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Abstract
Creation of the “auroral” green line, a fascinating occurrence commonly observed in the upper atmosphere, has long been a difficult endeavor, especially at atmospheric pressure. Here we report strong emission of the “auroral” green line for the first time in a kHz frequency, linear field atmospheric pressure plasma jet system. The device used 99.999% pure argon as a working gas for the plasma generation. Optical emission spectroscopy measurements of the after discharge region show the existence of 557.7 nm emission which corresponds to the transition O(^1S)–O(^1D). The intensity of the produced green line is strong enough that the entire plasma plume in the ambient air is visible as a green plasma. We provide the chemical reactions of O(^1S) production in the plasma and the estimation of the density of the O(^1S) metastable state using the kinetic reactions. Further, the O(^1S) emission is characterized by changing the flow rate of argon, applied voltage and electrode gap. The adequate plasma length (> 25 , hbox {mm}) along with the production of a variety of reactive components viz; OH, {hbox {N}}_{2}^{+} and oxygen (777 nm) make this configuration useful for applications such as: blood coagulation, cancer treatment, sterilization, and waste treatment. Moreover, this setup can be potentially used as a test bed for the in-depth understanding of plasma chemistry relevant to the aurora and comet tails using a laboratory setting.
Highlights
Creation of the “auroral” green line, a fascinating occurrence commonly observed in the upper atmosphere, has long been a difficult endeavor, especially at atmospheric pressure
Given the abundance of O2 in ambient air and the process of atmospheric pressure plasma jets (APPJs), atomic oxygen produces the emission of the green “auroral” line; a brilliant green line of wavelength 557.7 nm
We present the first investigation on the novel phenomenon of auroral green line emission in an APPJ using a kHz frequency plasma source
Summary
Creation of the “auroral” green line, a fascinating occurrence commonly observed in the upper atmosphere, has long been a difficult endeavor, especially at atmospheric pressure. Given the abundance of O2 in ambient air and the process of APPJs, atomic oxygen produces the emission of the green “auroral” line; a brilliant green line of wavelength 557.7 nm. The source of this line is the transition between metastable states of oxygen O(1S) → O(1D). At higher pressure (> 10 Torr), an O2 deficient environment is required to sustain the O(1 S) line[6] This is the reason why the green line is typically observed in altitudes (> 100 km ) where lighter atoms (such as O) are more abundant than the heavy oxygen molecule. An open atmosphere often makes it difficult to observe such lines due to high collision rates and strong abundance of quenching molecules such as O2 and N2
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