Observation of a significant drop of electron density in cascaded arc argon plasma doped with oxygen gas using laser Thomson scattering

Abstract

In this work, the electron density (n e) and electron temperature (T e) of cascaded arc argon plasma regulated by adding electronegative oxygen gas have been investigated using laser Thomson scattering diagnostic technique. The results indicate that the addition of O2 gas causes a significant decrease of n e, which drops from 1020 m−3 to 1017 m−3. This is mainly attributed to the dissociative recombination reaction between electrons and O2 + molecular ions. Meanwhile, the formation of negative ions, O2 − and O−, consumes electrons and further makes n e decrease. But, T e remains nearly unchanged with the increase of O2 ratio from 0% to 10%. This is probably due to that the electron energy loss by the electron collisions with O2 molecules in the ground state balances the electron heating induced by the super-elastic collisions with the highly vibrational excited O2 molecules.