Electron cooling and plasma density decay in early afterglow of low pressure argon plasmas

Abstract

The spatio-temporal evolution of the electron density and the electron temperature in afterglow is investigated by both Langmuir probe measurement and a fluid model for capacitively coupled argon discharges with a pressure range of 5 ~ 90 mTorr. It is found that, depending on the discharge condition, the plasma density profile and its evolution can have a significant influence on the plasma density decay rate in the afterglow. As a result, the rate of electron cooling will also be affected through the diffusive cooling mechanism. In addition, at a given gas pressure, the electron cooling rate significantly decreases with decreasing plasma density, due to the diminishing e–e scattering process for the generation of energetic electrons which can escape to the wall. The measured temporal evolution of both the plasma density and the electron temperature in the afterglow at different pressures is compared with the modeling results obtained in this work as well as those from other models reported in the literature.