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1.
Nonlinear cylindrical fast magnetoacoustic waves are investigated in a dissipative magnetoplasma comprising of electrons,
positrons, and ions. In this regard, cylindrical Kadomtsev-Petviashvili-Burgers (CKPB) equation is derived using the small
amplitude perturbation expansion method. Furthermore, cylindrical Burgers-Kadomtsev-Petviashvili (Cyl Burgers-KP) for a fast
magnetoacoustic wave is derived, for the first time, for spatial scales larger than the electron/positron skin depths, c/ω
p(e,p). Using the tangent hyperbolic method, the solutions of both planar KPB and Burgers-KP equations are obtained and then subsequently
used as an initial profile to solve their respective counterparts in the cylindrical geometry. The effect of positron concentration,
kinematic viscosity, and plasma β are explored both for the KPB and the Burgers-KP shock waves and the differences between the two are highlighted. The temporal
evolution of the cylindrical fast magnetoacoustic wave is also numerically investigated. The present study may be beneficial
to study the propagation characteristics of nonlinear electromagnetic shock waves in planetary magnetospheres. 相似文献
2.
Obliquely propagating nonlinear structures in dense dissipative electron positron ion magnetoplasmas
Nonlinear electrostatic waves in dense dissipative magnetized electron-positron-ion (e-p-i) plasmas are investigated employing
the quantum hydrodynamic model. In this regard, Zakharov Kuznetsov Burgers (ZKB) equation is derived in dense plasmas using
the small amplitude perturbation expansion method. It is observed that obliqueness, positron concentration, kinematic viscosity,
and the ambient magnetic field significantly alter the structure of nonlinear quantum ion acoustic waves in dense dissipative
e-p-i magnetoplasmas. The present study may be useful to understand the nonlinear propagation characteristics of electrostatic
shock structures in dense astrophysical systems where the quantum effects are expected to dominate. 相似文献
3.
Prasanta Chatterjee Deb Kumar Ghosh Biswajit Sahu 《Astrophysics and Space Science》2012,339(2):261-267
The nonlinear propagation of ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of nonthermal
electrons, nonthermal positrons, and singly charged adiabatically hot positive ions, whose dynamics is governed by the two
dimensional nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation. The shock solution of the KPB equations is obtained numerically.
The effects of several parameters and ion kinematic viscosities on the properties of ion acoustic shock waves are discussed
in planar and nonplanar geometry. It is shown that the ion acoustic shock wave propagating in cylindrical/spherical geometry
with transverse perturbation will be deformed as time goes on. Also, it is seen that the strength and the steepness of the
IASWs increases with increasing β, the nonthermal parameter. 相似文献
4.
The Kadomtsev-Petviashvili-Burgers (KPB) equation is derived for coupled drift acoustic shock waves in a partially ionized non-uniform pair-ion-electron (PIE) plasma in the presence of both density and temperature gradients respectively. Both linear and nonlinear studies are presented. The nonlinear KPB equation is derived in the small amplitude approximation method and its solution is found using the tanh method. The numerical calculations also presented for PIE plasmas of fullerene plasma for illustration keeping in view the recent experiments. The effect of density and temperature inhomogeneities on the nature of the shock is also highlighted. The role of the velocity of the nonlinear structure with regard to the density and temperature gradients driven drift velocities is also pointed out and the effect of ion-neutral collision frequency is also investigated. This work may be useful for future laboratory experimental investigations on pair-ion-electron plasmas. 相似文献
5.
Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars. 相似文献
6.
Cylindrical Korteweg-de Vries-Burgers (cKdVB) equation for magnetoacoustic wave is derived for dissipative magneto plasmas. Two fluid collisionless electromagnetic model is considered and reductive perturbation method is employed to study the propagation of magnetoacoustic shock waves in cylindrical geometry. Two level finite difference method is employed by using Runge-Kutta method to solve cKdVB equation numerically. The effects of nonplanar geometry, plasma density, magnetic field strength, temperature dependence and kinematic viscosity on magnetoacoustic shocks are investigated. The numerical results are also presented for illustration. 相似文献
7.
