A kinetic theory of ion collection by probe in flowing unmagnetized plasma

A one-dimensional kinetic model is developed for the flow of ions to a probe whose characteristic size is smaller than the ion gyroradius in drifting plasmas. Numerical solutions of the self-consistent plasma-sheath equations have been obtained for arbitrary external temperature and parallel plasma flow velocity. The ion current to the probe is obtained and the ratio of the upstream to downstream current is represented by the form R=exp[KU_d], where U_d is the drift velocity in units of (T_e/m_i)^0.5 and K is constant depending on the type of source in the sheath-transition region. Comparisons with other models are made.