Genesis of non-uniformity of plasma fluxes over emissive wall in low-temperature plasmas

Abstract

Origins of spatial modulation of stationary electron and ion currents to the wall in discharge plasma with/without magnetic field at low gas pressure are studied in the experiments and 2D PIC MCC simulations. It is shown that a non-uniformity of ion and electron fluxes to the wall is induced by (a) a non-planar topology on the emissive wall, (b) a difference in the secondary electron emission yields of materials in segmented wall or (c) an inclination of the external magnetic field. The transition in the sheath structure over the grooved emissive surface from a developed sheath to a collapsed one caused by the increase of electron energy enlarges the alteration of the ion and electron currents over the grooved or segmented surfaces. The experimental study of the plasma-emissive wall sheath transition was carried out with hexagonal boron nitride wall samples grooved with the characteristic size of 1 mm and 5 mm, which is about of the Debye length. In kinetic simulations, this phenomenon is analyzed in terms of the electron and ion energy distribution functions. An external oblique magnetic field applyed to the dc discharge is found to redistribute the plasma and the periodical structure with the spikes of electron and ion densities forms This phenomena causes the non-uniform spatial distribution of electron and ion currents to the wall. The spikes in electron and ion densities became more pronounced with an increase of magnetic field incidence angle.