The effect of large Larmor radius on the nonlinear behaviour of Alfvén waves propagating parallel to a uniform magnetic field in a compressible fluid is investigated with the aid of LLR-MHD equations. It is shown that asymptotic evolution of these waves is governed by the modified nonlinear Schrödinger equation. The dispersion is provided by the large Larmor radius effect in the magnetic field equation. It is suggested that these calculations can have a bearing on the investigation of the structure of MHD waves in both laboratory and space plasmas, e.g., imploding pinches, laser-blow-off plasma experiment, recent barium releases in the magnetosphere, plasma flow near small planetary bodies such as comets and plasma dynamic near collisionless shock fronts. 相似文献
8.
Nonlinear properties of the quantum magnetoacoustic wave are studied in electron-ion magnetoplasmas. In this regard, cylindrical Korteweg deVries (CKdV) equation is derived for small amplitude perturbations. The solution of the planar KdV equation is obtained using the tanh method and is subsequently used as an initial profile to solve the CKdV equation. It is found that the system under consideration admits compressive solitary structures. Finally, it is found that the amplitude as well as the width of the nonplanar magnetosonic solitary structure increases with the increase in the magnetic field whereas a decrease is observed with the increase in number density of the system. The present study may be beneficial to understand the nonlinear wave propagation in nonplanar geometries in dense plasmas. 相似文献
9.
In this concise review of the recent developments in relativistic shock theory in the Universe we restrict ourselves to shocks
that do not exhibit quantum effects. On the other hand, emphasis is given to the formation of shocks under both non-magnetised
and magnetised conditions. We only briefly discuss particle acceleration in relativistic shocks where much of the results
are still preliminary. Analytical theory is rather limited in predicting the real shock structure. Kinetic instability theory
is briefed including its predictions and limitations. A recent self-similar relativistic shock theory is described which predicts
the average long-term shock behaviour to be magnetised and to cause reasonable power-law distributions for energetic particles.
The main focus in this review is on numerical experiments on highly relativistic shocks in (i) pair and (ii) electron-nucleon
plasmas and their limitations. These simulations do not validate all predictions of analytic and self-similar theory and so
far they do not solve the injection problem and the self-modification by self-generated cosmic rays. The main results of the
numerical experiments discussed in this review are: (i) a confirmation of shock evolution in non-magnetised relativistic plasma
in 3D due to either the lepton-Weibel instability (in pair plasmas) or to the ion-Weibel instability; (ii) the sensitive dependence
of shock formation on upstream magnetisation which causes suppression of Weibel modes for large upstream magnetisation ratios
σ>10−3; (iii) the sensitive dependence of particle dynamics on the upstream magnetic inclination angle θ
Bn
, where particles of θ
Bn
>34° cannot escape upstream, leading to the distinction between ‘subluminal’ and ‘superluminal’ shocks; (iv) particles in
ultra-relativistic shocks can hardly overturn the shock and escape to upstream; they may oscillate around the shock ramp for
a long time, so to speak ‘surfing it’ and thereby becoming accelerated by a kind of SDA; (v) these particles form a power-law
tail on the downstream distribution; their limitations are pointed out; (vi) recently developed methods permit the calculation
of the radiation spectra emitted by the downstream high-energy particles; (vii) the Weibel-generated downstream magnetic fields
form large-amplitude vortices which could be advected by the downstream flow to large distances from the shock and possibly
contribute to an extended strong field region; (viii) if cosmic rays are included, Bell-like modes can generate upstream magnetic
turbulence at short and, by diffusive re-coupling, also long wavelengths in nearly parallel magnetic field shocks; (ix) advection
of such large-amplitude waves should cause periodic reformation of the quasi-parallel shock and eject large-amplitude magnetic
field vortices downstream where they contribute to turbulence and to maintaining an extended region of large magnetic fields. 相似文献
10.
L.R.S. Bianchi Type I string dust cosmological models with and without magnetic field following the techniques used by Letelier
and Stachel, is investigated. To get a determinate solution, we assume a conditionσ is proportional to scalar of expansion
θ where σ is shear and θ is scalar of expansion and which leads to A=ℓ B
nwhere n is a constant and ℓ is proportionality constant. Some special models are also investigated by introducing the transformation,
, which leads to Riccati type differential equation. The physical and geometrical aspects of the models are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The occurrence of magnetoacoustic surface waves at a single magnetic interface one side of which is field-free is explored for the case of non-parallel propagation. Phase-speeds and penetration depths of the waves are investigated for various Alfvén speeds, sound speeds and angles of propagation to the applied field. Both slow and fast magnetoacoustic surface waves can exist depending on the values of sound speeds and propagation angle. The fast waves penetrate more than the slow waves.The parallel propagation of fast and slow magnetoacoustic surface waves on a magnetic-magnetic interface is investigated. The slow surface wave is unable to propagate below a critical sound speed. In a low -plasma, only the fast mode exists (0 0). 相似文献
12.
