New low-frequency electromagnetic modes associated with neutral dynamics in partially ionised plasma

Abstract. We have investigated the low frequency electromagnetic (EM) modes in inhomogeneous, magnetised partially ionised plasma by incorporating neutral dynamics. We have derived a general EM dispersion relation by using a two-fluids magnetohydrodynamics (MHD) model. Our analysis shows that the neutral dynamics is playing an extremely important role in the physics of magnetised partially ionised plasma by giving rise to new kind of EM modes. We found (1) the new instability is linked with compressibility of neutral particles, the collision between neutral and charged species and the relative streaming in hot/cold, inhomogeneous, magnetised partially ionised plasma, (2) and that neutral dynamics is responsible for the modified (complex) inertial effect on magnetic field lines. Its consequences on the propagation characteristics of Alfvén wave and cyclotron frequency are discussed. Furthermore, a new mode similar to the Langmuir mode is reported. Finally, we discuss our results, for limiting cases, that may be appropriate for applications to space plasma environments including probable mechanism of escaping H⁺ and O⁻ from the Martian atmosphere.