Characteristics of an atmospheric microwave-induced plasma generated in ambient air by an argon discharge excited in an open-ended dielectric discharge tube

Abstract

Parametric observations on an atmospheric-pressure plasma sustained in ambient air by an argon discharge excited by 2.45 GHz microwaves in an open-ended dielectric discharge tube are reported. Microwave power, discharge tube dimensions, and argon flow rate were the major operating parameters. Three distinctive plasma regions were observed: plasma filaments exiting from the discharge tube, converging point of these filaments, and a plasma flame. At the filament-converging point, argon atom excitation temperature, rotational temperature, and electron density were measured by optical emission spectroscopy ͑OES͒ in the operating range of ͑3.0-5.0͒ liters per minute of gas flow rate and ͑650-950͒ W of microwave power. The measured excitation temperature and rotational temperature were ͑5000-5800͒ K and ͑2800-3400͒ K, respectively. The electron density obtained by Stark broadening width of the H ␤ line showed (5.0-8.0) ϫ10 14 cm Ϫ3 . It was observed that the volume of the plasma flame and the gas temperature were increased with increasing the microwave power. On the other hand, higher gas flow rates increased the electron density. In the plasma flame, the gas temperature measured by a thermocouple and OES was in the range of ͑1030-2200͒ K, which showed an exponential decrease in the axial direction away from the converging point.

Measuring the electron temperature by optical emission spectroscopy in two temperature plasmas at atmospheric pressure: A critical approach

“…According to the experimental results obtained by different authors, these conditions are often found in microwave discharges at atmospheric pressure. 2,3 Thus, García et al 3 obtained radially averaged measurements of the gas temperature, excitation temperature, and electron densities in an argon capillary surface-wave plasma at atmospheric pressure. Their axial results show electron densities in the range of 10 −20 m −3 , gas temperatures of 1300 K, and excitation temperatures ranging from 0.7 to 0.3 eV.…”

“…These results could explain the low values of electron temperatures reported in some works on argon microwave discharges at atmospheric pressure. 2,3 …”

“…The problem arises when the gas is sensibly cooler than the electrons, as it is the case of some microwave discharges at atmospheric pressure. 2,3 In these plasmas, the electron temperatures experimentally measured from the excitation temperature yield values that for the case of argon may be well below 0.4 eV, while the electron densities measured are over 10 20 m −3 . For these discharges, there are some experimental evidences that show that the excitation temperature can be higher than the electron temperature.…”

“…[1][2][3] As the interpretation of the data obtained with electric probes at such pressures is not clear, 4 many experimental works have focused on the use of optical emission spectroscopy ͑OES͒ as a way of characterizing the fundamental parameters of the discharge, either calculating the broadening of the emission lines to obtain the electron density, 5 modeling emission bands of some species to get the gas temperature, 6 or simply by recording the emission of the different excited states in order to get the electron temperature assuming a Bolztmann-like distribution of the population of the emitting excited levels. 3 The determination of the electron mean kinetic energy through this method is based on the identification of the excitation temperature obtained with the electron temperature.…”

Investigation of Synthesis‐Gas Production via CH4O2Ar Gas Mixture Using Microwave Plasma Torch

“…Moreover, typical MW plasma torch operated at 2.45 GHz produced maximum temperature of 6 000 K at atmospheric pressure while operated by 2 000 W power. [16] For Ar MW plasma at 1 atm with power range of 650-950 W, the thermocouple and optical emission spectroscopy showed temperature of 1 030-2 200 K. [17] In other literature for up to 600 W MW power, lower temperature plasma zone of 500-1 000 K at low pressure near the discharge volume have been estimated. [1] However, regarding our experimental set-up running with maximum MW power of 300 W, regarding ref.…”