Alpha to Gamma Mode Transitions in Pulse-Modulated Radio Frequency Atmospheric Pressure Glow Discharges

In pulse-modulated (PM) radio frequency (RF) atmospheric pressure glow discharges (APGDs), the alpha-gamma mode transition is analyzed and confirmed with I-V characteristic curve. The behaviors of alpha-gamma mode transition in PM RF APGDs are more complicated than that in continuous wave (CW) RF APGDs. In terms of amplitude of applied RF voltage just before a pulse falling edge (V
_appls
), the critical V
_appls
at the alpha-gamma mode transition in a PM RF APGD increases with the decreasing duty ratio and is higher than that of a CW RF APGD. The feature of the alpha-gamma mode transition in a PM RF APGD is attributed to the gas temperature rise depending on both the RF voltage and duty ratio. The alpha-gamma mode transition is verified to occur at the initial phase of a PM RF APGD and the onset is earlier at a higher transient RF voltage. As the mode transition occurs, a RF voltage spike is formed in the pulse waveform.