Current flow and pair creation at low altitude in rotation-powered pulsars’ force-free magnetospheres: space charge limited flow

Received; in original form We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of Rotation Powered Pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, includ-ing a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte-Carlo treatment of the high energy gamma rays that mediate the formation of the electron-positron pairs. We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially 1D, designed to explore the physics, although of practical relevance to young, high voltage pulsars. We observe novel behavior. a) When the current density j is less than the Goldreich-

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