Electrostatic solitons and Alfvén waves generated by streaming instability in electron-positron plasmas

Electron-positron plasmas may be present in laboratory experiments and certain astrophysical environments. Due to the inertia symmetry there have been some debates about whether the nonlinear electrostatic solitons generated easily in electron-proton plasmas may develop in electron-positron plasmas. In this study we show the formation of electrostatic solitons and electromagnetic Alfvén waves in extensive magnetized electron-positron plasma system generated by streaming instabilities based on electromagnetic particle simulations along with fluid theory analyses. In particular, the four-component beam-plasma system may lead to the formation of interlacing electron and positron solitons in the early evolution stage (say, t<20ωp-1, where ωp is the plasma frequency) and large-amplitude Alfvén waves in the later phase (say, t>150ωp-1). The magnetic-field perturbations are generated by the beam and firehose-type instabilities associated with temperature anisotropy of T >T resulting from the parallel plasma heating by the electrostatic instability. It is shown that the growth rates and the dominant wavelengths of both electrostatic and electromagnetic instabilities are consistent with the fluid theory. The coexistence of electrostatic solitons and electromagnetic Alfvén waves with significant magnetic field fluctuations in the same system is a unique feature of electron-positron plasmas and the unified theory behind the formation mechanisms is well addressed in the paper.