https://pubmed.ncbi.nlm.nih.gov/29146825/

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Abstract
Saint Elmo's fire and lightning are two known forms of naturally occurring atmospheric pressure plasmas. As a technology, nonthermal plasmas are induced from artificially created electromagnetic or electrostatic fields. Here we report the observation of arguably a unique case of a naturally formed such plasma, created in air at room temperature without external electromagnetic action, by impinging a high-speed microjet of deionized water on a dielectric solid surface. We demonstrate that tribo-electrification from extreme and focused hydrodynamic shear is the driving mechanism for the generation of energetic free electrons. Air ionization results in a plasma that, unlike the general family, is topologically well defined in the form of a coherent toroidal structure. Possibly confined through its self-induced electromagnetic field, this plasmoid is shown to emit strong luminescence and discrete-frequency radio waves. Our experimental study suggests the discovery of a unique platform to support experimentation in low-temperature plasma science.
Keywords:
hydrodynamic shear; luminescence; toroidal plasmoid; tribo-electricity; water jet.
Copyright © 2017 the Author(s). Published by PNAS.
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Conflict of interest statement
The authors declare no conflict of interest.
Figures
Fig. 1.
Close-up views in the flow…
Fig. 1.
Close-up views in the flow field of the impinging jet in air. (…
Fig. 1.
Close-up views in the flow field of the impinging jet in air. (
A) Photograph of the laminar jet in open air impinging on a polished quartz surface; the jet diameter is . The transition of the impinging round jet to an expanding radial jet can be seen through the sharp jet annulus. 85 μ m Inset schematic shows the jet in the context of the experimental setup with the nozzle and the wafer support plate. ( B) Optical access beneath the experimental setup was used to examine the visual …