Proton acceleration in plasma turbulence driven by high-energy lepton jets

Abstract The interaction of high energy lepton jets composed of electrons and positrons with background electron–proton plasma is investigated numerically based upon particle-in-cell simulation, focusing on the acceleration processes of background protons due to the development of electromagnetic turbulence. Such interaction may be found in the universe when energetic lepton jets propagate in the interstellar media. When such a jet is injected into the background plasma, the Weibel instability is excited quickly, which leads to the development of plasma turbulence into the nonlinear stage. The turbulent electric and magnetic fields accelerate plasma particles via the Fermi II type acceleration, where the maximum energy of both electrons and protons can be accelerated to much higher than that of the incident jet particles. Because of background plasma acceleration, a collisionless electrostatic shock wave is formed, where some pre-accelerated protons are further accelerated when passing through the shock wave front. Dependence of proton acceleration on the beam-plasma density ratio and beam energy is investigated. For a given background plasma density, the maximum proton energy generally increases both with the density and kinetic energy of the injected jet. Moreover, for a homogeneous background plasma, the proton acceleration via both turbulent fields and collisionless shocks is found to be significant. In the case of an inhomogeneous plasma, the proton acceleration in the plasma turbulence is dominant. Our studies illustrate a scenario where protons from background plasma can be accelerated successively by the turbulent fields and collisionless shocks.