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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The lower hybrid current drive (LHCD) system is an important system in superconducting steady state tokamak (SST-1). It is used to drive and maintain the plasma current for 1000 s with a duty cycle of 17%. The LHCD system is being designed to launch 1 MW of radio frequency (rf) power at 3.7 GHz. The rf source is comprised of two high power klystron amplifiers, each capable of delivering 500 kW rf power. In this article, the results obtained during installation and commissioning of these klystrons are presented. Two klystrons (model TH2103D) have been successfully installed and commissioned on dummy loads, delivering ∼200 kW power for more than 1000 s. The maximum output power that could be obtained is limited due to the available direct current (dc) power supply. The test system is comprised of a TH2103D klystron, a low power rf (3.7 GHz/25 W) source, two high power four port circulators, two high power dual directional couplers, two arc detector systems, and two dummy water loads. To avoid rf breakdown in the rf components of the transmission line, the system has been pressurized with dry air to 3 bar. To energize and operate the klystron, a high voltage dc power supply, a magnet power supply, an ion pump power supply, a −65 kV floating anode modulator power supply, and a filament power supply are used. An arc detector unit has been installed to detect and initiate action within a few microseconds to protect the klystron, waveguides, and other rf passive components during arcing. To protect the klystron in the event of an arc, a fast responding (〈10 μs), rail gap based pressurized crowbar unit has been used. The entire system is water cooled to avoid excess temperature rise during high power continuous wave operation of the klystron and other rf components. The tube requires initial conditioning. Thereafter, the output rf power is studied as a function of beam parameters such as cathode voltage and beam current. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1706-1708 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical model to compute thermal stresses in passivated metal interconnects is proposed in this article. Typical aspect ratio of passivated metal interconnects is 1 or less (frequently between 0.5 and 1). Previous Eshelby-based analytical model by Niwa et al. [J. Appl. Phys. 68, 328 (1990)] is not very accurate as it fails to take into account the proximity of the interconnect to the free surface of the passivation. A recently proposed model by Wikström et al. [J. Appl. Phys. 86, 6088 (1999)] precisely does not work when the aspect ratio 〈 1. The analytical model proposed in this letter can predict stresses (average and spatial variations) in passivated metal interconnects with superior accuracy. The effect of free surface of passivation is fully taken into account and comparisons with previous works are presented. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1466-1468 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A multigap pseudospark device filled with hydrogen or argon gas is operated up to 20 kV and ejected ion beam characteristics are experimentally investigated. The ion beam of peak current density in excess of ∼500 A/cm2 and pulse duration ∼50 ns is extracted at repetitive frequency of several tens of Hz. Results of the scaling study for the ion beam current with breakdown voltage, external capacitance, and number of insulator gaps are presented.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1273-1275 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of morphology of InAs islands on Si grown through Stranski–Krastanow mode is investigated by atomic force microscopy. Formation of islands in the range of 15–50 nm is observed for depositions at various temperatures for the same monolayer coverage. Growth temperatures between 400 and 425 °C are found to yield dense ensembles of islands with uniform dimensional distributions. Found to exhibit long-term stability, these islands undergo morphological transformation when annealed at temperatures above 700 °C. Ostwald ripening occurs in these islands through an enhanced surface diffusion mechanism at high annealing temperatures. The results of annealing experiments indicate surface diffusion being the dominant mechanism responsible for morphological changes in these island structures rather than the heterointerface diffusion. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2203-2209 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The study of the Rayleigh–Taylor (RT) instability of two superposed conducting fluids acted upon by a uniform horizontal magnetic field is discussed. The usual magnetohydrodynamic (MHD) equations, with modifications to include the effect of finite Larmor radius corrections (FLR) and rotation, are taken for the description of the problem. The fluid is assumed to be dusty, and dust in the form of suspended particles is considered. The equations of the problem are linearized, and using necessary boundary conditions, a general dispersion relation for the RT instability of two superposed plasma is obtained. The dispersion relation shows no contribution of the magnetic field on the condition of the RT instability. It is also found that rotation, FLR, and suspended particles do not affect the condition of the RT instability. The different special cases are discussed to find the effect of different parameters on the growth and condition of the RT instability. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 625-634 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Kelvin–Helmholtz (K-H) instability of two fluids of a plasma, streaming in opposite directions with the same velocity and in the presence of an external magnetic field, is investigated. The external magnetic field in both fluids are in different directions. The usual magnetohydrodynamic (MHD) equations with anisotropic pressures are considered. The generalized pressure relation is used and two equations of state for two pressures are taken up in the problem. The equations are linearized and initially two different flow velocities are taken for the system. The problem is solved and a dispersion relation is obtained. It is found that the instability condition for the static configuration depends on the polytropic index of the pressure relations. The condition of instability is further obtained for MHD and Chew–Goldberger–Low (CGL) systems. For the nonstatic streaming configuration it is also found that growth rate of K-H instability depends on various polytropic indices and magnetic field. © 1998 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4180-4182 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The simple binary compound, MgB2, has created enormous excitement, due to its remarkably high Tc (39 K), its exotic electronic and phononic structure, as well as its potential technological application. However, contrary to the initial expectation, worldwide efforts to enhance the Tc of this material by means of chemical doping and applying hydrostatic pressure have failed. Investigations of other diborides or related materials have also resulted in finding of lower Tc's. In this letter we report a slight, but significant enhancement of Tc in MgB2 films grown on boron crystals, which may stem from tensile-type strain. This finding opens up a new possibility for further optimizing Tc in MgB2 and perhaps in related materials. © 2001 American Institute of Physics.
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