Generation of superthermal electrons by electron beams

A series of computer simulations is reported studying the coupling of a continuously injected cold electron beam into a warm background plasma. The simulations are performed in a finite length nonperiodic system. It is shown that strong turbulence determines the coupling of the beam to the ambient plasma and leads to the formation of superthermal electrons with velocities comparable to that of the injected beam. These electrons are accelerated both in the direction of the beam and back toward the gun. The superthermal electrons can carry return currents greater than the beam current. For active beam injection experiments in space, these particles provide a direct indication of the presence of the beam plasma interaction.

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