Experimental and PIC MCC study of electron cooling—re-heating and plasma density decay in low pressure rf ccp argon afterglow

Abstract

In this work, experimental and theoretical study of pulsed discharge in argon has been carried out. The experimental data on the dynamics of electron density, electron temperature, and plasma potential have been obtained by probe measurements (using hairpin and Langmuir probes) in the afterglow between two RF pulses. This dynamics is thoroughly analyzed by comparison with the results of the kinetic PIC MC simulations. The main processes that cause electron cooling have been revealed for two different time stages. The first afterglow stage is characterized by the rapid decrease of the electron temperature. During this stage, inelastic electron collisions with Ar atoms in the ground state play an important role in the electron cooling. During the second long-scale stage, only diffusion along the electron energy scale via Coulomb or elastic collisions can provide the observed effect of the gradual electron cooling. The effects of elastic and Coulomb collisions on the electron cooling have been separated and analyzed by means of PIC MC simulations. The temporal evolution of the electron concentration spatial distribution and the plasma boundary sheaths size has been also analyzed on the base of 1D PIC MC simulations. A good agreement between the probe measurements and the PIC simulations data on plasma density, ambipolar potential and electron temperature is observed. To perform a more detailed study of EEDF and electron temperature dynamics, the relative intensity of Ar(2p1) → Ar(1s2) emission at 750 nm has been measured. A very good agreement between the measured emission intensity and the calculated excitation rate of Ar(2p1) at different time scales validates the electron temperature temporal dynamics obtained by the used PIC model.