STUDIES OF ALFVEN AND LOWER HYBRID WAVES IN PLASMA AND COMPLEX PLASMA

Abstract

The excitation of waves, may be electromagnetic or electrostatic, in plasmas or dusty plasmas by electron or ion beams (relativistic or non-relativistic) has also attracted considerable attention. Beam-plasma interaction involves many physical aspects, including, for example, mechanisms of wave radiation, collective processes leading to instabilities, plasma and beam dynamics, as well as several applications, such as communications between two spacecraft or between spacecraft and the earth. An electron mode depends on the mass of the electrons, but the ions may be assumed to be infinitely massive, i.e., stationary while an ion mode depends on the ion mass, but the electrons are assumed to be massless and redistribute themselves instantaneously according to Boltzmann relation. Only rarely, for example, in the lower hybrid oscillation, will a mode depend on both the electron and the ion mass. The various wave modes can also be classified according to whether they propagate in an un-magnetized plasma or parallel, perpendicular, or oblique to the static magnetic field. Moreover, the presence of highly charged dust particles in a plasma can have significant influence on the collective properties of the plasma, and hence wave mode properties. The waves and instabilities can be excited either by the free sources of energy such as plasma currents produced by the electromagnetic and electrostatic fields present within the plasma or by an external beam source propagating inside it. Hence, we aim at the theoretical investigations of waves and instabilities in plasmas or dusty plasmas. We have studied, analytically, abnormal Doppler resonance with an electron beam in a magnetized plasma that causes a plane polarized Alfven wave to decay nonlinearly. There are two different wave propagation modes namely, the Alfven wave mode, with a frequency lesser than plasma ion frequency ωci and the electron cyclotron wave mode, with a frequency approaching electron cyclotron frequency ωce. The plane polarized Alfven waves and electron beam communicate through both normal and abnormal Doppler resonance. The frequency does not fluctuate and the wave stabilizes in anomalous resonance contact in contrast to the case of normal Doppler resonance. It is also described in this work, how the frequency and growth rate of plasma electrons vary with magnetic field and number density. Rajesh Gupta Delhi Technological University, Delhi, India The Shear Alfven waves are only affected by the beam's particles when they counter propagate one-another and destabilize left-hand polarized modes for parallel waves and left hand as well as right-hand polarized modes for oblique waves via an action called fast cyclotron interaction. Right-hand (RH) and left-hand (LH) polarized oblique Alfven modes are affected differentially by collisions between beam ions and plasma constituents in terms of the growth rate and frequency of produced Alfven waves. We have also observed that the polarized oblique Alfven modes exhibit a polarization reversal after resonance. The growth rates are correlated with the increase in propagation angle and because of the obliquity of the wave, the maximum growth rate rises in the presence or absence of the beam. The frequency and growth rate of the waves both are affected by the collision of beam ions with plasma constituents. As the beam velocity drops, the significance of collisions increases and they damp the Alfven waves more and more. We have also given a theoretical analysis on the generation of an obliquely propagating shear Alfven wave in dusty plasma by hydrogen ion beam. When the ion beam particles counter-propagate with a shear Alfven wave, they interact with through cyclotron interaction with the wave whereas through Cerenkov interaction with a co-propagating wave. It has been discussed about how the beam speed, magnetic field, wave number, dust particle density, and dust charge fluctuations affect the situation. As the beam velocity increases, both the wave frequency and maximum growth rate decrease, with the changes being different for parallel and perpendicular wave numbers. The findings and experimental observations are well congruent. A problem based on fluid theory of beam driven growth of lower hybrid wave (LHW) in a magnetized relativistic beam plasma system is also has been studied. The decay of large amplitude lower hybrid wave, the pump or mother wave into lower-hybrid sideband wave and beam mode drives the instability. A ponderomotive force is applied to plasma electrons by the excited sideband wave when it interacts with the pump wave. The dependence of parametric instabilities on the local plasma characteristics has been used to determine the rate of growth of the beam driven instability in various beam density regions. The results indicate that electron dynamics in the presence of a relativistic electron beam play a major role in the beam coupling those results in parametric instability of the LH wave. Rajesh Gupta Delhi Technological University, Delhi, India The present research work can be extended to study waves and instabilities in plasmas and findings of the present research work may be useful in investigating astrophysical situations, near earth environment, and fusion plasma devices, etc.