Plasma collisions at mildly relativistic speeds : Formation of an electrostatic turbulent boundary layer

• Plasmas collide at relativistic speeds in many astrophysical and high energy density laboratory environments. The collision boundaries are not well understood. In the absence of a magnetic field B0 that is parallel to the flow velocity vector vb the boundaries are filamentary, since waves grow with wavevectors k that are not parallel to vb. Modelling such boundaries requires large 3D particle-in-cell (PIC) simulations. A flow-aligned B0 can suppress wave modes other than k parallel to vb, as multi-dimensional PIC simulations show. We select a vb, a plasma temperature T and B0, for which the growth rate of the two-stream instability exceeds that of all other instabilities. We exploit this planarity to resort to a 1D simulation, that lets two identical electron-proton plasma slabs collide with a relativistic speed and a Mach number of over 400. The developing electrostatic turbulent boundary dissipates its energy via electron phase space holes that accelerate electrons to relativistic speeds and increase significantly the speed of some protons. The results are important in the context of a dynamic accretion disc and microquasar jets. The accelerated electrons may feed the disc wind and the relativistic leptonic jets, and possibly contribute to the hard radiation component of the accretion disc.

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plasma physics

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