Three modes in a radio frequency atmospheric pressure glow discharge

TLDR

Atmospheric pressure glow discharges operate without a vacuum chamber, offering promising material‑processing applications. The study aims to characterize the operation range of a radio‑frequency APGD and investigate transitions between its glow modes. The authors performed experimental measurements of discharge voltage, current, plasma power, and impedance, and examined sheath‑breakdown‑driven transitions between glow modes. Three spatially uniform glow modes—normal, abnormal, and recovery—were identified, revealing a broader operational range, with sheath breakdown driving mode transitions and impedance matching critically affecting plasma stability.

Abstract

Fundamentally not requiring a vacuum chamber, atmospheric pressure glow discharges (APGDs) offer an exciting prospect for a wide range of material processing applications. To characterize their operation and establish their operation range, a radio frequency (rf) APGD is studied experimentally with measurement of discharge voltage, current, dissipated plasma power and plasma impedance. Different from the current understanding that rf APGD are operative only in the abnormal glow mode, we show the presence of two additional modes namely the normal glow mode and the recovery mode. It is shown that all three modes are spatially uniform and possess key characteristics of a glow discharge. So rf APGD have a much wider operation range than previously believed. To provide further insights, we investigate the transition from the abnormal glow mode to the recovery mode. It is established that the cause responsible for the mode transition is sheath breakdown, a phenomenon that is known in low- and moderate-pressure glow discharges but has not been reported before for atmospheric-pressure glow discharges. Finally we demonstrate that plasma dynamics, hence plasma stability, in these three modes are influenced crucially by the impedance matching between the plasma rig and the power source.