  The post-discharge of an RF plasma torch supplied with helium and oxygen
gases is characterized by mass spectrometry, optical emission spectroscopy and
electrical measurements. We have proved the existence of a dc current in the
post-discharge (1--20 A), attributed to the Penning ionization of atmospheric
nitrogen and oxygenated species. The mechanisms ruling this dc current are
investigated through experiments in which we discuss the influence of the O2
flow rate, the He flow rate and the distance separating the plasma torch from a
material surface located downstream.
