On the envelope soliton near critical density in a plasma with cold ions and two-temperature electrons

Summary We have analysed the formation of envelope soliton near critical density in a plasma consisting of two-temperature electrons and cold ions. The non-linear Schr?dinger-like equation obtained isiφ _t +pφ _xx +q|φ|⁴φ=0 which we call the modified non-linear Schr?dinger equation. It is also observed that this approach leads to a physical situation where a linear combination of both the modified and usual NLS equations holds, in the formiφ _t +pφ _xx +q ₁|φ|²φ +q ₂|φ|⁴φ=0. It is demonstrated through graphical analysis thatq ₁,q ₂, thought of as a function of β(=T _el/T _eh), behave in opposite way. That is, whenq ₁ grows,q ₂ decays, or vice versa. Lastly we demonstrate that this equation can sustain a type of solution other than the usual solitary profile. The form of such a wave is also depicted graphically.     

Decay and modulation instabilities of beat waves in a plasma

Summary A large-amplitude beat wave excited at the beat frequency of two copropagating laser beams is extremely unstable and suffers strong three- and fourwave parametric instabilities with large growth rates. The relativistic effects are seen to be negligible on both the decay and modulation instabilities. However, the growth rates of these instabilities are sensitive functions of the plasma parameters. The authors of this paper have agreed to not receive the proofs for correction.     

Ultrarelativistic excitation of beat waves in a hot magnetized plasma

Summary A theoretical investigation is made on the nonlinear relativistic excitation of an electrostatic electron plasma wave at the beat frequency of two high-power colinear laser beams in a hot, homogeneous and magnetized plasma. The relativistic Vlasov equation expressed in gyrokinetic variables has been employed to find the nonlinear response of the magnetized plasma electrons. It is noted that the power density associated with the excited beat wave is much higher for the relativistic consideration than that for the nonrelativistic consideration. The authors of this paper have agreed to not receive the proofs for correction.     

Hydromagnetic surface waves in a moving compressible plasma column

Summary The dispersive characteristic of hydromagnetic surface waves along a plasma-plasma interface when one of the fluids has a relative motion has been studied as a function of the compressibility factors ₁/V ₁, wheres ₁ andV ₁ are the acoustic and Alfvén wave speed in one of the media. Both slow and fast magnetosonic surface waves for each symmetric and asymmetric modes can exist. The nature and existence of these modes depend on the values ofs ₁/V ₁ and ϑ, the angle of wave propagation. The phase velocity of the slow wave increases whereas for the fast wave it decreases with increase in the angle ϑ. The authors of this paper have agreed to not receive the proofs for correction.     

Instability of plasma waves in an electromagnetic field

Summary In the presence of a weak laser field the plasma scattering by electrons is discussed.

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Riassunto In presenza di un campo laser debole, si discute la diffusione del plasma mediante elettroni.

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Резюме В присутствии слабого лазерного поля обсуждается рассеяние плазмы на электронах.

     

Head-on collision of ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma

The head-on collision between two ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma has been investigated. By using the extended Poincaré-Lighthill-Kuo perturbation method, we obtain the KdV equation and the analytical phase shift after the head-on collision of two solitary waves in this three-component plasma. The effects of the ratio of electron temperature to positron temperature, and the ratio of the number density of positrons to that of electrons on the phase shift are studied. It is found that these parameters can significantly influence the phase shifts of the solitons. Moreover, the compressive solitary wave can propagate in this system.     

On a kinetic approach to the modulational stability of envelope solitons in a relativistic plasma in an external electric field

Summary The formation of envelope solitons is discussed in a relativistic plasma under the influence of a fluctuating electric field. We use the kinetic-theory approach for our analysis. Due to the larger inertia, only the electrons are considered to be relativistic and the ions to be nonrelativistic. A NLS equation is derived describing the motion of the solitary wave. This NLS equation actually comes from an approximation of a pair of equations which can be considered to be a relativistic generalisation of the Zakharov equation. We next discuss the exact form of the envelope solitary-wave solution of the NLS equation and the modulation stability of such a wave. When the density, momentum and energy of such wave packets are fixeda priori, conditions are derived for the parameters of the problem from such stability consideration.     

