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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 666-668 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A conventional zero-dimensional (uniform plasma parameters with no spatial variations) fluid model will provide a good match with an experimental electron cyclotron resonance ion source (ECRIS) charge-state distribution (CSD) if provided with a judicious set of user inputs. However, this arbitrarily chosen set of inputs is not necessarily unique. To be truly predictive, an ECRIS model should rely on experimental parameters as inputs. A multi-species model for an ECRIS plasma using experimental parameters as inputs is under development. The model eliminates electron temperature as a user input by employing a 2 V(v,θ) Fokker–Planck code with an ECR heating term to calculate the non-Maxwellian anisotropic electron distribution function. Further arbitrary user inputs are eliminated in favor of controlled parameters by bounce averaging the Fokker–Planck coefficients for a one-dimensional (1D)/2 V axial model. The neutral gas modeling has been extended to 1D using axially coupled particle balance equations. The improved model is able to reproduce experimental Faraday cup (CSDA) from the Argonne National Laboratory's ECR-II. Further elimination of arbitrary inputs is expected when the ion model is extended to 1D. © 2000 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 54 (1989), S. 493-495 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs/AlGaAs semiconductor lasers with very high quality etched facets have been fabricated. Laser facets are formed by the chemically assisted ion beam etching technique with SiO2 as the etch mask. The threshold current densities of lasers produced with this technique are almost identical to comparable lasers with one etched and one cleaved facet. L-shaped lasers, which make use of total internal reflection, have also been fabricated. The threshold current density of L-shaped lasers is similar to that of rectangular lasers with comparable cavity length.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6826-6833 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interdiffusion in InGaAs/InP quantum wells has been studied using magneto-optical transmission spectroscopy. The effects of dopants in the substrates and quantum wells, overgrowth and annealing processes have been investigated, providing useful information on the interdiffusion effects in typical growth and fabrication processes. The blue shift effect which is often observed in multiple quantum well (MQW) structures subjected to heat treatment, is attributed to a dominant group V interdiffusion which can be suppressed by high defect densities in the substrate. The presence of Zn-dopants in an overgrown layer on top of the MQW structures causes a counteractive redshift effect after long annealing times due to group III diffusion, but in situ Zn- or S-dopants produce no observable shift in transition energies due to interdiffusion. This is attributed to enhanced group III interdiffusion induced by Zn diffusion into the MQWs. We conclude that there are very different interdiffusion mechanisms for group III and group V elements and support the recent suggestion of vacancy-related group V interdiffusion in contrast to the interstitialcy mechanism for the group III interdiffusion. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4294-4296 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report experimental results on monolithic stable-resonator semiconductor lasers. Curved end mirrors defining a near-concentric stable resonator were fabricated on wide-stripe GaAs/AlGaAs GRINSCH-SQW lasers using reactive-ion-etching. These lasers oscillate in close to the expected lowest-order Gaussian stable-resonator modes at threshold, evolving into a coherent superposition of higher-order modes as the pump current is increased up to two to three times threshold. At higher pump currents nonlinear defocusing effects cause the resonators to become geometrically unstable so that the lateral modes are determined by both the resonator geometry and the saturated gain and index profile. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5410-5414 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The specific volumes of Pd40Ni40P20 were measured in the liquid, glass, and crystallized states. It was found that in the molten state, for temperatures below ∼1000 K, the specific volume measurement was successful only if the specimens were properly purified. Such purification could be achieved by fluxing the molten specimen in dehydrated boron oxide. Relaxation effects are observed and they manifested themselves in the variation of the thermal expansion coefficient with the quenching rates of the glassy specimens. The intersection points of the specific volume curves of the liquid (both stable and metastable), glass and crystallized are 573±80 and 492±80 K (extrapolated values), respectively. The former agrees very well with the glass transition temperature 577 K, obtained by the calorimetry method, while the latter implies that the melt, in accord with free volume theory, will have collapsed to the glass before that temperature is reached.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2781-2788 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Argon gas puff experiments on a 3–4 MA generator show that the K-shell x-ray yield is optimized for a 2.5 cm initial diameter and 110 ns implosion time. By varying the driver current, the K-shell yield varies from 13 to 18 kJ following a current to the fourth power scaling. Comparisons of these experimental data to one-dimensional radiation-hydrodynamic simulations with and without enhanced transport coefficients show that the measured K-shell yields exceed those predicted based solely on kinetic energy input.