M. Mehdipoor 《Astrophysics and Space Science》2012,338(1):73-79
Korteweg-de-Vries-Burger (K-dVB) equation is derived for ion acoustic shock waves in electron-positron-ion plasmas. Electrons
and positrons are considered superthermal and are effectively modeled by a kappa distribution in which ions are as cold fluid.
The analytical traveling wave solutions of the K-dVB equation investigated, through the (G′/G)-expansion method. These traveling wave solutions are expressed by hyperbolic function, trigonometric functions are rational
functions. When the parameters are taken special values, the shock waves are derived from the traveling waves. It is observed
that the amplitude ion acoustic shock waves increase as spectral index κ and kinematic viscosity η
i,0 increases in which with increasing positron density β and electron temperature σ the shock amplitude decreases. Also, numerically the effect different parameters on the nonlinearity A and dispersive B terms and wave velocity V investigated. 相似文献
13.
A consistent account of plasma turbulence in magnetohydrodynamics equations describing transport processes across the magnetic field is presented. The structure of the perpendicular shock wave generated in the solar atmosphere, as a result of either local disturbance of the magnetic field or dense plasma cloud motion with a frozen-in magnetic field, has been investigated. The region of parameters in the solar atmosphere at which the electron-ion relative drift velocity u exceeds the electron thermal velocity V
eand generation of radio emission becomes possible, has been determined. The plasma turbulence inside the front has been shown, under conditions of solar corona, not to cause the oscillation structure of shock front to break down. Under chromospheric conditions, the shock profile is aperiodical. Then, the condition u > Vecan be satisfied and shock waves having an Alfvén Mach number M which exceeds the critical value M
c 3.3 for aperiodical shock waves can exist (Eselevich et al., 1971a). Arguments are given in favour of the fact that perpendicular shock waves are generated in the Sun's atmosphere when dense plasma clouds, with a frozen-in magnetic field, are expanded. 相似文献
14.
Peter Goldreich 《Astrophysics and Space Science》2001,278(1-2):17-23
The inertial range of incompressible MHD turbulence is most conveniently described in terms of counter propagating waves.
Shear Alfvén waves control the cascade dynamics. Slow waves play a passive role and adopt the spectrum set by the shear Alfvén
waves. Cascades composed entirely of shear Alfvén waves do not generate a significant measure of slow waves. MHD turbulence
is anisotropic with energy cascading more rapidly along k
⊥ than along k
∥. Anisotropy increases with k
⊥ such that the excited modes are confined inside a cone bounded by k
∥∝ k
perp
2/3. The opening angle of the cone, θ(k
⊥)∝ k
⊥
-1/3, defines the scale dependent anisotropy. MHD turbulence is generically strong in the sense that the waves which comprise
it are critically damped. Nevertheless, deep inside the inertial range, turbulent fluctuations are small. Their energy density
is less than that of the background field by a factor θ2(k
⊥)≪. MHD cascades are best understood geometrically. Wave packets suffer distortions as they move along magnetic field lines
perturbed by counter propagating wave packets. Field lines perturbed by unidirectional waves map planes perpendicular to the
local field into each other. Shear Alfvén waves are responsible for the mapping's shear and slow waves for its dilatation.
The former exceeds the latter by θ-1(k
⊥)≫ 1 which accounts for dominance of the shear Alfvén waves in controlling the cascade dynamics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Properties of three-dimensional ion-acoustic solitary and shock waves accompining electron-positron-ion magnetoplasma with
high-energy (superthermal) electrons and positrons are investigated. For this purpose, a Zakharov-Kuznetsov-Burgers (ZKB)
equation is derived from the ion continuity equation, ion momentum equation with kinematic viscosity among ions fluid, electrons,
and positrons having kappa distribution together with the Poisson equation. The dependence of the solitary and shock excitations
characteristics on the parameter measuring the superthermality κ, the ion gyrofrequency Ω, the unperturbed positrons-to-ions density ratio ν, the viscosity parameter η, the direction cosine ℓ, the ion-to-electron temperature ratio σ
i
, and the electron-to-positron temperature ratio σ
p
have been investigated. Moreover, it is found that the parameters κ, Ω, ν, η, and ℓ lead to accelerate the particles, whereas the parameters σ
i
and σ
p
would lead to decelerate them. Numerical calculations reveal that the nonlinear pulses polarity are always positive. This
study could be useful to understand the nonlinear electrostatic excitations in interstellar medium. 相似文献
16.
