16 research outputs found
On linear coupling of acoustic and cyclotron waves in plasma flows
It is found that in magnetized electrostatic plasma flows the velocity shear
couples ion-acoustic waves with ion-cyclotron waves and leads, under favorable
conditions, to their efficient reciprocal transformations. It is shown that in
a two-dimensional setup this coupling has a remarkable feature: it is governed
by equations that are exactly similar to the ones describing coupling of sound
waves with internal gravity waves [Rogava & Mahajan: Phys. Rev. E vol.55, 1185
(1997)] in neutral fluid flows. Using another noteworthy quantum mechanical
analogy we calculate transformation coefficients and give fully analytic,
quantitative description of the coupling efficiency for flows with low shearing
rates.Comment: 5 pages, no figures. Submitted to "Physics of Plasmas
On over-reflection and generation of Gravito-Alfven waves in solar-type stars
The dynamics of linear perturbations is studied in magnetized plasma shear
flows with a constant shearing rate and with gravity-induced stratification.
The general set of linearized equations is derived and the two-dimensional case
is considered in detail. The Boussinesq approximation is used in order to
examine relatively small-scale perturbations of low-frequency modes:
Gravito-Alfven waves (GAW) and Entropy Mode (EM) perturbations. It is shown
that for flows with arbitrary shearing rate there exists a finite time interval
of non-adiabatic evolution of the perturbations. The non-adiabatic behavior
manifests itself in a twofold way, viz. by the over-reflection of the GAWs and
by the generation of GAWs from EM perturbations. It is shown that these
phenomena act as efficient transformers of the equilibrium flow energy into the
energy of the perturbations for moderate and high shearing rate solar plasma
flows. Efficient generation of GAW by EM takes place for shearing rates about
an order of magnitude smaller than necessary for development of a shear
instability. The latter fact could have important consequences for the problem
of angular momentum redistribution within the Sun and solar-type stars.Comment: 20 pages (preprint format), 4 figures; to appear in The Astrophysical
Journal (August 1, 2007, v664, N2 issue
The Lagrangian frequency spectrum as a diagnostic for magnetohydrodynamic turbulence dynamics
For the phenomenological description of magnetohydrodynamic turbulence
competing models exist, e.g. Boldyrev [Phys.Rev.Lett. \textbf{96}, 115002,
2006] and Gogoberidze [Phys.Plas. \textbf{14}, 022304, 2007], which predict the
same Eulerian inertial-range scaling of the turbulent energy spectrum although
they employ fundamentally different basic interaction mechanisms. {A relation
is found that links} the Lagrangian frequency spectrum {with} the
autocorrelation timescale of the turbulent fluctuations, ,
and the associated cascade timescale, . Thus, the
Lagrangian energy spectrum can serve to identify weak
() and strong
() interaction mechanisms providing
insight into the turbulent energy cascade. The new approach is illustrated by
results from direct numerical simulations of two- and three-dimensional
incompressible MHD turbulence.Comment: accepted for publication in PR
Scaling law of the plasma turbulence with non conservative fluxes
It is shown that in the presence of anisotropic kinetic dissipation existence
of scale invariant power law spectrum of plasma turbulence is possible.
Obtained scale invariant spectrum is not associated with the constant flux of
any physical quantity. Application of the model to the high frequency part of
the solar wind turbulence is discussed.Comment: Phys Rev E, accepte
Gravitational Radiation from Primordial Helical MHD Turbulence
We consider gravitational waves (GWs) generated by primordial inverse-cascade
helical magneto-hydrodynamical (MHD) turbulence produced by bubble collisions
at the electroweak phase transitions (EWPT). Compared to the unmagnetized EWPT
case, the spectrum of MHD-turbulence-generated GWs peaks at lower frequency
with larger amplitude and can be detected by the proposed Laser Interferometer
Space Antenna (LISA).Comment: 4 pages, 1 figure, references and discussions added, figure modified,
results unchanged, Phys. Rev. Lett. accepte
Quantifying shear-induced wave transformations in the solar wind
The possibility of velocity shear-induced linear transformations of different
magnetohydrodynamic waves in the solar wind is studied both analytically and
numerically. A quantitative analysis of the wave transformation processes for
all possible plasma- regimes is performed. By applying the obtained
criteria for effective wave coupling to the solar wind parameters, we show that
velocity shear-induced linear transformations of Alfv\'en waves into
magneto-acoustic waves could effectively take place for the relatively
low-frequency Alfv\'en waves in the energy containing interval. The obtained
results are in a good qualitative agreement with the observed features of
density perturbations in the solar wind.Comment: Astrophysical Journal (accepted
Gamma Ray Burst Constraints on Ultraviolet Lorentz Invariance Violation
We present a unified general formalism for ultraviolet Lorentz invariance
violation (LV) testing through electromagnetic wave propagation, based on both
dispersion and rotation measure data. This allows for a direct comparison of
the efficacy of different data to constrain LV. As an example we study the
signature of LV on the rotation of the polarization plane of -rays from
gamma ray bursts in a LV model. Here -ray polarization data can provide
a strong constraint on LV, 13 orders of magnitude more restrictive than a
potential constraint from the rotation of the cosmic microwave background
polarization proposed by Gamboa, L\'{o}pez-Sarri\'{o}n, and Polychronakos
(2006).Comment: 5 pages, references added, accepted for publication in Phys. Lett.