Effect of self-generated magnetic field on the two-plasmon decay instability in a laser-produced plasma

Summary In this paper we have made a theoretical investigation on the two-plasmon decay instability of laser radiation in the presence of the selfgenerated magnetic field at the quarter-critical density region in a laserproduced plasma. The Vlasov equation in terms of guiding centre coordinates has been employed to obtain the nonlinear response of electrons in the plasma. The threshold power density of the incident laser radiation for the two-plasmon decay instability is always exceeded in currently employed power densities in laser-target experiments and above the threshold the growth rate of the instability is quite large. It is also noticed that the selfgenerated magnetic field enhances the threshold to a large extent, thus drastically reducing the growth rate of the instability. To speed up publication, the author of this paper has agreed to not receive the proofs for correction     

MHD cylindrical shock wave in self-gravitating gas

Summary Similarity solutions of the propagation of cylindrical blast waves through a self-gravitating polytropic gas caused by an instantaneous release of finite energy are investigated theoretically including the influence of transverse magnetic field. A comparative study of the distributions of velocity, density, mass, pressure, temperature and magnetic field has been illustrated through figures. The authors of this paper have agreed to not receive the proofs for correction.     

The fully relativistic dielectric tensor for electron cyclotron interaction in a Maxwellian plasma

Summary A thorough analytical and numerical study of the fully relativistic dielectric tensor relevant to the electron cyclotron propagation and absorption in a Maxwellian plasma is presented for arbitrary values of the wave refractive index parallel to the equilibrium magnetic field. Both the Hermitian and the anti-Hermitian part are calculated relativistically and, in particular, as for the anti-Hermitian part, the finite Larmor radius effects are accounted for to any order. Limiting forms are obtained along with a detailed numerical comparison with the nonrelativistic form.

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Riassunto Si calcola, sia analiticamente che numericamente, il tensore dielettrico completamente relativistico di rilevanza nella propagazione e nell'assorbilnento ciclotronico elettronico in un plasma maxwelliano, per valori arbitrari dell'indice di rifrazione parallelo al campo magnetico di equilibrio. Si tien conto degli effetti relativistici sia nella parte Hermitiana che nella parte anti-Hermitiana, in questa ultima pure gli effetti di raggio di Larmor finito sono inclusi a tutti gli ordini. Si ottengono e si discutono limiti significativi e si presenta un dettagliato confronto numerico con la forma non relativistica del tensore dielettrico.

     

Ion acoustic soliton propagation in a magnetized relativistic plasma

Summary The Korteweg-de Vries equation for ion acoustic waves in the presence of weakly relativistic ion streaming velocity is derived in a magnetic plasma. It is found that relativistic effects are important in the solitary wave propagation for both fast and slow modes. Earlier results are reconfirmed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Relativistic and nonrelativistic modulational instability of a laser radiation in an unmagnetized laser-produced plasma: Kinetic theory

Summary This paper presents a rigorous theoretical investigation of the relativistic and nonrelativistic modulational instability of a high-power laser radiation propagating in a collisionless and unmagnetized laser-produced plasma. The kinetic equationviz. the relativistic Vlasov equation has been employed to find the nonlinear response of electrons for this four-wave parametric process in the plasma. The actual motivation behind this theoretical investigation is to find the relativistic effect on this four-wave paremetric processviz. the modulational instability. Here, it can be noted that the modulational instability of the laser radiation under our situation has not a large but considerable relativistic effect and for the same set of plasma parameters the growth rate of the instability in ultrarelativistic consideration is approximately three times higher than that in the nonrelativistic consideration. The authors of this paper have agreed to not rective the proofs for correction.     

Similarity solutions of isothermal flows behind a MGD blast wave in an inhomogeneous medium

Summary Self-similar solutions of isothermal flows behind a cylindrical magnetogasdynamic blast wave have been obtained. A strong cylindrical shock wave generated by a sudden line source explosion in an inhomogeneous medium of electrically conducting gas has been studied. Numerical and analytical treatments have been presented and a uniformly valid distribution of pressure, density and velocity profiles has been determined and the magnetic-field effects on the flow distributions have been investigated. The shock propagation law is determined by extending Whitham’s rule for a MGD flow with infinite electrical conductivity.

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Riassunto Si sono ottenute soluzioni autosimili di flussi isotermici dietro un’onda espansiva, magnetogasdinamica, cilindrica. è stata studiata un’onda d’urto forte cilindrica generata da un’improvvisa esplosione a sorgente lineare in un mezzo non omogeneo di un gas elettricamente conduttore. Si presentano trattamenti numerici e analitici e si è determinata una distribuzione uniformemente valida dei profili di pressione, densità e velocità e si sono studiati gli effetti del campo magnetico sulle distribuzioni del flusso. La legge di propagazione dell’urto si determina estendendo la regola di Whitham per un flusso MGD con conduttività elettrica infinita.

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Резюме Получются самоподобные решения для изотермических потоков за цилиндрической магнитогазодимамической ударной. Исследется сильная цилиндческая ударная волна, которая обрзуетсяв резуль↦ате внеапного взрыва линейного истоника в неоднородной среде электрически проводящего газа. Проводятся численное и аналитическое рассмотрение. Определяжтся распредение давления, профили плотности и скорости. йсследуется влияние магнитного поля на распредение потока. Определется закон распространения ударной волны, обобшая правило Витама для магнитогазодинамического потока с бесконечной электрической проводимостью.

