Effective ionization coefficient in mixtures of Ar and O2 determined using the Townsend discharge

Abstract

Precise knowledge of the fundamental ionization properties of gases, such as the effective ionization coefficient, is crucial for discharges in mixtures of Ar:O2, which are significant for a wide range of plasma applications. This study determined the effective ionization coefficient in electronegative gas mixtures of Ar:O2 in the pressure range of 10–800 Torr and reduced electric field strength E/ N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. The reduced effective ionization coefficient α e/ N increased with E/ N and decreased with increasing O2 content in the gas mixture. The experimental results were compared with a model which was based on calculating the ionization and attachment coefficients with BOLSIG+. The ion conversion of O− to O2−, detachment from O2−, and formation of O3 were accounted for similarly as has been done with N2:O2 mixtures. Reasonably good agreement between the measurements and the model calculations was achieved for Ar:O2 mixtures with the O2 content between 20% and 70%. A discrepancy of more than 20% between measurement and calculations was observed at low E/ N values when the O2 content was below 20% and at high E/ N values when the O2 content was above 70%. Several possible explanations were proposed for the observed discrepancy; however, more elaborate models are required. The reduced critical electric field E/ N crit, where the apparent effective ionization coefficient is zero, was determined as a function of the O2 content in the Ar:O2 mixtures. E/ N crit increased with increasing O2 content in the mixture.

Determination of the apparent effective ionization coefficient in mixtures of He and O2 using steady-state Townsend discharge: effect of penning ionization and attachment

“…In our study with Ar:O 2 mixtures [51], the a model similar to that developed for N 2 :O 2 mixtures achieved a better agreement with measurements than standard BOLSIG + calculations of effective ionization coefficient (αη) [51]. It is thus expected that the net ionization in mixtures of He:O 2 is influenced by the processes considered in [51] with the addition of Penning ionization. Thus, the experimental determination of α ea /N in He:O 2 mixtures would complement the knowledge of processes affecting α ea /N which is an important input parameter required in theoretical models of APPs.…”

“…In pure O 2 or gas mixtures containing O 2 , attachment, detachment, O 3 − formation and charge transfer reactions are known to influence α e [50] and thus steady-state Townsend discharge experiments yields the apparent effective ionization coefficient α ea /N. In our study with Ar:O 2 mixtures [51], the a model similar to that developed for N 2 :O 2 mixtures achieved a better agreement with measurements than standard BOLSIG + calculations of effective ionization coefficient (αη) [51]. It is thus expected that the net ionization in mixtures of He:O 2 is influenced by the processes considered in [51] with the addition of Penning ionization.…”

“…The effective ionization coefficient was determined using the steady-state non-self-sustaining Townsend discharge. Only the important details are described here because the dark Townsend discharge set-up has been extensively described in previous studies by our group [46,49,51,52]. The reduced electric field strength E/N between the electrodes could be accurately set and varied by changing the voltage V applied to the cathode and varying the distance d between the electrodes.…”

The production of reactive chlorine species (RCS) by argon and helium plasma jets and the sensitivity of liver cancer cell HepG2 to RCS and H2O2 treatment

“…However, the concentration of metastable atoms is also influenced by the electron concentration and energy, which depend on the O 2 content in the plasma gas. [ 41,42 ]…”

“…However, the concentration of metastable atoms is also influenced by the electron concentration and energy, which depend on the O 2 content in the plasma gas. [41,42] 3.2 | RCS production efficiency by Ar/O 2 and He/O 2 plasma jets RCS production presumes plasma treatment of the saline in the noncontact mode. The noncontact mode was more difficult to achieve in the case of the Ar/O 2 plasma jet.…”