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  • 1
    Electronic Resource
    Electronic Resource
    Transitionless enhanced confinement and the role of radial electric field shear (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 615-625 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evidence is presented for the role of radial electric field shear in enhanced confinement regimes attained without sharp bifurcations or transitions. Temperature scans at constant density, created in the reheat phase following deuterium pellet injection into supershot plasmas in the Tokamak Fusion Test Reactor [J. D. Strachan, et al., Phys. Rev. Lett. 58, 1004 (1987)] are simulated using a physics-based transport model. The slow reheat of the ion temperature profile, during which the temperature nearly doubles, is not explained by relatively comprehensive models of transport due to Ion Temperature Gradient Driven Turbulence (ITGDT), which depends primarily on the (unchanging) electron density gradient. An extended model, including the suppression of toroidal ITGDT by self-consistent radial electric field shear, does reproduce the reheat phase. The extended reheat at constant density is observed in supershot but not L-Mode plasmas. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873867
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  • 2
    Electronic Resource
    Electronic Resource
    Bursting processes in plasmas and relevant nonlinear model equations (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 14-22 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Important intrinsic plasma instabilities manifest themselves in the form of periodic bursts of fluctuations rather than as a state of stationary fluctuations, which a conventional application of quasilinear theory would lead to expect. A set of coupled nonlinear equations for the time evolution of the fluctuation amplitude and of the driving factor of the relevant instability is shown to have the features necessary to reproduce the variety of bursts that are observed experimentally. These are the periodicity, the duration, and the shape of the bursts, special consideration being given to the excitation of modes by high-energy particle populations in thermalized plasmas and to a model for the transition from a bursting state to one of stationary fluctuations. A model is introduced that is relevant to the case where the spatial dependence of the mode amplitude is important. The application of the given analysis to the bursty wave emissions observed in space is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871104
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  • 3
    Electronic Resource
    Electronic Resource
    Interchange instabilities in a partially ionized plasma (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2217-2231 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a partially ionized plasma, the charged particle population is coupled to the neutrals through charge exchange, ionization and recombination. An interchange instability is identified in which the driving factor is the neutral pressure gradient and the dominant collisional process is charge exchange. Regimes are considered in which the mean free path for neutral collisions with ions λni is small in comparison to the macroscopic length scales. The instability is analogous to a gravitational interchange mode with an effective gravity geff=νinVn where νin is the collision frequency of ions with neutrals. The neutral flow Vn=−(Mniνin)−1dpn/dx results from a balance between the neutral pressure gradient and collisional friction with the ions. An arbitrary kyλni dispersion relation is derived using fluid equations to describe the ions and the Boltzmann equation to describe the neutrals. This dispersion relation contains viscous and inertial effects and is substantially altered in the presence of realistic parallel wavelength due to a coupling between the unstable interchange mode and a stabilizing shear Alfvén mode. Reasonable conditions under which the modes may exist are examined and the possible relevance to divertor plasmas is considered. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872895
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature anisotropy effect on the toroidal ion temperature gradient mode (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 152-158 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the local kinetic and fluid approaches, the effects of the anisotropies in the ion temperature and in the ion temperature gradient on the toroidal ion temperature gradient driven mode are investigated. A study of the effect of the increasing ion temperature relative to the fixed electron temperature in the peaked density limit is also made. Comparisons are given between the new toroidal results and the previous slab results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860428
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  • 5
    Electronic Resource
    Electronic Resource
    High-energy components and collective modes in thermonuclear plasmas (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 4060-4072 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theory of a class of collective modes of a thermonuclear magnetically confined plasma, with frequencies in the range of the ion-cyclotron frequency and of its harmonics, is presented. These modes can be excited by their resonant cyclotron interaction with a plasma component of relatively high-energy particles characterized by a strongly anisotropic distribution in velocity space. Normal modes that are spatially localized by the inhomogeneity of the plasma density are found. This ensures that the energy gained by their resonant interaction is not convected away. The mode spatial localization can be significantly altered by the magnetic field inhomogeneity for a given class of plasma density profiles. Special attention is devoted to the case of a spin polarized plasma, where the charged products of fusion reactions are anisotropically distributed. It is shown that for the mode of polarization that enhances nuclear reaction rates the tritium will be rapidly depolarized for toroidal configurations with relatively mild gradients of the confining magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865749