     

Theory of weak modified electron acoustic double layers

Summary We have obtained the double-layer solutions for the small-amplitude modified electron acoustic waves propagating in a plasma having one ion and two electron components. No DLs solutions are found to exist when the temperature of the free and trapped particles is considered to be the same for all the species. However, when the effects of the reflected hot electrons are considered, DL solutions are found to exist.

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Riassunto Si sono ottenute soluzioni del doppio strato per onde acustiche modificate dall’elettrone di piccola ampiezza, che si propagano in un plasma avente una componente ionica e 2 componenti elettroniche. Si trova che non esistono soluzioni DL quando la temperatura delle particelle libere e intrappolate si considera stessa per tutte le specie. Tuttavia si trova che le soluzioni DL esistono quando si considerano gli effetti degli elettroni caldi riflessi.

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Резюме Мы получили решения для двойных слоев в случае акустических волн с малой амплитудой, распространяющихся в плазме, имеющей одну ионную и две электронные компоненты. Показано, что не существуют решения для двойных слоев, когда температура свободных и захваченных частиц является одинаковой для всех компонент. Однако, когда учитывается влияние отраженных горячих электронов, решения для двойных слоев существуют.

     

Comments on heuristic models for electron turbulence

Summary The difficulties imposed by the largely nonlinear character of the differential equations governing turbulence resulted in many proposals for empirical models. We shall prove that some often used models are incorrect as they are clearly not properly normalized.

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Riassunto Le difficoltà imposte dal carattere largamente non lineare delle equazioni differenziali che regolano la turbolenza hanno dato come risultato molte proposte per modelli empirici. Si prova che alcuni modelli spesso usati non sono corretti poiché non possono essere normalizzati appositamente.

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Резюме Трудности, накладываемые нелинейным характером дифференциальных уравнений, описывающих турбулентность, приводят к большому числу эмпирических моделей. Мы доказываем, что некоторые часто используемые модели не являются корректными, так как они не нормированы надлежащим образом.

     

Drift dissipative instabilities in hybrid frequency range

Summary The instabilities of electron convection mode in a collisional plasma including electromagnetic effects are investigated. It is found that all the three solutions of the linear-dispersion relation are unstable. It is shown that the ion temperature fluctuations can play a stabilizing role. An application to a typical low-temperature plasma is discussed. The authors of this paper have agreed to not receive the proofs for correction.     

Cylindrical blast wave with radiation heat flux in self-gravitating gas

Summary A similarity solution of cylindrical shock waves propagating in a uniform atmosphere through self-gravitating gas including the influence of radiation heat flux has been investigated. This problem has also been studied in isothermal conditions. The total energy of the line explosion is assumed to be constant. The solutions of the problem are compared with the results obtained in adiabatic conditions through figures.     

Modulational instability of ion—acoustic waves in a warm plasma

Using the standard reductive perturbation technique,a nonlinear Schroedinger equation is derived to study the modulational instability of finite-amplitude ion-acoustic waves in a non-magnetized warm plasma.It is found that the inclusion of ion temperature in the equation modifies the nature of the ion-acoustic wave stability and the soliton stuctures.The effects of ion plasma temperature on the modulational stability and ion-acoustic wave properties are inestigated in detail.     

Absorption and emission of electron cyclotron waves in plasmas with electron momentum anisotropies both along and across the external magnetic field

Summary A simple and compact form is given to dielectric tensor and ?local emission temperature? for electron cyclotron waves in hot magnetoactive plasmas of thermonuclear interest, containing electron populations with a wide range of possible momentum anisotropies. An analytical model is presented for the representation of electron distributions exhibiting flat suprathermal tails along the external magnetic field and applied to the computation of the pertinent absorption and emission coefficients.     

Head-on collision of quantum ion-acoustic solitary waves in a dense electron-positron-ion plasma

The characteristics of the head-on collision between two-quantum ion-acoustic solitary waves (QIASWs) in a dense electron-positron-ion plasma are investigated. Using the extended Poincaré-Lighthill-Kuo (PLK) method, the Korteweg-de Vries (KdV) equations and the analytical phase shifts, after two QIASWs collision occurs, are derived. This study is a first attempt to illustrate the effects of both of the quantum diffraction corrections and the Fermi temperature ratio of positrons to electrons on the phase shifts. It is found that the electron-positron-ion plasma parameters modify significantly the phase shifts of the two colliding solitary waves.