Apparent secondary-electron emission coefficient and the voltage-current characteristics of argon glow discharges

The accuracy of secondary-electron emission coefficients, that are used as input data of discharge models, seriously influences the calculated discharge characteristics. As it is very difficult to consider all possible electron emission processes of a cold cathode separately, in most of the recent models an apparent secondary coefficient gamma is applied, which is often assumed to be constant, even for a wide range of discharge conditions. In contrast with this common assumption, the present calculations-based on a heavy-particle hybrid model-show that in abnormal glow discharges gamma varies considerably with changing discharge conditions: a factor of 3 change of gamma has been found in the range of reduced current densities (0.04 mA cm(-2) Torr(-2)< or =j/p(2)< or =4 mA cm(-2) Torr(-2)) covered in this study. The present simulations also confirm that ionization by heavy particles plays a significant role in the ion production at the abnormal cathode fall. Moreover, it is shown, that the fast heavy particles reflected from the cathode surface play the dominant role in the gas heating.