Low-Pressure HF Jet Discharge in a System with a Liquid (Non-Metallic) Electrode

A high-frequency jet discharge (1.76 MHz) at reduced pressure in a system with a liquid plasma-forming medium (6% aqueous solution of (NH4)2SO4) has been studied experimentally. The morphology and stability of the discharge, its electrophysical, spectral, and thermal characteristics have been studied in the range of 1000–80 000 Pa. It is shown that the discharge transferred from a discrete microchannel structure to an extended truncated-conical column when the pressure decreased from close to atmospheric one to 20‒4 kPa. At ~1 kPa, non-stationarity and breakdown dynamics occur due to a decrease in the boiling point and intense vaporization. The current–voltage characteristics are plotted as Lissajous ellipses. Emission spectroscopy and the analysis of the Hα/Hβ Stark broadening show the electron density along the Hβ line. Infrared thermography records a local temperature maximum in the jet–plasma interaction zone. The results provide a “passport” for the modes and confirm the existence of an energy-efficient pressure range of 20‒40 kPa for plasma-liquid applications.