Sheath Dynamics and Characteristics in Radio-Frequency Atmospheric Pressure Glow Discharges

Abstract

Summary form only given. Both experimental and computational studies have in the past established that the sheath region of radio-frequency atmospheric pressure glow discharges may be modeled, as the first approximation, by a capacitor. Experimentally the capacitance of the sheath region can be measured indirectly by measuring plasma reactance. In turn this can be used to deduce the sheath thickness. Since the sheath thickness is a function of electron temperature, electron density and sheath voltage, the measurement of the sheath thickness can potentially lead to routes to determine electron temperature, electron density or sheath voltage if one can establish their relationship. This contribution is an attempt to establish the generic dependence of sheath thickness on electron temperature, electron density and sheath voltage in radio-frequency atmospheric pressure glow discharges. Using a simulation tool that has been developed for radio-frequency atmospheric helium discharges; we studied sheath dynamics over a wide range of discharge currents from the low-current alpha mode to the high-current gamma mode. Sheath thickness is calculated and presented as a function of electron density, electron temperature and sheath voltage. To contrast out their generic correlations, we compared the numerically obtained dependence to the collisional sheath model of Child's law. Discussion is presented to establish (1) the possibility of a generic relationship and (2) the potential of using such relationship to develop new diagnostic methodologies