Electromagnetic solitary pulses in a magnetized electron-positron plasma

A theory for large amplitude compressional electromagnetic solitary pulses in a magnetized electron-positron ($e$-$p$) plasma is presented. The pulses, which propagate perpendicular to the external magnetic field, are associated with the compression of the plasma density and the wave magnetic field. Here the solitary wave magnetic field pressure provides the restoring force, while the inertia comes from the equal mass electrons and positrons. The solitary pulses are formed due to a balance between the compressional wave dispersion arising from the curl of the inertial forces in Faraday's law and the nonlinearities associated with the divergence of the electron and positron fluxes, the nonlinear Lorentz forces, the advection of the $e$-$p$ fluids, and the nonlinear plasma current densities. The compressional solitary pulses can exist in a well-defined speed range above the Alfvén speed. They can be associated with localized electromagnetic field excitations in magnetized laboratory and space plasmas composed of electrons and positrons.

Figure 1

The spatial profiles of the normalized magnetic field $B$ (top panel) and the plasma density $n$ (bottom panel) for $\beta =0$ and Mach numbers $M=1.2$ (dashed curves) and $M=1.5$ (solid curves). The amplitude decreases for finite $\beta$, for example, for $\beta =0.1$ and $M=1.2$ (dotted curves).