Large-amplitude electromagnetic waves in magnetized relativistic plasmas with temperature

Abstract

Abstract. Propagation of large-amplitude waves in plasmas is subject to several sources of nonlinearity due to relativistic effects, either when particle quiver velocities in the wave field are large, or when thermal velocities are large due to relativistic temperatures. Wave propagation in these conditions has been studied for decades, due to its interest in several contexts such as pulsar emission models, laser-plasma interaction, and extragalactic jets.For large-amplitude circularly polarized waves propagating along a constant magnetic field, an exact solution of the fluid equations can be found for relativistic temperatures. Relativistic thermal effects produce: (a) a decrease in the effective plasma frequency (thus, waves in the electromagnetic branch can propagate for lower frequencies than in the cold case); and (b) a decrease in the upper frequency cutoff for the Alfvén branch (thus, Alfvén waves are confined to a frequency range that is narrower than in the cold case). It is also found that the Alfvén speed decreases with temperature, being zero for infinite temperature.We have also studied the same system, but based on the relativistic Vlasov equation, to include thermal effects along the direction of propagation. It turns out that kinetic and fluid results are qualitatively consistent, with several quantitative differences. Regarding the electromagnetic branch, the effective plasma frequency is always larger in the kinetic model. Thus, kinetic effects reduce the transparency of the plasma. As to the Alfvén branch, there is a critical, nonzero value of the temperature at which the Alfvén speed is zero. For temperatures above this critical value, the Alfvén branch is suppressed; however, if the background magnetic field increases, then Alfvén waves can propagate for larger temperatures.There are at least two ways in which the above results can be improved. First, nonlinear decays of the electromagnetic wave have been neglected; second, the kinetic treatment considers thermal effects only along the direction of propagation. We have approached the first subject by studying the parametric decays of the exact wave solution found in the context of fluid theory. The dispersion relation of the decays has been solved, showing several resonant and nonresonant instabilities whose dependence on the wave amplitude and plasma temperature has been studied systematically. Regarding the second subject, we are currently performing numerical 1-D particle in cell simulations, a work that is still in progress, although preliminary results are consistent with the analytical ones.

Modification of magnetohydrodynamic waves by the relativistic Hall effect

“…Keppens and Meliani drew phase and group diagrams of the relativistic MHD showing that there is no qualitative difference between non-relativistic and relativistic diagrams in a fluid rest frame, except for the presence of the light limit [27]. In addition to the relativistic MHD, * yohei.kawazura@physics.ox.ac.uk there are studies on wave properties for relativistic electronpositron pair plasma [28][29][30]. For relativistic electron-ion plasma, whereas the dispersion relation for the relativistic XMHD was derived by Koide [19] in specific wave vector configurations, a general dispersion relation in any wave vector direction has not been formulated.…”

Waves propagating parallel to the magnetic field in relativistically hot plasmas: A hydrodynamic model with the average reverse gamma factor evolution

“…A large number of wave phenomena in the electron-positron plasmas with the large temperatures has been studied in ref. [25], in which the large-amplitude circularly polarized waves propagating along a constant magnetic field are considered. The analysis presented in ref.…”

“…The analysis presented in ref. [25] is based on both kinetic equations and hydrodynamics composed of a four‐momentum evolution equation. In the presented hydrodynamics the four‐momentum is represented via the four‐velocity via the temperature‐dependent parameter $$$ f $$$ (see Equation 3).…”

Large-amplitude circularly polarized electromagnetic waves in magnetized plasma

“…13,14 Models of circularly polarized waves in electron-positron plasmas have a wide range of applicability. [15][16][17] Parametric instabilities of such waves have been considered as a source of particle acceleration in pulsar magnetospheres. [18][19][20] One of the first models of LACP waves has been developed in Ref.…”