Dispersion relations and polarizations of low-frequency waves in two-fluid plasmas
Abstract
Analytical expressions for the dispersion relations and polarizations of low-frequency waves in magnetized plasmas based on two-fluid model are obtained. The properties of waves propagating at different angles (to the ambient magnetic field B0 ) and β (the ratio of the plasma to magnetic pressures) values are investigated. It is shown that two linearly polarized waves—namely, the fast and Alfvén modes in the low- β (β≪1 ) plasmas, the fast and slow modes in the β∼1 plasmas, and the Alfvén and slow modes in the high- β (β≫1 ) plasmas—become circularly polarized at the near-parallel (to B0 ) propagation. The negative magnetic-helicity of the Alfvén mode occurs only at small or moderate angles in the low-β plasmas, and the ion cross-helicity of the slow mode is nearly the same as that of the Alfvén mode in the high-β plasmas. It is also shown that the electric polarization δEz/δEy decreases with the temperature ratio Te/Ti for the long-wavelength waves, and the transition between left- and right-hand polarizations of the Alfvén mode in Te/Ti≠0 plasmas can disappear when Te/Ti=0 . The approximate dispersion relations in the near-perpendicular propagation, low-β, and high-β limits can quite accurately describe the three modes.
- Publication:
-
Physics of Plasmas
- Pub Date:
- April 2015
- DOI:
- 10.1063/1.4919257
- arXiv:
- arXiv:1505.07595
- Bibcode:
- 2015PhPl...22d2115Z
- Keywords:
-
- Physics - Plasma Physics;
- Physics - Space Physics
- E-Print:
- 16 pages, 6 figures. Code for figure 2 is included