Study of sheath induced nonlinear phenomena in laboratory plasmas

Abstract

In this thesis, a study has been made to investigate the sheath induced nonlinear phenomena in laboratory plasmas. The production of sheath is a natural consequence in any plasma system. An external ion sheath is formed by applying negative potential, which must be greater than electron temperature (Te), if the sheath is produced around an electrode immersed in plasma. In this study a steady state ion sheath is formed by biasing the mesh grid negatively with respect to the ground in a double plasma device. A strong electric field will be produced inside the sheath in order to maintain the quasinuetrality condition of the bulk plasma. The aim of this study is to study the nonlinear phenomena due to the effect of ion sheath in a double plasma device and in an electron cyclotron resonance plasma source. The sheath in the double plasma device is non-magnetised, weak and collision free. In this thesis, the experimental investigations of some phenomena resulting from the nonlinear state of waves and instabilities in plasmas in presence of sheath have been studied. The whole study have been made in two component Ar plasma as well as in multicomponent plasma with negative ions by injecting SF6 gas into the chamber of Ar plasma. The different experimental results are compared with the existing theory and experiment wherever required. The study of sheath phenomena is getting a growing interest among the plasma physicist because of its large scale applications. The complete set of experiment is performed in a double plasma device and in an electron cyclotron resonance plasma system. The experimental setup of the two system and its necessary diagnostics are described in the chapter II of this thesis. The four diagnostics (Langmuir probe, Emissive probe, Ion energy analyser and Faraday Cup) are used in the whole work of this thesis. The dispersion relation is observed with the help of interferometer method in order to observe the beam and ion acoustic mode in plasma simultaneously. The emissive probe is particularly...