Sounds like contained water. Am I wrong? Water is very dangerous in some phases. With respect, Sir.
There are plasmas at low pressure. The method sections of the paper talks about it. The water provides the fuel and the catalyst.
Water vapor was generated by pumping on a reservoir(about 20 cc) of distilled, de-ionized water. The flow rate wasnot directly controlled, but rather a needle valve was adjustedto maintain the desired pressure, as measured by a MKSbaratron placed above the Welch two stage rotary vane oilsealed vacuum pump (Model 8920) with a rated capacity of218 l min1. This pump was attached to the chamber with a1 cm ID ultratorr fitting at the end opposite that at which gasentered. The entire system, except the spectrometer wasencased in a copper screen Faraday cage