A two-fluid analysis of waves in a warm ion–electron plasma
Published in Physics of Plasmas, 2020
Abstract. Following recent work, we discuss waves in a warm ideal two-fluid plasma consisting of electrons and ions starting from a completely general, ideal two-fluid dispersion relation. The plasma is characterized by five variables: the electron and ion magnetizations, the squared electron and ion sound speeds, and a parameter describing the angle between the propagation vector and the magnetic field. The dispersion relation describes six pairs of waves which we label S, A, F, M, O, and X. Varying the angle, it is argued that parallel and perpendicular propagation (with respect to the magnetic field) exhibit unique behavior. This behavior is characterized by the crossing of wave modes which is prohibited at oblique angles. We identify up to six different parameter regimes where a varying number of exact mode crossings in the special parallel or perpendicular orientations can occur. We point out how any ion–electron plasma has a critical magnetization (or electron cyclotron frequency) at which the cutoff ordering changes, leading to different crossing behaviors. These are relevant for exotic plasma conditions found in pulsar and magnetar environments. Our discussion is fully consistent with ideal relativistic MHD and contains light waves. Additionally, by exploiting the general nature of the dispersion relation, phase and group speed diagrams can be computed at arbitrary wavelengths for any parameter regime. Finally, we recover earlier approximate dispersion relations that focus on low-frequency limits and make direct correspondences with some selected kinetic theory results.
Preprint - arXiv:2011.06282
Erratum. In Fig. 5b, the electron densities of the data points for Pulsar Wind and Magnetar Wind are a factor of \(10^3\) too small and should be shifted to the right accordingly. The discussion is unaffected.
Recommended citation: De Jonghe, J. and Keppens, R. (2020). "A two-fluid analysis of waves in a warm ion–electron plasma." Phys. Plasmas. 27(12), 122107. http://doi.org/10.1063/5.0029534