Toroidal plasmoid generation via extreme hydrodynamic shear
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.
© 2017 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). Edited by Parviz Moin, Stanford University, Stanford, CA, and approved October 16, 2017 (received for review July 20, 2017). We thank B. Abiri, J. Adams, Prof. A. Hajimiri, S. Hufstedler, D. Jeon, J. Meier, K. Mendoza, D. Rinderknecht, and K. Sharafi, who in various stages of this project helped by participating in experiments or provided expertise for the diagnostics or experimental setup. We also thank Prof. P. M. Bellan for kindly reviewing the plasma analysis and for bringing the ion acoustic wave instability to our attention. The work was supported by California Institute of Technology internal funds and the Charyk Foundation. We dedicate the work to our late teacher and colleague Prof. Anatol Roshko. Author contributions: M.G. and F.J.A.P. designed research; M.G., S.M., M.R., M.B., and F.J.A.P. performed research; M.G., S.M., M.B., and F.J.A.P. analyzed data; M.G. and F.J.A.P. wrote the paper; M.R. contributed the numerical simulation; and F.J.A.P. performed the spectroscopic, plasma, and physico-chemical analyses. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1712717114/-/DCSupplemental.
Published - PNAS-2017-Gharib-12657-62.pdf
Supplemental Material - pnas.1712717114.sm01.mp4
Supplemental Material - pnas.1712717114.sm02.mp4