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  • 6
    Electronic Resource
    Electronic Resource
    Global modes and high-energy particles in ignited plasmas (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 927-943 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fusion-produced alpha particles may spontaneously enhance the stability of an ignited plasma against m=1 internal modes. Stable values of the poloidal beta of the thermal plasma component significantly in excess of the ideal magnetohydrodynamic threshold can be attained, provided the region where the magnetic helical parameter q is below unity is not too wide and the ignition temperature is not too high. A comprehensive analysis of the different instability regimes is presented, with special attention to so-called "fishbone oscillations'' and their influence on the ignition energy balance. The theoretical predictions compare favorably with sawtooth suppression experiments in the JET tokamak [Phys. Rev. Lett. 60, 2148 (1988)] with high-power, ion-cyclotron resonant frequency heating, where energetic ions in the MeV range are produced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859240
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  • 7
    Electronic Resource
    Electronic Resource
    Change of confinement properties and transition from absolute to non-normal mode microinstabilities (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2817-2822 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The change in confinement properties that can be induced in experiments, where the plasma is heated by an external injection system, is considered to be related to the transition from a regime where "absolute'' microinstabilities are excited at the edge of the plasma column to a regime where these microinstabilities can exist only as non-normal modes because of the effects of the local gradient of the E×B rotation frequency that is induced. Ion-temperature-gradient-driven modes are analyzed as an important example and the threshold conditions for their disappearances as normal modes are evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860155
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  • 8
    Electronic Resource
    Electronic Resource
    Symmetries and global transport equations (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2582-2590 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anomalous transport of the electron thermal energy and that of the longitudinal current density are related to each other and described by a diffusion matrix equation. The symmetry properties of the matrix diffusion coefficients are identified and used to prescribe realistic conditions on the radial profiles of the electron temperature T and of the current density J(parallel).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859970
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  • 9
    Electronic Resource
    Electronic Resource
    Macroscopic plasma oscillation bursts (fishbones) resulting from high-energy populations (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1630-1648 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oscillation bursts (fishbones) of magnetically confined plasmas are associated with the excitation of an m0=1 mode when the ideal magnetohydrodynamic (MHD) threshold for the instability of this mode is reached. Near this threshold and in the absence of an effective "viscous'' dissipative process, this mode remains marginally stable as a result of finite ion Larmor radius effects and has a real frequency of oscillation near the ion diamagnetic frequency. The release of the mode excitation energy related to the gradient of the plasma pressure, in the case of perpendicular neutral beam injection, is allowed by the resonant interaction of the mode with fast trapped ions that precess around the torus as a result of the curvature and the gradient of the confining magnetic field. This process plays the role of an effective viscosity. A consequence of the presented interpretation is that fishbone oscillations may also be excited in the case of parallel beam injection. In fact, for relatively low values of the beam transverse pressure, the basic mode frequency is related to the parameters of the target plasma and does not depend on the magnetic drift frequency of the beam particles that are injected nor on their velocity distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866702
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  • 10
    Electronic Resource
    Electronic Resource
    Candidate mode for electron thermal energy transport in multi-keV plasmas (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2322-2333 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear and quasilinear theory of the collisionless trapped electron mode (also called the "ubiquitous'' mode) is analyzed, in order to illustrate its possible role in the electron thermal energy transport observed in magnetically confined plasmas. This instability is driven by the combined effects of the plasma pressure gradient (which includes the contributions from the temperature gradients of ions and electrons) and of the local magnetic curvature drift of trapped electrons and of circulating and trapped ions. Depending on the value of its wavelength across the magnetic field, this mode can connect with a branch of the ion temperature gradient instability, provided the ion temperature gradient is sufficiently strong. Also, under certain conditions, it can be driven unstable solely by a combination of electron temperature gradient and Landau damping by trapped electrons. The relevant modes are found to be robust against variation of parameters such as the electron collisionality, and to be consistent candidates in order to explain the experimentally observed rate of electron thermal energy transport from the center of the plasma column.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859497
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