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  • 1
    Electronic Resource
    Electronic Resource
    Description of turbulent transport in tokamaks by invariants (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2907-2919 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In general, turbulent transport drives a plasma toward a state of turbulent equipartition, in which Lagrangian invariants are uniformly distributed. Different invariants decay with different rates, and in tokamaks the frozen-in law of particles in the poloidal magnetic field survives longer than the corresponding law for the toroidal field, assuming that the trapped particles dominate the turbulent transport. Therefore, the plasma profiles depend on the safety factor q(r), and the condition for convection of trapped particles is that the shear dq/dr is positive. There are two ways to suppress this convection and thereby enhance confinement. The first one is to reverse the magnetic shear. The energy of typical trapped particles then increases outward instead of inward, which suppresses instabilities. The second method is to eliminate the trapped ions by poloidal rotation, and thereby create a transport barrier. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872422
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  • 2
    Electronic Resource
    Electronic Resource
    Three-dimensional stability of drift vortices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 160-167 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The three-dimensional stability of drift vortices that are two-dimensionally stable in the framework of the Hasegawa–Mima equation is studied. The three-dimensionality is caused by a coupling of the vortex to ion-acoustic waves that propagate along the magnetic field. It is concluded that this coupling does not significantly destabilize the vortex. A general stability criterion is derived that guarantees stability if the ratio between the parallel wave number k and the azimuthal mode number m is large enough. It is also found that no instability exists in the limit k→0 if the potential vorticity is a strictly decreasing function of r. Such profiles are typical for vortices that are two-dimensionally stable. Some particular profiles where the potential vorticity vanishes outside some radius are also examined. In one case an instability with m=1 is found, but a numerical solution of the eigenvalue problem shows that the maximum growth rate is very small, three orders of magnitude smaller than the angular velocity of the vortex flow. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871842
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  • 3
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Three-dimensional stability of drift vortices' '' [Phys. Plasmas 3, 160 (1996)] (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4292-4292 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The three-dimensional stability of drift vortices is studied in the framework of the Hasegawa-Mima equation. The coupling of the vortex to ion-acoustic waves along the magnetic fields causes the three-dimensionality. It is concluded that this coupling does not significantly destabilize the vortex. (AIP) © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871563
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  • 4
    Electronic Resource
    Electronic Resource
    Anomalous pinch flux in tokamaks driven by the longitudinal adiabatic invariant (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2874-2876 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The turbulent particle flux in tokamaks has an inward component, the pinch flux, which is independent of the density gradient. It is proposed that this flux represents a tendency of the particle distribution to approach turbulent equipartition, which means that the phase space density is constant on hypersurfaces defined by those invariants that are not destroyed by the turbulence. For tokamaks the two first adiabatic invariants give the peaked density profile n∼1/q of trapped particles. Sharp gradients are predicted near the separatrix of divertor plasmas. The physical mechanism of the pinch is as follows. When a parcel of trapped particles is displaced inward by the turbulent fluctuations, their parallel velocity must increase in order to keep the longitudinal invariant J constant. This is equivalent to adiabatic compression, and increases the density. The turbulence is assumed to be caused by thermally driven electrostatic modes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871186
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of nonstationary dipole vortices (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 622-629 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of tilted dipole vortices in the equivalent barotropic vorticity (or Hasegawa–Mima) equation is studied. A recent theory is compared with numerical simulations and found to describe the short time behavior of dipole vortices well. In the long time limit the dipoles are found to either disintegrate or relax toward a steady eastward propagating dipole vortex. This relaxation is a consequence of nonviscous enstrophy loss by the dipole vortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858648
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  • 6
    Electronic Resource
    Electronic Resource
    The existence of stationary vortex solutions of the equations for nonlinear drift waves in plasmas and nonlinear Rossby waves (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1788-1796 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of including the electron temperature gradient and higher-order terms in the expansion of the density profile in the equations for nonlinear drift waves in plasmas is studied, as well as the effect of expanding the equation for nonlinear Rossby waves to higher orders in the amplitude. The two cases are very similar, and earlier studies have concluded that these effects would make a new kind of stationary monopole vortex solution possible. This solution would have a unique functional form in the whole plane, and for some parameter values no closed streamlines. It is shown that this conclusion is correct, and that such solutions do not exist. It is also pointed out that these additional effects become particularly important in the region of very long wavelengths, where they give rise to wave breaking and a transfer of energy toward shorter wavelengths. This can prevent the condensation to zonal flows that has been predicted earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858909
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic vortices in nonuniform plasmas (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1367-1370 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A localized generation of magnetic fields is found to occur in an unmagnetized nonuniform plasma. The process is described in terms of dipole and monopole vortex solutions of the equations governing the electron motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866251
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  • 8
    Electronic Resource
    Electronic Resource
    Motion of dipole vortices in a weakly inhomogeneous medium and related convective transport (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2042-2047 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general equation of motion describing the propagation of dipole vortices in a weakly inhomogeneous medium is derived. The solution of this equation agrees well with previously published numerical simulations. The contribution of dipole vortices to passive transport in the direction of the external inhomogeneity is then estimated. Since they can make large, oscillatory excursions in this direction (in contrast to monopole vortices), their contribution can be quite significant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859425
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  • 9
    Electronic Resource
    Electronic Resource
    Global vortex pattern in a rotating plasma (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2097-2100 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of nonlinear fluid equations that include the effect of finite ion Larmor radius is derived to describe the dynamics of flute modes in a rotating inhomogeneous plasma with a strong axial magnetic field. It is shown that these equations possess a solution in the form of a global pattern of two-dimensional vortices, different from the solitary vortex structure found earlier for the nonlinear Rossby waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866144
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  • 10
    Electronic Resource
    Electronic Resource
    Propagation of discontinuities in the Hasegawa–Mima equation (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1585-1587 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of curves with discontinuous third derivatives of the potential in a fluid described by the Hasegawa–Mima equation is studied. It is shown that the area inside a closed curve of this kind is conserved, and a law governing the evolution of the magnitude of the discontinuity is derived. The hypothesis that such curves carry soliton properties is put forward.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866517
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