Driven waves in a two-fluid plasma

Abstract

We study the physics of wave propagation in a weakly ionised plasma, as it applies to the formation of multifluid, MHD shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time scales, ambipolar diffusion on long time scales, and transitional behavior at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward- and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force free motion and the magnetic field grows monotonically with time. The flow appears to be self similar at the time when linear analysis ceases to be valid.

18 pages including 24 figures, accepted by MNRAS

References in corpus (9)

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Cited by in corpus (8)

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• Ambipolar Diffusion in Action: Transient C shock Structure and Prestellar Core Formation
• A Two-Fluid Method for Ambipolar Diffusion
• Time-dependent simulations of steady C-type shocks
• On the Alfven wave cut-off in partly ionized collisional plasmas
• On the propagation of Alfvén waves in the dusty interstellar medium. Can we neglect dust inertia in molecular clouds?
• Molecular Line Emission from Multifluid Shock Waves. I. Numerical Methods and Benchmark Tests