Transonic plasma flow past an obstacle

In many plasmas the ions are cold relative to the electrons but have a directed, subsonic velocity (the sonic velocity is (kT_e/M)½). The behaviour of this flow around an obstacle is considered and solutions obtained for cylindrical geometry. The results are of direct interest in the interpretation of probe characteristics, especially when relative density measurements are involved, as the effects of the flow are typically of the same order of magnitude as the relative variations expected. Plasma flow past an obstacle may be of interest in other contexts (e.g. the case of dust particles in a gas discharge).