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\mathrm {appls} ), the critical V\mathrm {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. [ABSTRACT FROM AUTHOR]