An interpolation formula for the ion flux to a small particle in collisional plasmas

Ion collisionality is known to be a major factor which determines the magnitude of the surface (floating) potential of an individual particle immersed in a plasma. In this paper a simple interpolation formula for the ion flux collected by such a particle in the entire range of ion collisionality is proposed. The dependency of the floating potential on ion collisionality calculated using this formula as well as using other analytic approximations developed recently are compared. The reliability of different approaches is discussed.