alpha, gamma, and normal, abnormal glow discharge modes in radio-frequency capacitively coupled discharges at atmospheric pressure

Abstract

Discharge modes, alpha and gamma, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5 mm. As similarly observed in other experiments, the alpha and gamma mode and the alpha-gamma mode transition were observed with large drops in the voltage (310-179 V) and the phase angle between the voltage and current (54 degrees-18 degrees), and a contraction of the plasma volume (8.5-0.17 cm(3), at 3 mm gap distance). The discharge voltage where the alpha-gamma mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the alpha mode. At 1 and 2 mm, the alpha mode remained in the abnormal glow discharge until the alpha-gamma mode transition occurred as the discharge current increases. At 3 mm, however, the alpha mode was excited as a normal glow discharge with a constant current density (17 mA/cm(2)) but it became an abnormal glow discharge as the current increased. At 4 mm, the alpha mode was sustained as a normal glow discharge, then the transition to the gamma mode occurred. Using a simple resistor-capacitor circuit model and a alpha sheath breakdown model, the discharge modes and the mode transition properties were studied. (c) 2006 American Institute of Physics.