Effect of external magnetic field on nonlinear propagation of cylindrical magnetoacoustic soliton waves in quantum plasma

The propagation of magnetoacoustic solitary waves is investigated in magnetized quantum plasma consisting of cold ions and hot electrons. By using the quantum magnetohydrodynamic (QMHD) model, the nonlinear characteristics of different features of solitary waves in an electron-ion quantum magnetoplasma are investigated. Magnetoacoustic solitary waves are stationary solutions of the equations composed of the nonlinear mass and momentum continuity, together with the Maxwell's equations. The important quantum-mechanical effects including the quantum statistical and diffraction are examined numerically on the profiles of the solitons. It is found that the non-dimensional characteristic of the quantum parameter plays a significant role in the formation of the solitons.     

XY spin fluid in an external magnetic field

A method of integral equations is developed to study anisotropic fluids with planar spins in an external field. As a result, the calculations for these systems appear to be no more difficult than those for ordinary homogeneous liquids. The approach proposed is applied to the ferromagnetic XY spin fluid in a magnetic field using a soft mean spherical closure and the Born-Green-Yvon equation. This provides an accurate reproduction of the complicated phase diagram behavior obtained by cumbersome Gibbs ensemble simulation and multiple histogram reweighting techniques.     

Effective field theory approach to light propagation in an external magnetic field

The recent PVLAS experiment observed rotation of polarization and ellipticity when a linearly polarized laser beam passes through a transverse magnetic field. The phenomenon cannot be explained in conventional QED. We attempt to accommodate the result by employing an effective theory for the electromagnetic field alone. No new particles with a mass of order the laser frequency or below are assumed. To quartic terms in the field strength, a parity-violating term appears besides the two ordinary terms. The rotation of polarization and ellipticity are computed for parity-asymmetric and -symmetric experimental set-ups. While rotation occurs in an ideal asymmetric case and has the same magnitude as ellipticity, it disappears in a symmetric set-up like PVLAS. This would mean that we have to appeal to some low-mass new particles with nontrivial interactions with photons to understand the PVLAS result. PACS 12.20.-m; 12.20.Fv; 42.25.Lc; 42.25.Ja     

Wave propagation in strongly coupled classical plasmas in an external magnetic field

When a small perturbation is applied to the plasma dispersion, a small shift of frequency due to correlation occurs. This is justified even for strong coupling, since the effect is proportional tok ² (k is the wave vector) and it is sufficient to consider thek 0 limit. Then by solving the dispersion relations for, the shift of frequency due to correlation, at different angles of propagation, we obtain all information needed. The plasma modes in which we are primarily interested are the whistler and the extraordinary modes. In this work the STLS (Singwi, Tosi, Land, and Sjolander) approximation scheme is used. It is seen that the correlational effects enter only through terms of orderk ⁶ for the whistler mode and terms of orderk ² for the nonresonant situation of the extraordinary mode.     

Relativistic excitation of beat waves in a plasma in the presence of an external magnetic field

Summary A theoretical investigation of the nonlinear relativistic excitation of the longitudinal electron plasma wave at the beat frequency of two colinear laser beams has been made in a hot, collisionless and homogeneous plasma in the presence of an external magnetic field. The relativistic Vlasov equation has been solved to obtain the nonlinear response of magnetized electrons. It is observed that the power conversion efficiency of the excited-electron plasma wave at the difference frequency is much higher for the relativistic calculation than that for the nonrelativistic calculations. It is further noticed that the power conversion efficiency of the beat wave excitation increases slowly with the external magnetic field when the colinear laser beams propagate transverse to the direction of the external magnetic field, whereas it is almost unaffected when the incident waves propagate parallel to the direction of the magnetic field.

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Riassunto Si è effettuata una ricerca teorica dell'eccitazione relativistica nonlineare dell'onda longitudinale del plasma dell'elettrone ad una frequenza di battimento di due raggi laser colineari in un plasma omogeneo, caldo e senza collisioni, in presenza di un campo magnetico esterno. è stata risolta l'equazione di Vlasov relativistica per ottenere la risposta nonlineare di elettroni magnetizzati. Si osserva che l'efficacia di conversione di potenza dell'onda di plasma degli elettroni eccitati alla frequenza di differenza è molto superiore per il calcolo relativistico che quella per i calcoli non relativistici. Si nota inoltre che l'efficacia di conversione di potenza dell'eccitazione d'onda di battimento aumenta lentamente con il campo magnetico esterno quando i raggi laser colineari si propagano trasversalmente rispetto alla direzione del campo magnetico esterno, mentre rimane quasi immutata quando le onde incidenti si propagano parallelamente alla direzione del campo magnetico.

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Резюме Проводится теоретическое исследование нелинейного релятивистского возбуждения продольных электронных плазменных волн на частоте биений двух соосных лазерных пучков в торячей, бесстолкновительной и однородной плазме в присутствии внешнего магнитного поля. Чтобы получить нелинейный отклик электронов в магнитном поле, решается релятивистское уравнение Власова. Получается, что эффективность конверсии мощности для возбужденной электронной плазменной волны на разностной частоте оказывается много большей для релятивистских вычислений, чем для нерелятивистских вычислений. Затем отмечается, что эффективность возбуждения биений увеличивается медленно с ростом внешнего магнитного поля, когда соосные лазерные пучки распространяются поперек направления внешнего магнитного поля, тогда как эффективность возбуждения почти не изменяется, когда падающие волны распространяются параллельно направлению магнитного поля.

