Ion collection by a sphere in a flowing highly collisional plasma

Ion collection by a small negatively biased sphere in flowing highly collisional plasmas is investigated. Ion trajectories in the vicinity of the sphere are obtained from the solution of the ion equation of motion. From the analysis of the trajectories, the total ion flux to the sphere is determined and the sphere floating potential is calculated from the balance between ion and electron fluxes. The asymmetry in ion collection by the upstream and downstream sides of the sphere is quantified. The results obtained can be important in the context of complex (dusty) plasmas, as well as in the context of probe theory