267 research outputs found

    Negative-Energy Perturbations in Circularly Cylindrical Equilibria within the Framework of Maxwell-Drift Kinetic Theory

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    The conditions for the existence of negative-energy perturbations (which could be nonlinearly unstable and cause anomalous transport) are investigated in the framework of linearized collisionless Maxwell-drift kinetic theory for the case of equilibria of magnetically confined, circularly cylindrical plasmas and vanishing initial field perturbations. For wave vectors with a non-vanishing component parallel to the magnetic field, the plane equilibrium conditions (derived by Throumoulopoulos and Pfirsch [Phys Rev. E {\bf 49}, 3290 (1994)]) are shown to remain valid, while the condition for perpendicular perturbations (which are found to be the most important modes) is modified. Consequently, besides the tokamak equilibrium regime in which the existence of negative-energy perturbations is related to the threshold value of 2/3 of the quantity ην=lnTνlnNν\eta_\nu = \frac {\partial \ln T_\nu} {\partial \ln N_\nu}, a new regime appears, not present in plane equilibria, in which negative-energy perturbations exist for {\em any} value of ην\eta_\nu. For various analytic cold-ion tokamak equilibria a substantial fraction of thermal electrons are associated with negative-energy perturbations (active particles). In particular, for linearly stable equilibria of a paramagnetic plasma with flat electron temperature profile (ηe=0\eta_e=0), the entire velocity space is occupied by active electrons. The part of the velocity space occupied by active particles increases from the center to the plasma edge and is larger in a paramagnetic plasma than in a diamagnetic plasma with the same pressure profile. It is also shown that, unlike in plane equilibria, negative-energy perturbations exist in force-free reversed-field pinch equilibria with a substantial fraction of active particles.Comment: 31 pages, late

    Negative-energy perturbations in cylindrical equilibria with a radial electric field

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    The impact of an equilibrium radial electric field EE on negative-energy perturbations (NEPs) (which are potentially dangerous because they can lead to either linear or nonlinear explosive instabilities) in cylindrical equilibria of magnetically confined plasmas is investigated within the framework of Maxwell-drift kinetic theory. It turns out that for wave vectors with a non-vanishing component parallel to the magnetic field the conditions for the existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D. Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for the existence of perpendicular NEPs, which are found to be the most important perturbations, is modified. For eiϕTi|e_i\phi|\approx T_i (ϕ\phi is the electrostatic potential) and Ti/Te>βcP/(B2/8π)T_i/T_e > \beta_c\approx P/(B^2/8\pi) (PP is the total plasma pressure), a case which is of operational interest in magnetic confinement systems, the existence of perpendicular NEPs depends on eνEe_\nu E, where eνe_\nu is the charge of the particle species ν\nu. In this case the electric field can reduce the NEPs activity in the edge region of tokamaklike and stellaratorlike equilibria with identical parabolic pressure profiles, the reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late

    Kinetic Equations for Microscopic Turbulence

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    New Formulation of Dirac's Constraint Theory

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    Complete solution of the modified cherry oscillator problem

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    Generalized cherry oscillators and negative energy waves

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    Gyrokinetic field theory

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    Negative-energy waves in a magnetized, homogeneous plasma

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    Negative-energy waves in an inhomogeneous force-free Vlasov plasma with sheared magnetic field

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    Negative-Energy Perturbations in General Axisymmetric and Helical Maxwell-Vlasov Equilibria

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