Linear and Non-linear waves in Multispecies Plasmas

Abstract

Space and laboratory plasmas are inherently multispecies with electrons, two or more positive and/or negative ion species, and possibly charged dust species. Nonthermal particle distributions have also been observed in many space, and astrophysical environments. In this thesis, we have investigated the propagation of the fast and slow ion acoustic modes in a negative ion plasma with heavier and cooler positiveionspeciesandkappadistributedelectrons,andthepropagationofthedust ion acoustic wave in a dusty plasma with a positively charged dust and Cairns distributed electrons. When the temperature of ion species is very small compare to the electron temperature, the fast mode in a negative ion plasma supports the propagation of both compressive and rarefactive solitons, and there exist a range of plasma parameter values in which the two types of structures coexist. When the ion temperature effects are important, it supports only rarefactive solitons and this effect is enhanced by the superthermal behavior of the electrons. If electrons are strongly nonthermal, theslowmodesupportsnormalcompressivesolitons,supersolitonsanddoublelayers for high values of the negative ion density. The double layers occur under two different identities, first as the lower limit to the supersoliton existence range and, second, as the limiting factor for the propagation of normal solitons. A dusty plasma with positively charged dust and strongly nonthermal electrons supportsthecoexistence ofKdV(nonKdV)compressivesolitonslimitedbytheoccurrence of the ion sonic point and nonKdV (KdV) rarefactive solitons limited by the occurrence of double layers. At a critical dust-to-ion density ratio, compres v sive and rarefactive solitons coexist without a soliton with finite amplitude at the acousticspeed,contrarytoearlierstudies. Thissuggeststhattheexistenceofasoliton with finite amplitude at the acoustic speed is not always a pre-requisite for the coexistence of nonlinear structures of both polarities.