On the asymptotic persistence of Langmuir modes in kinematically complex plasma flows

Abstract

The dynamics of Langmuir modes, waves (LW), and shear Langmuir vortices (SLV) are studied in kinematically complex astrophysical plasma flows. It is found that they exhibit several peculiar, velocity shear-induced, asymptotically persistent phenomena, including efficient energy exchange with the background flow and various kinds of instabilities, leading to their exponential growth and echoing solutions with persistent wave-vortex-wave conversions. There is a remarkable similarity between these phenomena and those happening with compressible acoustic modes. The relevance and possible importance of these phenomena for different types of astrophysical plasma flow patterns with kinematic complexity are discussed. In particular, we argue that these physical processes may account for the persistent appearance of plasma oscillations in the heliosphere and interstellar plasma flows. In particular, we believe that the kinematically complex motion of plasma may naturally lead to the asymptotically persistent appearance of Langmuir modes that are born, grown, fed, sustained and maintained by these flows.