Multiple species plasma boundary criterion with non-degenerate entry flows

Abstract

The structure and spatial scaling of a collective electrostatic sheath forming in multiple-ion-species plasmas flowing into an absorbing boundary is examined using generalized criterion allowing non-degenerate entry flows. The sheath thickness is characterized with respect to the relative velocities of entry between individual ion species. Using the dispersion relation of multiple ion species plasma it is shown that while the smaller sheath thickness corresponds to the entry velocities of the incident ion species far exceeding the effective ion acoustic velocity. The plasma Debye length remains the limiting value of the sheath thickness beyond which the entry velocity solutions are lost as the individual ion velocities must ideally approach infinity for the sheath dimension approaching the Debye length.