THEORETICAL INVESTIGATIONS OF WAVES AND INSTABILITIES IN DUSTY AND STRONGLY COUPLED DUSTY PLASMAS

Abstract

Dusty plasmas are characterized by the presence of micron to sub-micron sized dust particles immersed in partially or fully ionized plasma. It can be produced by dispersing dust grains into a plasma (Q-machine) or by growing dust in the plasma of certain chemically reactive gases like Silane (SiH4) and Oxygen (O2). Various processes like interaction of dust grains with gaseous plasma particles, energetic particles (electrons and ions), photons, secondary electron emission, thermionic emission, and photoelectric emission are responsible for charging of dust grains in a plasma. These dust grains in plasmas acquire a high negative charge and the presence of these highly charged dust particles in a plasma can have significant influence on the collective properties of the plasma. Dusty plasmas are widespread in astrophysical situations like planetary rings, comet tails, and interstellar clouds. In plasma processing reactors, dust particles grow from gaseous molecules to nano-meter sized particles. The removal of these plasmagrown dust particles is a crucial problem in computer chip manufacturing industry. In contrast, novel materials, such as solar cells with highly improved efficiency, can be manufactured from thin films by incorporating the dust particles. An interesting property of dusty plasmas is that the dust particles can arrange themselves into ordered structures, so-called plasma crystals which are a consequence of strong coupling among dust grains. The study of strongly coupled plasmas also has great potential due to their vast applications in astrophysical plasmas such as interplanetary medium, white dwarf matter etc. and laboratory plasmas such as laser produced plasmas, and plasma crystals. Moreover, strongly coupled dusty plasmas have received profound attention because of (i) their ability to form “Coulomb Crystals” and (ii) the excitation of the dust acoustic (DA) and dust lattice (DL) waves. The studies of waves and instabilities in dusty as well as strongly coupled dusty plasmas have also received great attention in past few years. Moreover, it is a well known fact that the waves and instabilities can be excited either by the free sources of energy such as plasma currents produced by the electrostatic and electromagnetic fields present within the plasma or by external beam sources propagating inside it. Hence, we aim at the theoretical investigations of waves and instabilities in dusty plasmas.

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Moreover, we extend our investigations to observe the low frequency modes in strongly coupled dusty plasmas as well. A theoretical model to elucidate the excitation of an ion beam driven ion acoustic waves (IAWs) in a plasma cylinder having negatively charged dust grains have been developed. The first order perturbation technique has been used to evaluate the growth rate of instability. The destabilizing effect of relative concentration of negatively charged dust on the frequency and the growth rate, and phase velocity of ion beam driven ion acoustic instability has been observed. It has been found that electrostatic ion-acoustic waves are driven unstable in a magnetized dusty plasma cylinder through an ion beam via Cerenkov interaction. Moreover, the beam parameters such as density and energy play a significant role in enhancing the real frequency and the growth rate of the IAW modes. It has also been observed that the dust charge fluctuations play an important role in suppression of the current driven electrostatic ion-cyclotron waves in a magnetized collisional dusty plasma. Kelvin Helmholtz instability in a magnetized dusty plasma can be driven by an ion beam via Cerenkov interaction. Unstable KHI modes frequencies and axial wave vectors increase with the relative density of negatively charged dust grains δ in the presence of beam. The KHI mode frequency is enhanced in the presence of dust charge fluctuations while dust charge fluctuations play a significant role in damping of the KH- instability modes. A comparison of frequency and the growth rate for finite and infinite geometry of plasma waveguide shows a reduction in both frequency and the growth rate for finite geometry. Moreover, the radial boundaries also affect the dispersion properties of the KHI modes. The Kelvin Helmholtz instability in a magnetized plasma having negative ions can also be driven by an ion beam via a Cerenkov interaction. The KHI mode frequencies and axial wave numbers of the both positive ions and negative ions increase with the relative density of negative ions ε in the presence of beam. The presence of beam and its various parameters significantly modify the growth rate of both the KHI ion modes. Moreover, the stabilizing effect of relative mass of positive and negative ions has also been observed. It has been observed that the presence of

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negative ions destabilizes the KHI modes which can find applications in surface plasma technologies. Low frequency longitudinal and transverse modes driven by magnetic field aligned current drifts in a magnetized strongly coupled collisional dusty plasma have been theoretically investigated. Longitudinal modes contain ion dust hybrid modes while transverse mode is similar to an elastic wave. The theoretical models which are based on generalized hydrodynamic approach have been developed for hydrodynamic and strongly coupled kinetic regime for the local and nonlocal plasmas, respectively. The strong correlation parameter is found to have a stabilizing effect on current driven longitudinal modes due to increase in viscous damping while for transverse modes the effect of viscous damping is weak due to restoring force provided by elastic effects. The present research work can be extended to study waves and instabilities in non-linear regimes of plasmas and findings of the present research work may be useful in investigating astrophysical situations, near earth environment, and fusion plasma devices, etc.