The Floating Potential of Emitting Plasma Probes

Abstract

The floating potential of a probe in a high density seeded plasma is described with the classical electrostatic probe theory extended to include emission. In general, this emission consists of ions, atoms, and electrons. The rate at which these particles are emitted depends on the probe tempera- ture and on its surface coverage by the seed. Since the ion arrival is gov- erned by how the surface floats electrically with respect to the plasma, a coupled situation can exist. The problem in formulated in terms of two-temperature description where plasma electrons retain their temperature as they approach the surface. The theory is developed in general for probes biased to a surface where emission conditions can be known, and then it is specialized to catalytic and noncatalytic surfaces. The noncatalytic situation is correlated with some data for an atmospheric argon plasma seeded with potassium. A computational scheme is used to calculate the equilibrium fluxes from a surface which is absorbing seed.