A double discontinuity is a rarely observed compound structure composed of a slow shock layer and an adjoining rotational
discontinuity layer in the downstream region. In this paper, we report the observations of a double discontinuity detected
by Wind on May 15, 1997. This double discontinuity is found to be the front boundary of a magnetic cloud boundary layer. We
strictly identify the shock layer and the rotational discontinuity layer by using the high-resolution plasma and magnetic
field data from Wind. The observed jump conditions of the upstream and downstream region of the slow shock layer are in good
agreement with the Rankine – Hugoniot relations. The flow speeds in the shock frame U
n
<V
Acos θ
Bn
on both sides of the slow shock layer. In the upstream region, the slow Mach number M
s1=U
n1/V
s1 is 1.95 (above unity), and in the downstream region, the slow Mach number M
s2=U
n2/V
s2 is 0.31 (below unity). Here V
A and V
s represent the Alfvén speed and the local slow magnetosonic speed, respectively, and θ
Bn
is the angle between the direction of the magnetic field and the shock normal. The magnetic cloud boundary layer observed
by Wind was also detected by Geotail 48 min later when the spacecraft was located outside the bow shock of the magnetosphere.
However, Geotail observations showed that its front boundary was no longer a double discontinuity and the rotational discontinuity
layer disappeared, indicating that this double discontinuity was unstable when propagating from Wind to Geotail. 相似文献
17.
This article presents the first study of the head-on collision between two magnetoacoustic solitary waves (MASWs) in magnetized quantum plasma consisting of electrons, positrons, and ions, using the extended Poincaré-Lighthill-Kou (PLK) method. The effects of the magnetic field intensity, the positron to ion number density ratio, the quantum parameter, the Fermi temperature ratio, and plasma number density on the solitary wave collisions are investigated. It is shown that these factors significantly modify the phase shift. 相似文献
18.
We study a nonlinear mechanism for the excitation of kinetic Alfvén waves (KAWs) by fast magneto-acoustic waves (FWs) in the
solar atmosphere. Our focus is on the excitation of KAWs that have very small wavelengths in the direction perpendicular to
the background magnetic field. Because of their small perpendicular length scales, these waves are very efficient in the energy
exchange with plasmas and other waves. We show that the nonlinear coupling of the energy of the finite-amplitude FWs to the
small-scale KAWs can be much faster than other dissipation mechanisms for fast wave, such as electron viscous damping, Landau
damping, and modulational instability. The nonlinear damping of the FWs due to decay FW = KAW + KAW places a limit on the
amplitude of the magnetic field in the fast waves in the solar corona and solar-wind at the level B/B
0∼10−2. In turn, the nonlinearly excited small-scale KAWs undergo strong dissipation due to resistive or Landau damping and can
provide coronal and solar-wind heating. The transient coronal heating observed by Yohkoh and SOHO may be produced by the kinetic Alfvén waves that are excited by parametric decay of fast waves propagating from
the reconnection sites. 相似文献
19.
E. I. El-Awady H. Rizvi W. M. Moslem S. K. El-Labany A. Raouf M. Djebli 《Astrophysics and Space Science》2014,349(1):5-10
Magnetosonic rogue waves (rogons) are investigated in an electron-ion plasma by deriving the nonlinear Schrödinger (NLS) equation for low frequency limit. The first- and second-order rogue wave solutions of the NLS equation are obtained analytically and examined numerically. It is found that for dense plasma and stronger magnetic field the nonlinearity decreases, which causes the rogon amplitude becomes shorter. However, the electron temperature pumping more energy to the background waves which are sucked to create rogue waves with taller amplitudes. 相似文献
20.
A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods.
In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P
1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P
2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift
of some groups of fibers for the long-period wavelet tadpoles (P
3) and to the frequency drift of individual fibers for the short-period tadpoles (P
2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence
of several wave trains in the fibers’ source. While the long-period wave trains trigger or modulate a whole group of fibers,
the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. 相似文献