The concentration of argon and nitrogen are measured by gas chromatography for an inductively coupled plasma discharge in argon which is surrounded by a nitrogen sheath. The mixing of nitrogen with the argon discharge is substantially different than cold-gas mixing when no discharge is present. The formation of a toroidal discharge with a central flow further decreases the mixing of nitrogen with the discharge. More than a few percent nitrogen mixed into the argon discharge drastically alters the plasma temperature distribution.
Ramon M. Barnes and Seifollah Nikdel, "Mixing of Ambient Nitrogen in a Flowing Argon Inductively Coupled Plasma Discharge," Appl. Spectrosc. 29, 477-481 (1975)