Alfven Solitons Research Articles

An analysis of unidimensional soliton gas models of magnetohydrodynamic turbulence in the solar wind

Two statistical models of Alfven solitons are compared whose evolution is described by the one-dimensional derivative nonlinear Schroedinger (DNLS) equation, contrasting their predictions with solar wind observations. Both distribution functions give the same mean number of solitons. One of the distribution functions follows an exponential law with soliton energy and the other follows a power law; the latter gives better results than the former. Within these models, the variation of the observed spectra with the heliocentric distance can be explained. This variation is related to the radial dependence of the mean level of modulation instability in the medium. 47 refs.

Nonlinear two‐fluid hydromagnetic waves in the solar wind: Rotational discontinuity, soliton, and finite‐extent Alfvén wave train solutions

Nonlinear one‐dimensional constant‐profile hydromagnetic wave solutions are obtained in finite‐temperature two‐fluid collisionless plasmas under adiabatic equation of state. The nonlinear wave solutions can be classified according to the wavelength. The long‐wavelength solutions are circularly polarized incompressible oblique Alfvén wave trains with wavelength greater than hundreds of ion inertial length. The oblique wave train solutions can explain the high degree of alignment between the local average magnetic field and the wave normal direction observed in the solar wind. The short‐wavelength solutions include rarefaction fast solitons, compression slow solitons, Alfvén solitons and rotational discontinuities, with wavelength of several tens of ion inertial length, provided that the upstream flow speed is less than the fast‐mode speed. The Alfvén solitons and rotational discontinuities are super‐Alfvénic compression waves if the upstream Alfvén‐mode speed is greater than the sound speed; otherwise, they are sub‐Alfvénic rarefaction waves. The density and magnetic field variations of these short‐wavelength waves are shown to obey the following two rules: (1) all compression waves are left‐hand polarized and all rarefaction waves are right‐hand polarized, due to the ion inertial effect, (2) the density variation and the magnetic field magnitude variation are in phase if the flow is supersonic, but out of phase if the flow is subsonic, which is a consequence of conservation of the momentum flux. The two‐fluid rotational discontinuity solution obtained in this study is highly circularly polarized, with a variable angular rotation rate. The total angle of rotation is limited to less than or equal to 180°, which is consistent with the rotational discontinuity observed in the solar wind. The upstream flow speed of the two‐fluid rotational discontinuity must deviate slightly from the Alfvén‐mode speed; the downstream flow speed is equal to the local sound speed. The formation of the two‐fluid rotational discontinuity depends critically on the dispersion effect which converts the Alfvén mode to the ion acoustic mode.

Coherent radiation mechanism for cometary kilometric radiation

A mechanism involving nonlinear interaction of Alfven solitons and Langmuir waves is proposed to explain the cometary kilometric radiation (CKR) observed in the vicinity of comet Halley. According to this model, the frequency of the radiation emitted depends on the position of the interaction (or emission) region relative to the comet; higher frequencies being emitted when this region is closer to the comet. The CKR source is shown to lie at a distance ranging between 10 to the 5th and 2 x 10 to the 6th km from the comet nucleus. Several observed features of CKR, type D, S, and C emissions, can be explained nicely by this model. 24 references.

Nonlinear phenomena in plasmas. Problems on nonlinear phenomena in plasma. Part I.

In the part II, we discuss the reduction perturbation method, birth of solitons, the inverse scattering transformation for the Korteweg-de Vries equation, generalization of the inverse scattering transformation methods, propagation of the Alfven solitons and soliton-like behaviour of vortex motion. Problems on chaos and stochasticity in nonlinear dynamics will be discussed in the part III.

Low-frequency plasma turbulence during solar wind-comet interaction

The pick up cometary ion distributions are shown to excite Alfvenic mode instabilities, slow ion-acoustic mode instability and a lower hybrid instability during solar wind-comet interaction. The growth rates of all these instabilities become larger as the comet is approached. The lower hybrid instability is shown to account for the low-frequency 0–300 Hz electrostatic turbulence observed near comet Halley. The Alfven modes can grow to large amplitudes and become modulationally unstable, in the presence of low-frequency density fluctuations, going over to envelope Alfven solitons. A model consisting of a gas of Alfven solitons is suggested to explain the hydromagnetic turbulence observed near comet Halley and comet Giacobini-Zinner.

Nonlinear propagation of Alfv�n waves in cometary plasmas

Large-amplitude Alfven waves propagating along the guide magnetic field in a three-component plasma are shown to be spatially localized due to their nonlinear interaction with nonresonant electrostatic density fluctuations. A new class of subsonic Alfven soliton solutions are found to exist in the three-component plasma. The Alfven solitons can be relevant in explaining the properties of hydromagnetic turbulence near the comets.

Particle interactions with Alfv�n solitons

We compute velocity and the corresponding energy changes due to non-resonant interactions of protons with Alfven solitons. It is seen that the protons heat in the perpendicular direction but associated with this is a cooling in the parallel direction.

Solitons in plasma with a hall dispersion

A system of equations of perfect magnetohydrodynamics is considered with allowance for Hall currents. The study of one-dimensional steady solutions which are damped at infinity can be reduced to the investigation of a Hamiltonian dynamic system with right-hand sides that are not single valued. A qualitative investigation of the system is carried out, with the determination of the region of existence of the given solutions. The solutions have the form of solitary waves — solitons. An exact solution in quadratures is obtained, which describes the structure of the solitons. The existence of two solitons of the Alfven type is indicated. The existence domain of the corresponding solutions is analyzed. In the limiting cases of magnetosonic and Alfven solitons, the solutions are expressed in explicit form in elementary functions.

Alfven solitons in a relativistic electron-position plasma. I. Hydrodynamic theory

Nonlinear Alfven waves, propagating along an equilibrium magnetic field, are studied on the base of relativistic isotropic hydrodynamics. Alfven solitons of moving-wave and wave-packet type are considered. The results of Sakai and Kawata (1980) concerning the Alfven solitons of moving-wave type are revised. New expressions for the parameters characterizing these solitons are obtained.

Alfven solitons in a relativistic electron-positron plasma. II. Kinetic theory

For pt.I see ibid., vol.27, no.5, p.527-37 (1985). Kinetic theory of nonlinear Alfven waves propagating along the equilibrium magnetic field in a relativistic electron-positron plasma is presented. Comparison of the results of kinetic and hydrodynamic approaches is performed. Excitation of the Alfven solitons by a beam of high-energy particles is discussed. Results obtained are used for the interpretation of the microstructure of radio radiation of pulsars.

A soliton gas model for astrophysical magnetized plasma turbulence

Plasma turbulence is considered as an ensemble of solitons. The derivation of the Alfven soliton by Spangler and Sheering (1981) is reviewed, and expressions are derived for the magnetic irregularity spectrum and the relationship between the magnetic and density irregularity power spectra. A derived expression also provides the answer to the question of the correlation between magnetic field and density enhancements. The properties of the turbulence model are compared with observations of plasma turbulence in the solar wind, and are found to reasonably account for them.