Dust shedding from a dielectric surface in plasma as a result of charge fluctuations

Abstract

If a body is in a plasma and/or is exposed to streams of charged particles with different signs, or is under UV electromagnetic radiation, etc., then the distribution of the different sign charges on the surface is random. As a result, the surface of the dielectric will be covered by microscopic “spots” with different signs and values of charges, continuously changing in shapes and sizes. A Coulomb force acting on a dust particle lying near the center of such a spot is proportional to the square of the local surface charge density. A stochastic differential equation describing the dynamics of an ensemble of these spots was derived and solved in the article. A solution was obtained also for the dependence of the average spot size, its lifetime, and the standard deviation of the charge density as a function of the plasma species fluxes incident on the surface. It is shown that for normal values of plasma parameters, the Coulomb force repelling a submicron dust particle from a charge spot of somewhat larger size can reach a few tenths of pN, which is comparable to the value of the adhesive van der Waals force that holds dust particles on the surface. The possibility of improving the cleaning efficiency with changes in surface treatment conditions is analyzed as well.