LINEAR AND NONLINEAR DYNAMICS OF NONUNIFORN ELECTRON POSITRON ION PLASMAS

The dynamics of low frequency electrostatic and electromagnetic drift waves in collisionless nonuniform magnetized electron-positron-ion (e-p-i) plasmas is studied. It is found that the drift wave frequency can be very low in such plasmas depending upon the concentration of different plasma species. The Hasegawa-Mima equation is modified. The solutions of the nonlinear equations are obtained in the form of vortices in both electrostatic and electromagnetic limits.The two dimensional large amplitude ion acoustic waves can give rise to dipolar vortex structures in magnetized homogeneous e-p-i plasmas as well. It is shown that in nonuniform plasmas the acoustic mode can couple with electrostatic drift waves and vortex-like nonlinear structures can be produced.A set of nonlinear equations is derived which describe the coupling of ion acoustic wave, Alfven wave and drift wave. These equations also give the stationary solution in the form of dipolar vortices. Linear dispersion relation of several coupled electrostatic and electromagnetic low frequency modes is also obtained.Linear and nonlinear Alfven waves are also studied in the presence of a background current gradient in e-p-i plasmas. The instability criterion becomes dependent upon the concentration of different species in a three component plasma.It is also pointed out that the drift waves can become unstable due to shear flow produced by externally applied electric field. The modified Rayleigh instability condition is obtained which is applicable to both electron-ion and e-p-i plasmas. It is proposed that the shear flow driven drift waves can be responsible for large amplitude electrostatic fluctuations in tokamak edges. A particular form of the shear flow can give rise to counter rotating vortices and vortex chains. A comparison of this work with the limiting cases of electron-ion and electron positron plasmas is also presented. It is pointed out that this investigation can be applicable to both astrophysical and laboratory plasmas