     

On a theory of surface waves in a smoothly inhomogeneous plasma in an external magnetic field

A theory of surface waves in a magnetoactive plasma with smooth boundaries has been developed. A dispersion equation for surface waves has been derived for a linear law of density change at the plasma boundary. The frequencies of surface waves and their collisionless damping rates have been determined. A generalization to an arbitrary density profile at the plasma boundary is given. The collisions have been taken into account, and the application of the Landau rule in the theory of surface wave damping in a spatially inhomogeneous magnetoactive collisional plasma has been clarified.     

Density waves in quark matter within the Nambu-Jona-Lasinio model in an external magnetic field

The possibility of forming static dual scalar and pseudo-scalar density wave condensates in dense quark matter is considered for the Nambu-Jona-Lasinio model in an external magnetic field. Within a mean-field approximation, the effective potential of the theory is obtained and its extrema are numerically studied and a phase diagram of the system is constructed. It is shown that the presence of a magnetic field favors the formation of spatially inhomogeneous condensate configurations at low temperatures.     

Effect of annealing in an external magnetic field on the magnetic texture of Mo-containing nanocrystalline alloys

The magnetic texture of (Fe_1?x Co_x)₇₆Mo₈Cu₁B₁₅ (x = 0, 0.5) nanocrystalline alloys is studied for different amounts of nanocrystalline grains. The originally amorphous alloys were annealed in external longitudinal and transverse magnetic fields of 0.025 T and 0.8T, respectively. Mössbauer measurements were carried out at room and liquid nitrogen temperatures in order to gain information on the hyperfine interactions and the orientation of the magnetization. The obtained results are compared with those received from zero-field annealed samples. Magneto-optical Kerr effect (MOKE) was applied for the investigation of possible changes at the surface of the x = 0 ribbon as a function of annealing temperature and applied magnetic field. A combination of uniaxial anisotropy, which originates from the shape anisotropy, and four-fold anisotropy, which is a contribution from crystallites of nanometre size embedded in the residual amorphous matrix, is unveiled.     

Effect of an external magnetic field on Landau damping in carbon nanotubes

A quantum-mechanical formula for describing the dependence of the longitudinal permittivity of a nanotube on its characteristic parameters and the magnetic field strength was derived. The imaginary part of the permittivity was isolated, and the cases of a Boltzmann and degenerate electron gas were examined. For a degenerate electron gas, asymptotic expressions for absorption in the short- and long-wave ranges were obtained. It was demonstrated that the absorption coefficient for a longitudinal electromagnetic wave exhibits Aharonov-Bohm oscillations.     

Influence of external magnetic field on dust acoustic waves in a capacitive RF discharge

This paper reports experiments on self-excited dust acoustic waves (DAWs) and its propagation characteristics in a magnetized rf discharge plasma. The DAWs are spontaneously excited in dusty plasma after adding more particles in the confining potential well and found to propagate in the direction of streaming ions. The spontaneous excitation of such low-frequency modes is possible due to the instabilities associated with streaming ions through the dust grain medium. The background E-field and neutral pressure determine the stability of excited DAWs. The characteristics of DAWs strongly depend on the strength of external magnetic field. The magnetic field of strength B < 0.05 T only modifies the characteristics of propagating waves in dusty plasma at moderate power and pressure, P = 3.5 W and p = 27 Pa, respectively. It is found that DAWs start to be damped with increasing the magnetic field beyond B > 0.05 T and get completely damped at higher magnetic field B ∼ 0.13 T. After lowering the power and pressure to 3 W and 23 Pa respectively, the excited DAWs in the absence of B are slightly unstable. In this case, the magnetic field only stabilizes and modifies the propagation characteristics of DAWs while the strength of B is increased up to 0.1 T or even higher. The modification of the sheath electric field where particles are confined in the presence of the external magnetic field is the main cause of the modification and damping of the DAWs in a magnetized rf discharge plasma.     

Effect of a periodic magnetic field on waves in a cold plasma

The effect of a spatially-uniform periodic magnetic field on waves propagating perpendicular to it in a cold plasma is considered. Assuming that the pump field is weak, the method of multiple time scales is used to treat the problem. The results show that, unlike the pump electric field, the pump magnetic field does not produce any parametric excitation of the transverse waves, no matter what the value of the frequency mismatch is.     

Electromagnetic waves in a round rod in the presence of an arbitrarily directed external magnetic field or anisotropy axis

A rigorous theory of the propagation of electromagnetic waves in round anisotropic and semiconductor rods in the presence of an arbitrarily directed anisotropy axis or external magnetic field is developed. New types of independent waves are discovered. Exact dispersion equations are obtained for them, which define the dependence of their spectral characteristics on the parameters of the semiconductor or anisotropic crystal and on the magnitude and direction of the constant external magnetic field. The results of numerical investigations for rods made from a semiconductor or a uniaxial crystal are presented. Zh. Tekh. Fiz. 67, 86–91 (July 1997)     

Light propagation in a strong external magnetic field with regard to quantum corrections

Linearized motion equations for electromagnetic wave field in the external magnetic field have been solved for the PVLAS experiment configuration within the low-energy approximation of quantum electrodynamics. It has been shown that the wave propagation velocity depends on the initial direction of the plane of wave polarization. Dispersion laws corresponding to the waves with mutually perpendicular directions of polarization have been established. The dependence of ellipticity of laser radiation field on initial polarization and the value of the external magnetic field has been obtained. The ellipticity parameter for the configuration of the system used in the PVLAS experiment has been found.