Modelling of Sheath Potential Drop Instabilities in Sol with the Use of PR-2 Mirror Machine

The boost and damping of the level of potential fluctuations are reproduced in imitation experiments with an electron beam driven discharge in the linear open system. The most pronounced instability of the sheath potential drop is observed in hydrogen plasmas in the presence of small admixtures of oxygen for materials which form oxides with enhanced emissivity of secondary electrons. Measurements of the plasma fluctuations level are in a qualitative agreement with analytical analysis of temporal evolution of plasma -surface interaction as function of internal and external electric circuit parameters. The surface currents which appear between zones with different emissivity and are closed by the bulk of the incident plasma flow have been studied with the use of the two-plate collector. It is shown that these currents can crucially influence the plasma turbulence.