• TrendMD is the leading scholarly content discovery solution.
  • Sign-up for PNAS eTOC Alerts

Toroidal plasmoid generation via extreme hydrodynamic shear

  1. Francisco J. Alves Pereirac,d,1
  1. aGraduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125;
  2. bSchool of Mechanical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel;
  3. cIstituto Nazionale per Studi ed Esperienze di Architettura Navale, Consiglio Nazionale delle Ricerche (CNR-INSEAN), Rome 00128, Italy;
  4. dGraduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125
  1. Edited by Parviz Moin, Stanford University, Stanford, CA, and approved October 16, 2017 (received for review July 20, 2017)


Plasmas at atmospheric pressure conditions are ubiquitous, in natural form, such as the familiar lightning, or produced through artificially created electromagnetic or electrostatic fields for industrial and scientific applications. One distinctive feature of these cold-type plasmas is their lack of a topologically defined shape, concurrent with spatial unsteadiness and nonuniformity. Here, we report the observation of a coherent and stable toroidal plasma that spontaneously forms under extreme hydrodynamic shear, without external electromagnetic action. The confined and chamberless nature of this plasmoid has potential implications for the investigation of plasma–matter interactions, in the development of plasma-based deposition techniques for the microelectronics industry, in the emerging field of plasma medicine, or as a model for energy-storing self-maintained plasmoids.


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.


  • ?1To whom correspondence may be addressed. Email: francisco.alvespereira{at}cnr.it or mgharib{at}caltech.edu.
  • 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.danielhellerman.com/lookup/suppl/doi:10.1073/pnas.1712717114/-/DCSupplemental.

Online Impact

  • 864971864 2018-01-22
  • 258841863 2018-01-22
  • 957295862 2018-01-22
  • 553518861 2018-01-22
  • 983792860 2018-01-22
  • 539694859 2018-01-22
  • 956115858 2018-01-22
  • 730379857 2018-01-22
  • 346624856 2018-01-22
  • 201609855 2018-01-22
  • 72549854 2018-01-21
  • 795928853 2018-01-21
  • 752345852 2018-01-21
  • 566508851 2018-01-21
  • 615722850 2018-01-21
  • 689612849 2018-01-21
  • 846903848 2018-01-21
  • 674896847 2018-01-21
  • 11197846 2018-01-21
  • 986896845 2018-01-21