HIGHER RADIAL MODES OF AZIMUTHAL SURFACE WAVES ABOVE THE UPPER-HYBRID FREQUENCY IN CYLINDRICAL WAVEGUIDES PARTIALLY FILLED BY PLASMA

Azimuthal surface waves (ASWs) are known to be eigen waves of cylindrical metal waveguides partially filled by magnetoactive plasma. Zeroth radial modes were under study earlier. Their dispersion properties are known to be significantly influenced by the plasma column properties: its particle density, external axial static magnetic field, geometric dimensions, – rather than properties of the dielectric layer which separates the plasma column from the metal wall. Application of higher order ASWs in the low-frequency range was shown earlier to make it possible to get advantage of exciting ASWs with higher frequency than in the case of zeroth order ASWs without no change in the waveguide design. The present study generalises those investigation for the case of the waves above the upperhybrid frequency.

Numerical simulation of a slow extraordinary wave in magnetoactive plasma

Численно и аналитически исследовано влияние внешнего магнитного поля на плоские нерелятивистские нелинейные плазменные колебания. Для инициализации медленной необыкновенной волны в магнитоактивной плазме предложен способ построения недостающих начальных условий на основе решения линейной задачи методом Фурье. С целью численного моделирования нелинейной волны построена схема метода конечных разностей второго порядка точности типа МакКормака на основе эйлеровых переменных. Показано, что при учете внешнего магнитного поля ленгмюровские колебания трансформируются в медленную необыкновенную волну, энергия которой вибрирует при перемещении от начала координат. При этом скорость волны увеличивается с ростом внешнего постоянного поля, что способствует выносу энергии из первоначальной области локализации колебаний. The effect of an external magnetic field on plane non-relativistic nonlinear plasma oscillations is studied numerically and analytically. A method for the initialization a slow extraordinary wave in a magnetoactive plasma is proposed for constructing the missing initial conditions based on solving a linear problem using the Fourier method. For the purpose of numerical simulation of a nonlinear wave, a scheme of the second-order accuracy finite difference method of the MacCormack type based on Euler variables is constructed. It is shown that, when the external magnetic field is taken into account, the Langmuir oscillations are transformed into a slow extraordinary wave whose energy vibrates when moving from the origin. In this case, the wave velocity increases with the growth of the external constant field, which contributes to the removal of energy from the initial region of localization of oscillations.

Effect of obliquely external magnetic field on the intense laser pulse propagating in plasma medium

In this paper, self-focusing of intense laser pulse propagating along the obliquely external magnetic field on the collisional magnetoactive plasma by using the perturbation theory have been studied. The wave equation describing the interaction of intense laser pulse with collisional magnetoactive plasma is derived. In addition, employing source-dependent expansion (SDE) method, the analysis of the laser spot-size is discussed. It is shown that with increasing of the angle in obliquely external magnetic field, the spot-size of laser pulse decreases and as a result laser pulse becomes more focused. Furthermore, it is concluded that the self-focusing quality of the laser pulse has been enhanced due to the presence of obliquely external magnetic field in the collisional magnetoactive plasma. Besides, it is seen that with increasing of [Formula: see text], the laser spot-size reduces and subsequently the self-focusing of the laser pulse in plasma enhances. Moreover, it is found that changing the collision effect in the magnetoactive plasma leads to increases of self-focusing properties.

Longitudinal wave instability due to rotating beam-plasma interaction in weakly turbulent astrophysical plasmas

ABSTRACTThe aim of this study is to highlight the temporal evolution of the longitudinal wave instability due to the interaction between a rotating electron beam and the magnetoactive plasma region in space plasma structures. The plasma structure which could be either in the solar atmosphere or any active plasma region in space is considered weakly turbulent, where the quasi-linear theory is implemented to enable analytic insight on the wave–particle interaction in the course of the event. It is found that in a weakly turbulent plasma, quasi-linear saturation of the longitudinal wave is accompanied by a significant alteration in the distribution function in the resonant region. In case of a pure electrostatic wave, the wave amplitude experiences elevation due to the energy transfer from the plasma particles. This causes flattening of the bump on tail (BOT) in the electron distribution function. If the gradient of the distribution function is positive, the chance that the beam would excite the wave is probable. In such a situation a plateau on the distribution function (∂f/∂v ≈ 0) is formed that will stop the diffusion of beam particles in the velocity space. Evolution of the electron distribution function experiences a decreases of the instability of the longitudinal wave. It is deduced that the growth rate of the wave instability is inversely proportional to the wave energy. Regarding the Sun, in addition to creating micro-turbulence due to wave–particle interaction, as the wave elevates to higher altitudes it enters a saturated energy state before releasing energy that may be a candidate for the generation of radio bursts.