Tuning the afterglow plasma composition in Ar/N₂/O₂mixtures: characteristics of a flowing surface-wave microwave discharge system

Abstract

A self-consistent kinetic model is used to study the possibility of tuning the plasma composition in the afterglow of a flowing surface-wave microwave discharge by the different discharge and system parameters in the case of 90%Ar-10%(N 2 -O 2 ) and N 2 -O 2 mixtures. The afterglow system consists of a 0.5 cm diameter quartz tube of 50 cm in length-where the discharge is generated and the early-afterglow develops-and an afterglow reactor. The plasma composition is studied at the end of the discharge plasma column and at the reactor inlet as a function of the N 2 :O 2 ratio for selected conditions, which are set with the system parameters and are illustrated in the experimental set-up. The validity of the model used is proven by the agreement of the calculated atomic densities with those measured by mass spectrometry.Due to the pressure drop along the tube, the position of the discharge (which also defines the lengths of the early-afterglow, t aft ) and the discharge pressure (p dis ) can be set with the position of the wave coupler-surfatron-along the tube at a constant gas flow rate (which defines the pressure in the reactor, p reac ). It is shown that the relative densities of species at the end of plasma column, which constitute the initial condition for the afterglow, depend on the discharge pressure. Therefore, at a constant gas flow rate with the position of the surfatron the plasma composition in the reactor is changing due to the variation of both the p dis and t aft . The evolution of the plasma composition is also studied when both the surfatron's position and the gas flow rate are changed, realizing conditions (i) with the same p dis , and different t aft and p reac , and (ii) with the same t aft , and different p dis and p reac .Comparing the N 2 -O 2 binary and the ternary mixtures, it is shown that the atomic densities obtained in the binary mixtures can be reproduced in ternary mixtures with different N 2 :O 2 ratios. Furthermore, according to the spectra measured in the afterglow reactor, comparable UV radiation can be achieved in both ternary and binary mixtures with the same O 2 content.

Characteristics of the flowing afterglow of a surface‐wave microwave discharge in a reactor loaded with a small diameter tube

“…The validity of the modeling scheme used was presented in several previous publications . In the discharge region, a very good agreement was found between the calculated and measured O and O 2 (a) densities determined at different N 2 percentages in the N 2 O 2 mixture and in pure O 2 in the case of a discharge generated with 2450 MHz in a 16 mm diameter tube at 1 Torr.…”

“…The pressure in the system, as discussed later in section 4.3.1. will vary based on the loading of the reactor. At these conditions, as indicated also by the emission spectra presented in section 9, in the reactor a neutral late‐afterglow plasma will be present …”

“…For treatment of heat sensitive polymers low temperature environment is required, which can be easily achieved in afterglow plasmas. The afterglow of a low pressure flowing surface‐wave microwave discharge has been found a proper medium, since it can be easily tuned to achieve high density of active species at low gas temperature . Although this system has been tested for several applications, the efficient treatment of objects with complex geometry is still an open question.…”

Characterization of a microwave plasma jet (TIAGO) in‐contact with water: Application in degradation of methylene blue dye

“…Images of the MWPJ at varying conditions of gas composition (5%, 15%, and 20% N 2 in Ar) and nozzle–water distance ( d = 5, 11, 22, and 44 mm) are depicted in Figure . The results show drastic changes in the visible emission of the MWPJ upon the addition of N 2 ; this is related to the change in the gas‐phase composition . Violet color can be observed close to the nozzle exit at 5% N 2 .…”

“…The results show drastic changes in the visible emission of the MWPJ upon the addition of N 2 ; this is related to the change in the gas-phase composition. [29,30] Violet color can be observed close to the nozzle exit at 5% N 2 . The plasma color becomes pink at higher N 2 percentages (15% and 20%).…”