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1091-1101 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of the beam divergence of the input pump laser beams on the nonlinear frequency mixing process in a dielectric medium is discussed. The divergent laser beams have finite angular spreads so that all of the interactions between the two input beams can never satisfy the phase-matching condition exactly. A numerical model is developed to investigate the effects of input beam divergence on conversion efficiency. The angular spread of each of the input beams is represented by a set of plane waves having a distribution of propagation directions. Each of the plane-wave components from one input beam is allowed to interact with all the plane-wave components of the second input beam. This model is applicable to processes such as sum frequency generation, difference frequency generation, and optical parametric amplification. Second-harmonic generations as a special case of sum frequency generation is used as an example in the numerical studies. Results indicate that the conversion efficiency is dependent on the amount of beam divergence, the input intensity, and the length of the nonlinear medium. These parameters must be optimized with respect to one another to maximize the conversion. The optimization is especially critical in high-power systems where high conversion efficiency is sought.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3082-3098 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The neoclassical theory of ion transport in rotating axisymmetric plasmas is formulated. The flow speed is allowed to be of the order of the ion thermal speed. It is shown that the ion distribution function becomes Maxwellian, with temperature uniform on a magnetic surface, and the poloidal flow decays, in a few transit or collision times, in general. A drift kinetic equation is derived which is a simple generalization of the drift kinetic equation for nonrotating plasmas. The radial gradient of the toroidal angular velocity appears as a driving term like the temperature gradient. Both gradients drive the transport of toroidal angular momentum and energy, in general; Onsager relations for the two-by-two transport matrix are derived. The off-diagonal transport coefficients are shown to be zero if the magnetic field has up–down symmetry. A simple expression for the enhancement of the ion thermal conductivity in the banana regime, caused by rotation, is derived. The neoclassical viscosity is shown not to be enhanced by rotation in the banana regime, and to be small in the collisionality parameter in the collisional regime, assuming up–down symmetry. In the collisional regime, the thermal conductivity is shown to be suppressed by the effects of rotation.
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sustained stabilization of the n=1 kink mode by plasma rotation at beta approaching twice the stability limit calculated without a wall has been achieved in DIII-D by a combination of error field reduction and sufficient rotation drive. Previous experiments have transiently exceeded the no-wall beta limit. However, demonstration of sustained rotational stabilization has remained elusive because the rotation has been found to decay whenever the plasma is wall stabilized. Recent theory [Boozer, Phys. Rev. Lett. 86, 5059 (2001)] predicts a resonant response to error fields in a plasma approaching marginal stability to a low-n kink mode. Enhancement of magnetic nonaxisymmetry in the plasma leads to strong damping of the toroidal rotation, precisely in the high-beta regime where it is needed for stabilization. This resonant response, or "error field amplification" is demonstrated in DIII-D experiments: applied n=1 radial fields cause enhanced plasma response and strong rotation damping at beta above the no wall limit but have little effect at lower beta. The discovery of an error field amplification has led to sustained operation above the no-wall limit through improved magnetic field symmetrization using an external coil set. The required symmetrization is determined both by optimizing the external currents with respect to the plasma rotation and by use of feedback to detect and minimize the plasma response to nonaxisymmetric fields as beta increases. Ideal stability analysis and rotation braking experiments at different beta values show that beta is maintained 50% higher than the no wall stability limit for durations greater than 1 s, and approaches beta twice the no-wall limit in several cases, with steady-state rotation levels. The results suggest that improved magnetic-field symmetry could allow plasmas to be maintained well above no-wall beta limit for as long as sufficient torque is provided. © 2002 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1706-1714 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spherically convergent ion focus (SCIF) devices relying on hot electrons to create the confining electrostatic well are found to be subject to a counterstreaming ion instability. Nonlocal linear stability theories in a spherical geometry are formulated and solved both analytically and numerically. The results of previous calculations of local linear theory are used for comparison. Linear growth rates of the order of the beam transit frequency are predicted. The consequence of these instabilities awaits a nonlinear treatment.
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