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  • 21
    Electronic Resource
    Electronic Resource
    Two novel applications of bootstrap currents: Snakes and jitter stabilization (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3252-3260 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both neoclassical theory and certain turbulence theories of particle transport in tokamaks predict the existence of bootstrap (i.e., pressure-driven) currents. Two new applications of this form of noninductive current are considered in this work. In the first, an earlier model of the nonlinearly saturated m=1 tearing mode is extended to include the stabilizing effect of a bootstrap current inside the island. This is used to explain several observed features of the so-called "snake'' reported in the Joint European Torus (JET) [R. D. Gill, A. W. Edwards, D. Pasini, and A. Weller, Nucl. Fusion 32, 723 (1992)]. The second application involves an alternating current (ac) form of bootstrap current, produced by pressure-gradient fluctuations. It is suggested that a time-dependent (in the plasma frame), radio-frequency (rf) power source can be used to produce localized pressure fluctuations of suitable frequency and amplitude to implement the dynamic stabilization method for suppressing gross modes in tokamaks suggested in a recent paper [A. Thyagaraja, R. D. Hazeltine, and A. Y. Aydemir, Phys. Fluids B 4, 2733 (1992)]. This method works by "detuning'' the resonant layer by rapid current/shear fluctuations. Estimates made for the power source requirements both for small machines such as COMPASS and for larger machines like JET suggest that the method could be practically feasible. This "jitter'' (i.e., dynamic) stabilization method could provide a useful form of active instability control to avoid both gross/disruptive and fine-scale/transportive instabilities, which may set severe operating/safety constraints in the reactor regime. The results are also capable, in principle, of throwing considerable light on the local properties of current generation and diffusion in tokamaks, which may be enhanced by turbulence, as has been suggested recently by several researchers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860661
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  • 22
    Electronic Resource
    Electronic Resource
    Asymptotic theory of the nonlinearly saturated m=1 mode in tokamaks with q0〈1 (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 580-593 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the necessary and sufficient conditions required for the existence of a nonlinearly saturated m=1 tearing mode in tokamaks with q0〈1 are considered in cylindrical tokamak ordering using the asymptotic techniques developed by one of the authors in an earlier paper [Phys. Fluids 24, 1716 (1981)]. The outer equations for the helical perturbation amplitude ψ1(r) are solved exactly, in closed form for an arbitrary mean profile ψ0(r) in leading order. This is shown to result in a "no disturbance'' theorem: the m=1 perturbation must be confined to within the radius ri such that q(ri)=1. The bifurcation relation for the nondimensional perturbation amplitude is then constructed by solving the nonlinear inner critical layer equations using an ordered iterative technique. For monotonically increasing q profiles, the equation has a solution if and only if the toroidal current density of the unperturbed equilibrium has a maximum within ri and the parameter d log q(r)/[d log η(r)] [where η(r) is the resistivity profile consistent with the q profile of the unperturbed equilibrium] is sufficiently small at ri. The considerations are extended to nonmonotonic profiles as well. When the conditions are met, a nonlinearly saturated m=1 tearing mode is shown to exist with a novel island structure, quite different from those obtained from the usual Δ' analysis, which is shown to be inappropriate to the present problem. The relevance of the results of the present theory to sawtooth phenomena reported in JET [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. 1, p. 377] and other tokamaks is briefly discussed. The solution constitutes an analytically solved test case for numerical simulation codes to leading orders in a/R and the shear parameter d log q/d log η.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859856
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  • 23
    Electronic Resource
    Electronic Resource
    Proposal for measuring magnetic fluctuations in tokamaks by Thomson scattering (abstract) : Eighth topical conference on high—temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3072-3072 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Thomson scattering is proposed for the direct measurement of magnetic field fluctuations in a tokamak. The analysis is based on the electron fluid equations. The ordering λ(very-much-less-than)λturb(very-much-less-than)a, where λ and λturb are the incident and turbulence wavelengths, respectively, and a is the torus minor radius, is suggested by spectral information from observations on the TEXT tokamak, as well as general theoretical arguments. With this ordering, temperature effects are unimportant and an expression is derived for probe radiation-induced plasma polarization that depends upon density and magnetic fluctuations only. By choosing the incident probe beam to have its plane of polarization parallel to the local mean magnetic field B0, and observing the scattered power in the plane of polarization perpendicular to B0, it is shown that contributions from density fluctuations are automatically excluded. Faraday rotation is shown to have negligible influence on the scattered signal, which is accordingly determined by magnetic field fluctuations alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141734
