不均匀等离子体中电磁波与Langmuir波的相互作用

通过理论研究与数值计算,不均匀等离子体中Langmuir波与电磁波的相互作用及其线性模式转换规律得到了充分的展示.导出了不均匀等离子体中的电磁色散关系,研究了入射电磁波或Langmuir波在通过不均匀等离子体的过程中发生转换的物理过程,以及波的传播矢量随空间坐标变化的关系,并对电磁波与Langmuir波相互作用的机理进行了讨论.研究结果对密度梯度所驱动的等离子体波产生电磁辐射的研究具有重要意义. 关键词： 电磁波 Langmuir波 不均匀等离子体 线性模式转换     

Magnetic instability in an inhomogeneous plasma in an intense electromagnetic wave

Radiophysics Research Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 2, pp. 170–176, February, 1990.     

Resonant interaction of an electromagnetic wave with an inhomogeneous plasma slab

Resonant interaction at oblique incidence of an electromagnetic wave on an inhomogeneous plasma slab is studied. The time evolution of this interaction is solved numerically from two-fluid equations, adiabatic equation for electron pressure and from Maxwell equations. It is shown that the electromagnetic energy of an incident wave is transformed both into the heat energy and into the energy of plasma oscillations in the direction of density gradient. The distribution of the transformed energy between the heat energy and the energy of plasma oscillations is strongly dependent on the plasma temperature. The ratio of heat energy to the energy of plasma oscillations is growing with growing temperature. The plasma oscillations are generated by magnetic induction of the penetrating wave. In a cold plasma they are generated especially in the overdense region and their frequency is equal to local plasma frequency. The electric field in the direction of plasma gradient has a form of a wave packet whose envelope reaches a maximum at resonance. The characteristic wavelength in the wave packet decreases and the amplitude of the packet increases with the time.     

Propagation of a transient electromagnetic disturbance in an inhomogeneous, collisional, Magnetized plasma

Summary The time response of an anisotropic, inhomogeneous magnetized plasma to a time-dependent externally applied electric field is studied. The plasma is considered as a conducting medium embedded in a static magnetic fieldB _o, with finite and constant parallel conductivity σ_∥ and normal conductivity σ_⊥ exponentially varying; a constant ion polarization conductivity (σ_pol) normal toB ₀ is also included. The driving termE ₀ is assumed to be normal to the ambient magnetic field, with a space dependence only in the (E ₀, B₀)-plane (two-dimensional case). The problem is treated as an initial (in time) and boundary (in space) value problem, and an analytic solution is obtained for the time response of the system to a unit step of electric field; the solution for any other driving field is then given via a convolution integral. This model can be used in particular to study the propagation through the ionosphere of ULF waves generated by the motion of an artificially created ion cloud in the upperF region. Moreover, the mathematical technique is rather general, so it may be used also for different plasma models.

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Riassunto Si presenta lo studio della risposta temporale (transitorio) di un plasma magnetizzato, anisotropo e inomogeneo ad un campo elettrico esterno impresso. Il plasma è trattato come un mezzo conduttore, immerso in un campo magnetico staticoB ₀, la cui conducibilità elettrica parallela al campo magnetico σ_∥ è costante, mentre la conducibilità normale σ_⊥ varia esponenzialmente nello spazio; si considera inoltre una conducibilità dovuta alla polarizzazione degli ioni (σ_pol) costante e normale aB ₀. Il campo impressoE ₀ è assunto normale al campo magnetico ambiente con dipendenza spaziale solo nel piano (E ₀, B₀) (caso bidimensionale). In queste ipotesi si perviene ad un problema ai valori iniziali e al contorno, e si deriva una soluzione analitica per la risposta transitoria del sistema ad un gradino di campo elettrico impresso; la soluzione per una qualsiasi funzione di campo applicato è data come integrale di convoluzione con la risposta al gradino. Questo modello può essere usato, in particolare, per studiare la propagazione attraverso la ionosfera di un'onda ULF generata dal moto di una nuvola ionica creata artificialmente nella parte superiore della regioneF. Un ulteriore interesse deriva dal fatto che, essendo la tecnica matematica utilizzata molto generale, questa può essere applicata pure a differenti modelli di plasma.

     

Propagation of electromagnetic waves in hot magnetoactive plasma

The paper derives the general form of the tensor of dielectric permittivity? _ij(ω,k), Eq. (15), of non-relativistic hot magnetoactive collisionless plasma taking into consideration the influence of spatial dispersion. The general form of the tensor? _ij(ω,k) is used to express the tensorε _ij(ω,k) in the region of weak and strong spatial dispersion and in some special cases. A general dispersion equation (30) is derived and an analysis is made of the waves propagating in hot magnetoactive plasma. The expressions derived are used to investigate the damping of a right-handed circularly polarized wave propagating in hot magnetoactive plasma in the direction of the magnetic field.     

Nonlinear modulation of a powerful electromagnetic wave in a weakly inhomogeneous plasma

We show the possibility for nonlinear trapping of a Langmuir wave in the region of weak inhomogeneity of plasma under parametric interaction with a powerful electromagnetic wave. Under overcritical conditions in the presence of dissipation and imperfect reflection, space-time amplitude correlations emerge and wave soliton structures are then formed. Powerful regular oscillations appear in the system, leading to a giant modulation of the pump pulse. The Langmuir nonlinearity contribution increases with the above-threshold value, which results in a sharp increase and compression of solitary waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 9, pp. 1096–1102, September, 1996.     

Propagation of the electromagnetic ion-cyclotron wave in a fusion plasma

The propagation of the electromagnetic ion-cyclotron wave in a fusion plasma described by a loss-cone structure is discussed. The wavelength is assumed to be much larger than the ion Larmour radius and the ion plasma frequency ≫ the ion-cyclotron frequency. The two modes that propagate in the plasma interact strongly and fuse together under certain conditions making the plasma unstable. The coalescence of the modes is found to decrease with an increase in electron temperature.     

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提出碰撞吸收型等离子体的等效折射指数,重新计算了折射角,并与利用常规方法得到的折射角进行了比较。分析了等离子体密度和碰撞频率对折射角的影响。考察了斜入射电磁波在吸收型等离子体中的折射特性,并以一维非均匀碰撞吸收型等离子体为例,对斜入射电磁波的反射特性进行了考察。结果表明,等效折射指数的概念涵盖了入射角度的影响,在考察斜入射时更准确、便捷。     

Relativistic effects on electromagnetic wave propagation in a cold inhomogeneous electron plasma

We construct a method which permits to investigate the propagation of a travelling wave in different cases. We present the results we obtained in the case of an inhomogeneous plasma taking into account relativistic effects.