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Existence Of The Magnetorotational Instability
By posing and solving a global axisymmetric eigenvalue problem on an infinite domain with modes vanishing at zero and infinity for a differentially rotating MHD plasma, the conditions for the occurrence of a purely growing low-frequency mode known as the magnetorotational instability (MRI) are mapped. It is shown that the MRI criterion drawn from the "local dispersion relation" is at best inadequate and may even be misleading. The physics of the MRI is rather nuanced. It is dictated by the details of the radial profile of the rotation velocity Omega(r) and not just by the sign and the magnitude of its gradient, Omega'. The salient features of the class of profiles for which the MRI-like eigenmodes may occur are given along with the eigenspectrum. For a variety of other profiles, it is shown that an unstable magnetorotational mode is not a valid eigensolution.Institute for Fusion Studie
Weak and strong regimes of incompressible magnetohydrodynamic turbulence
It is shown that in the framework of the weak turbulence theory, the
autocorrelation and cascade timescales are always of the same order of
magnitude. This means that, contrary to the general belief, any model of
turbulence which implies a large number of collisions among wave packets for an
efficient energy cascade (such as the Iroshnikov-Kraichnan model) are not
compatible with the weak turbulence theory.Comment: Accepted to Phys. Plasma
Acceleration of Plasma Flows Due to Reverse Dynamo Mechanism
The "reverse-dynamo" mechanism - the amplification/generation of fast plasma
flows by micro scale (turbulent) magnetic fields via magneto-fluid coupling is
recognized and explored. It is shown that macro-scale magnetic fields and flows
are generated simultaneously and proportionately from micro scale fields and
flows. The stronger the micro-scale driver, the stronger are the macro-scale
products. Stellar and astrophysical applications are suggested.Comment: 16 pages including 3 figures. The Astrophys. J. (accepted);
additional material is given for clarification; terminology is change
Asymmetry-Driven Structure Formation in Pair Plasmas
The nonlinear propagation of electromagnetic waves in pair plasmas, in which
the electrostatic potential plays a very important but subdominant role of a
"binding glue" is investigated. Several mechanisms for structure formation are
investigated, in particular, the "asymmetry" in the initial temperatures of the
constituent species. It is shown that the temperature asymmetry leads to a
(localizing) nonlinearity that is new and qualitatively different from the ones
originating in ambient mass or density difference. The temperature asymmetry
driven focusing-defocusing nonlinearity supports stable localized wave
structures in 1-3 dimensions, which, for certain parameters, may have flat-top
shapes.Comment: 23 pages, 6 figures, introduction revised, edited typos, accepted for
publication in Phys. Rev.
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