Kinetic features of collisionless sheaths around polarized cylindrical emitters from the orbital motion theory

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2017-10
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AIP Publishing
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Abstract
The kinetic features of the sheath around a cylindrical emitter immersed in collisionless plasma at rest are analysed. After finding self-consistently the electric potential by applying the Orbital Motion Theory to the Vlasov-Poisson system, the local distribution functions are reconstructed and the radial profiles of important macroscopic quantities (plasma densities, currents, and temperatures) are then computed. It is found that there can only be three kinds of holes that are bound by three different boundaries-two related to the constraints from orbital effects and the other due to the electric potential barrier. The results are presented for three regimes: negative probe bias with monotonic and non-monotonic potential and positive probe bias with non-monotonic potential. To understand the variation of macroscopic-quantity radial profiles, three diagrams are presented for kinetic features: the epsilon l-diagram for the integration domains of the two orbital invariants, the effective potential, and the local distribution function. The envelope in the epsilon l-diagram is crucial to identify different orbital behaviours, which can be used as a guideline for analytical analyses and serve as one of the criteria to refine the mesh used in numerical calculations. Published by AIP Publishing.
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