Characterization of an atmospheric pressure plasma jet producing the auroral transition O(¹S) to O(¹D)

Abstract

We present a detailed characterization of an atmospheric pressure plasma jet that produces the metastable oxygen states O(1S) and O(1D) with emission of the “auroral” green line. The device used 99.999% pure argon as a working gas for the plasma generation. Optical emission spectroscopy was used to understand the active species present in the plasma jet and to infer the mechanism of O(1S) creation and destruction. The continuum spectrum was used in conjunction with a method based on machine learning for determining the arbitrary electron probability distribution function. Discharge and plasma properties were estimated from Lissajous plots and using calculations with the BOLSIG+ software. The metastable oxygen forms for all operating parameters of the plasma jet system in a linear electrode configuration. The camera images provided information of the overall plasma jet behavior as parameters were altered. While the metastable oxygen was produced for every iteration, the plasma jet behavior changed considerably when the powered and grounded electrodes are switched. Small admixtures of oxygen and nitrogen were introduced in the plasma jet to understand the kinetic processes of metastable oxygen destruction and the 557.7 nm auroral line. This behavior has implications for plasma reactive chemistry in fundamental areas such as auroral physics as well as technological applications of plasmas.

Characteristics of the O(1S) to O(1D) 557.7 nm green emission observed in an argon plasma jet

“…In atmospheric pressure N 2 discharge, the lifetime of O( 1 S) was estimated to be in the range of 1-20 ms by comparing the intensity ratio of 557.7 nm to the competing line at 297.2 nm with the theoretical ratio [37]. Given the existence of ArO(1S) excimer, if taking the increased transition probability by a factor of 576 calculated in [19] into account, the lifetime of ArO( 1 S) is also on the order of 1-2 ms, which is several tens of times the discharge period in our experiment.…”

“…The rise in T e in this regime would be likely to cause an increase in the density of Ar atoms in the metastable levels, which can be proved in figure 9(a), as those are typically populated by direct electron impact. Ar metastables (their energy levels are at 11.5-11.8 eV) are expected to increase atomic oxygen density providing that the dissociative excitation of O 2 is principally driven by the reaction [ The dissociation of O 2 is most probably driven by electron impact, as also indicated in [19]. The weak intensity of the 777.4 nm line from the spectrum (figure 2), indicates that the downstream region of this discharge operates at electron energies that are lower than typically observed in DBDs.…”

“…Electrons and Ar metastable states are the two most important active species in this gas system, where they can play different roles in the dissociation of molecules and excitation of atoms, affecting the plasma properties. Jaiswal et al did some work on the electron density and electron temperature obtained from the green afterglow, concluding that electron impact is a more probable way for generating O( 3 P) and stepwise exciting it to O( 1 S), while the crucial function of Ar atoms is to form the excimer ArO( 1 S) [19]. Nevertheless, the electron behavior was not given much consideration, for instance, the relationship between the electron properties and the variation of green emission intensity has not been fully discussed.…”

“…In [14,15,17,19], a two-ring double DBD jet structure was used and the afterglow always looked diffuse without obvious change of discharge morphology. Judée et al reported that the plasma characteristics are 7%-16% higher in the single DBD configuration compared to the double DBD configuration for the same plasma power [20].…”

Partial EEDF analysis and electron diagnostics of atmospheric-pressure argon and argon–helium DBD plasma

“…Through this, the impact of inconsistencies in the OES setup, discharge conditions or optical calibration can be reduced. The basic principles and limitations of this method were discussed in [45][46][47]. This paper shows the measured spectra and EEDF results of OES measurements from a CAPP DBD.…”