VELOCITY SHEAR GENERATED ALFVEN WAVES IN ELECTRON-POSITRON PLASMAS

Linear magnetohydrodynamic (MHD) modes in a cold, nonrelativistic elec tron-positron plasma shear flow are considered. The general set of dif ferential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfven perturbatio ns may exhibit large transient growth fueled by the mean kinetic energ y of the shear flow, The velocity shear also induces mode coupling, al lowing the exchange of energy as well as the possibility of a strong m utual transformation of these modes into each other. The compressional Alfven mode may extract the energy of the mean flow and transfer it t o the shear Alfven mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e (+)e(-) plasmas in emphasized. It is speculated that the shear-induced effects of the electron-positron plasmas could also help solve some a strophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasmas are relativistic, it is shown that th e major results of the study remain valid for weakly shared relativist ic plasma. (C) 1996 American Institute of Physic s.