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1.
Summary The radial evolution of Alfvénic correlation is such that its value decreases with increasing heliocentric distance. So far
this behaviour has been interpreted as an increase in the local production of ?inward? modes interacting destructively with
the ?outward? modes. This work, which deals with largescale turbulence, shows that local generation phenomena are not commonly
found in the solar wind and that the Alfvénic character of the fluctuations mainly depend on the ?outward? modes alone. The
interaction of these modes with density and/or magnetic-field structures convected by the wind causes their destruction and
a consequent depletion of the Alfvénic correlation. The same effect would be obtained if ?inward? modes were really present.
Our conclusions are that large-scale ?inward? modes are the spectral counterpart of non-propagating field and plasma structures
convected by the solar wind and identified as both compression regions and pressure balance structures.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
2.
The higher-order, low-amplitude inertial Alfvén wave (IAW) dressed soliton and chaos are investigated in a magnetized plasma. In the linear limit, the dispersion relation for propagation of IAWs in plasmas is also obtained in the presence of electron thermal effects and illustrated numerically. It is found that the electron inertial length plays an important role for wave dispersion effects and its phase speed is increased on including the electron temperature in the model. The reductive perturbation method is employed to obtain the first-order IAW Korteweg–de Vries (KdV) soliton and second-order dressed soliton solutions analytically, which gives electron density dip (or rarefactive) structure and moves with super Alfvénic speed in plasmas. The numerical illustrations of the KdV and dressed IAW solitons are also presented by using the laboratory and space plasma parameters given in the literature. Furthermore, a numerical study of quasi-periodicity and chaotic behaviour of IAWs in the presence of external periodic force is also discussed in detail. The effects of plasma beta (which depends on plasma density, electron temperature, and magnetic field intensity) and obliqueness of the wave propagation on the formation of nonlinear Alfvénic wave structures have also been presented. 相似文献
3.
T. M. Mishonov M. V. Stoev Y. G. Maneva 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):533-536
Absorption of Alfvén waves is considered to be the main mechanism of
heating in the solar corona. It is concluded that the sharp increase
of the plasma temperature by two orders of magnitude is related to a
self-induced opacity with respect to Alfvén waves. The maximal
frequency for propagation of Alfvén waves is determined by the
strongly temperature dependent kinematic viscosity. In such a way
the temperature jump is due to absorption of high frequency Alfvén
waves in a narrow layer above the solar surface. It is calculated
the power per unit area dissipated in this layer due to damping of
Alfvén waves that blows up the plasma and gives birth to the
solar wind. A model short wave-length (WKB) evaluation takes into
account the 1/f2 frequency dependence of the transversal magnetic
field and velocity spectral densities. Such spectral densities agree
with old magnetometric data taken by Voyager 1 and recent
theoretical calculations in the framework of Langevin-Burgers MHD.
The presented theory predicts existence of intensive high frequency
MHD Alfvén waves in the cold layer beneath the corona. It is
briefly discussed how this statement can be checked experimentally.
It is demonstrated that the magnitude of the Alfvén waves
generating random noise and the solar wind velocity can be expressed
only in terms of satellite experimental data. It is advocated that
investigation of properties of the solar surface as a random driver by
optical methods is an important task for future solar physics. 相似文献
4.
We have investigated the propagation of Alfvén waves in bismuth at 4.2 K using a microwave interferometer at 34.45 GHz and
applying magnetic fields up to 1 Tesla. At certain angles between the external magnetic field and the direction of propagation
of the Alfvén waves in the crystal, we have observed intense oscillations of the amplitude and the phase of the interferometer
curves. We explain these oscillations as due to a superposition of the two Alfvén wave modes. The phase velocities of the
two modes are calculated from the measurements. Comparing them with a general dispersion relation we find good agreement between
the theoretical phase velocities and the experimental values. 相似文献
5.
Ion pickup by a monochromatic low-frequency Alfvén wave, which
propagates along the background magnetic field, has recently been
investigated in a low beta plasma (Lu and Li 2007 Phys.
Plasmas 14 042303). In this paper, the monochromatic Alfvén
wave is generalized to a spectrum of Alfvén waves with random
phase. It finds that the process of ion pickup can be divided into
two stages. First, ions are picked up in the transverse direction,
and then phase difference (randomization) between ions due to their
different parallel thermal motions leads to heating of the ions. The
heating is dominant in the direction perpendicular to the background
magnetic field. The temperatures of the ions at the asymptotic stage do
not depend on individual waves in the spectrum, but are determined
by the total amplitude of the waves. The effect of the initial ion
bulk flow in the parallel direction on the heating is also
considered in this paper. 相似文献
6.
The conservation of magnetic flux in the evolution and collapse of massive stars suggests that Alfvén magnetoplasma oscillations
can be excited in an isolated neutron star by residual (after the supernova explosion) disturbances of the magnetized electron-nuclear
plasma localized in the peripheral crust of the star. The frequencies of the poloidal Alfvén oscillations are calculated in
the uniform magnetic field approximation, and it is found that the periods of the oscillations fall into the time interval
of the periodicity of radio pulsar radiation. This coincidence of the periods could mean that, at least for some pulsars observed
in the radio range, the electromagnetic activity is due to converstion of the energy of magnetoplasma oscillations into electromagnetic
radiation.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 593–598 (10 November 1996) 相似文献
7.
Discrete Alfvn eigenmodes in international thermonuclear experimental reactor operations with negative magnetic shear 下载免费PDF全文
Discrete Alfvn eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes are trapped by the α-induced potential wells along the magnetic field line. Here α =-q2Rdβ/dr with q being the safety factor, β the ratio between plasma and magnetic pressures, and R the major radius, and r the minor radius. Due to negligible continuum damping via wave energy tunneling, these Alfvn eigenmodes could be readily destabilized by energetic particles. 相似文献
8.
The modulation of Alfvén waves interacting with a non-uniform and non-stationary plasma is considered. The waveforms are allowed to change rapidly. We examine our phenomena by means of exact analytical solutions of the MHD equations in the presence of large amplitude disturbances of the magnetic field and plasma density. In contrast to the WKB approach, we do not have to use limiting assumptions regarding the variations of the background medium. We show that the large amplitude time and space disturbances lead to a new cut-off frequency for Alfvén wave propagation. A rapid reshaping of the Alfvén waveform can also obstruct the resonant interactions between the waves and the plasma particles. 相似文献
9.
It is shown that the curvature of magnetic field lines may enhance the rate of energy absorption of surface quasimodes by a few orders of magnitude at the Alfvén resonance surfaces located well into the plasma interior. 相似文献
10.
ABSTRACT The propagation of magnetoacoustic (fast magnetohydrodynamic) waves in pair-ion (PI) fullerene plasma is studied in the linear and nonlinear regimes. The pair-ion (PI) fullerene plasma is theorized as homogeneous, magnetized, warm and collisionless. Employing multi-fluid magnetohydrodynamic model, the dispersion relation is obtained and wave dispersion effects which appear through ion inertial length are discussed. Using reductive perturbation technique (RPT), the Korteweg–de Vries (KdV) equation is derived and its solution for small but finite amplitude magnetoacoustic solitons propagating in the direction perpendicular to the external magnetic field is presented. The compressive magnetoacoustic soliton (i.e. positive potential pulse) propagating with super Alfvénic speed is obtained in magnetized PI fullerene plasma. The variations in the amplitude and width of the magnetoacoustic soliton structures are also illustrated by using numerical values of the plasma parameters such as ions' density, temperature difference between fullerene ions and magnetic field intensity, which have been taken from the PI plasma experiments already published in the literature. 相似文献