Measurements in a nitrogen plasma boundary layer : the boundary conditions of charged species

The recombination of the major charged species on a metallic wall has been analyzed in a low‐pressure and highly dissociated nitrogen plasma jet. The electron temperature and density in the boundary layer have been measured by electrostatic probes. Information about the temperature and density of some excited species has been deduced from emission spectroscopic measurements. It is shown that the metallic surface is not completely catalytic. The recombination rate has been determined and follows a 0.5 reaction order near the leading edge. The experimental results show that the Bohm criterion overestimates the value of the ion drift velocity at the sheath entrance and confirm the recent value proposed by Zawaideh [Phys. Fluids B 2, 647 (1990)]. At last, a strong enhancement of the N2+(B) emission has been observed near the wall.