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Enhanced plasma production by ambipolar electric fields in convergent magnetic fields

Kazunori Takahashi1,*, Christine Charles2, Rod W. Boswell2, and Antonella Caldarelli3

  • 1Department of Electrical Engineering, Tohoku University, Sendai 980-8579, Japan
  • 2Space Plasma, Power and Propulsion Laboratory, Research School of Physics, The Australian National University, Canberra ACT 2601, Australia
  • 3Institut de Combustion, Aérothermique, Réactivité et Environnement, CNRS, 45071 Orléans, France

  • *Contact author: kazunori.takahashi.e8@tohoku.ac.jp
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Phys. Rev. Research 8, 023322 – Published 22 June, 2026

DOI: https://doi.org/10.1103/86rf-6dvz

Abstract

Controlled unidirectional remote plasma production in a radio-frequency (rf) plasma source is demonstrated by placing magnetic nozzle throat several tens of centimeters away from the rf antenna, where a local density peak forms near the throat. The experiment indicates that the dominant electron energization mechanism responsible for the density peak in the magnetic nozzle throat is electrostatic electron acceleration driven by a spontaneously formed ambipolar electric field, yielding an energy gain of approximately 5 eV and enhanced remote ionization. These results establish plasma sources driven by spontaneous electrostatic electron acceleration.

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Phys. Rev. Research 8, 023322– Published 22 June, 2026
  • Received 21 January 2026
  • Revised 14 April 2026
  • Accepted 3 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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