have found that (i) a precipitation retardation phenomenon exists for wafers that received prolonged nucleation annealing treatment (from 2 to 16 h), and (ii) this retardation phenomenon gives way to a precipitation recovery phenomenon for wafers that received still longer nucleation annealing treatment (for 8–128 h). We also describe a nuclei dissolution model to explain the retardation/recovery phenomena. The dissolution proceeds against an Oi supersaturation which would normally drive the nuclei into growth.The most important aspects of the model are (i) the dissolution occurs at the onset of the high-temperature growth anneal step, (ii) the factor directly opposing the Oi supersaturation and leading to the nuclei dissolution process is attributed to a large supersaturation of silicon self-interstitials (I supersaturation), essentially also generated at the onset of the growth anneal step, (iii) the generation of the I supersaturation is associated with a nuclei/precipitate polymorph change again occurring at the onset of the growth anneal step. The fundamental physical cause leading to these phenomena is the exigent-accommodation volume (or exigent volume) associated with precipitate growth. This model can explain the present results and is consistent with many other experimental results. We then examine the relevance of the exigent-volume factor with nucleation issues such as its effect on ramping, the effect of carbon, the existence of multiple polymorphs of SiO2, multiple nucleation paths, and a nucleation incubation phenomenon. We believe contributions of the exigent-volume factor to the nucleation phenomena generally exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336564
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