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  • 24
    Electronic Resource
    Electronic Resource
    Investigation of the electron fluid equations in a hydrodynamic model of the negative ion source : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2720-2722 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The "hydrodynamic model'' developed by Haas, Holmes, and Lea has been extended to include all elastic collision processes between the species. The properties of the electron momentum equations are investigated in detail; the solution of these equations revealing a critical point along the source axis at which the electron drift velocity reverses direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142834
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  • 25
    Electronic Resource
    Electronic Resource
    Proposal for measuring magnetic fluctuations in tokamaks by Thomson scattering (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3540-3543 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Thomson scattering is proposed for the direct measurement of magnetic field fluctuations in a tokamak. The analysis is based on the electron fluid equations. The ordering λ(very-much-less-than)λturb(very-much-less-than)a, where λ and λturb are the incident and turbulence wavelengths, respectively, and a is the torus minor radius, is suggested by spectral information from observations on the TEXT tokamak, as well as general theoretical arguments. With this ordering, temperature effects are unimportant and an expression is derived for probe radiation-induced plasma polarization that depends upon density and magnetic fluctuations only. By choosing the incident probe beam to have its plane of polarization parallel to the local mean magnetic field B0, and observing the scattered power in the plane of polarization perpendicular to B0, it is shown that contributions from density fluctuations are automatically excluded. Faraday rotation is shown to have negligible influence on the scattered signal, which is accordingly determined by magnetic field fluctuations alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141566
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  • 26
    Electronic Resource
    Electronic Resource
    Tailoring of electron energy distributions in low-pressure inductive discharges (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 338-340 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Assuming a background Maxwellian electron distribution, the effects of adding an energetic tail upon the electron temperature and density in an inductive low-pressure argon discharge are investigated theoretically. The principal effect of the tail is to modify the rate constants for ionization, excitation, and momentum transfer. Using particle and energy conservation, the possibility of suppressing the electron temperature and increasing the electron density is demonstrated. It is found that under typical conditions of operation the electron temperature can be decreased from 2.5 to 1.5 eV, and the electron density increased by at least a factor of 2.4. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123064
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  • 27
    Electronic Resource
    Electronic Resource
    Generalized analysis of the use of induction loop probes in azimuthally symmetric inductively coupled plasma sources (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3612-3614 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using B-dot probes Meyer et al. [J. Appl. Phys. 79, 1298 (1996)] have described a method for calculating the azimuthal current, electric field, plasma permittivity, and electron density in a planar inductively coupled plasma source. They assume the phases associated with the time rate of change of the radial and axial field components to be the same. Furthermore, they restrict their analysis to the situation where the phase is independent of radius. We demonstrate that the phases for the two field directions are different. The subsequent modified forms for the plasma properties considered by Meyer et al. are presented. We also show that their procedure can be extended to cover phases which are an arbitrary function of position, and for completeness, give forms for the generalized plasma properties. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365680
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  • 28
    Electronic Resource
    Electronic Resource
    Comparison of two-hexameric hemocyanin structures from chelocerata and crustacea at sub-domain resolution
    Amsterdam : Elsevier
    Ultramicroscopy 31 (1989), S. 466 
    Details
    ISSN: 0304-3991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0304-3991(89)90368-9
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  • 29
    Electronic Resource
    Electronic Resource
    Comparative electron microscopy and image analysis of oxy- and deoxy-hemocyanin from the spiny lobster Panulirus interruptus
    Amsterdam : Elsevier
    Ultramicroscopy 49 (1993), S. 426-435 
    Details
    ISSN: 0304-3991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0304-3991(93)90248-V
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  • 30
    Electronic Resource
    Electronic Resource
    The beam emittance of negative ion sources
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 287 (1990), S. 173-175 
    Details
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0168-9002(90)91791-9
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