A study of SCL sheath in presence of two dust species in a photoemissive environment

Abstract

We have presented a basic model for a one dimensional collisionless space charge limited (SCL) plasma sheath consisting of electrons, ions, and two kinds of dust populations—a nano-dust population and a micrometer sized dust population. We have assumed that the nano-dust particles, plasma electrons, photoelectrons, and ions are the constituents of the plasma fluid and the micrometer sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics. We have assumed that the charges of the micrometer-dusts are determined from the current balance on them and the charges on the nano-dusts are fixed. Due to photoemission, like the lunar surface charges to a positive potential, so the nano-dust and micrometer-dust particles charge to a positive potential. The electron densities have been derived by assuming both the electrons and photoelectrons to be Maxwellian, whereas the ion and nano-dust densities are derived from energy conservation of the ions and nano-dust particles and the continuity equations. Being a constituent of plasma, the nano-dusts do affect the sheath dynamics through the Poisson equation, which determines the plasma potential in the sheath region. The typical conditions for the levitation of dust particles in an SCL sheath including the maximum height and maximum size of the particles are calculated.