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  • Open Access

Helicon plasma mode transitions at low magnetic fields

Landon D. Bevier* and Justin M. Little

  • *Contact author: ldbevier@gmail.com
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Phys. Rev. Research 8, 023177 – Published 18 May, 2026

DOI: https://doi.org/10.1103/13gy-rz2v

Abstract

The nature of a low-field helicon plasma mode transition is examined using experiment and theory. Tests in a radio frequency plasma source reveal an abrupt transition between helicon and capacitive discharge modes that occurs at a critical magnetic field strength. To characterize the mode transition, a global model for low-field m=0 helicon plasmas is developed based on power absorption via Landau damping. A general scaling law for the critical field strength is derived from the model and experimentally validated using measurements of electron density and temperature. The assumption of power absorption via Landau damping in the model leads to a critical condition for the ratio of wave phase velocity and electron thermal velocity. Measurements of wave phase velocity and electron temperature while operating on mixtures of argon and N2O support the theoretical prediction and show that the mode transition depends on electron properties rather than on the ion and neutral composition. Agreement between theory and experiment shows that Landau damping is the primary power absorption mechanism in low-field, conducting boundary helicon plasmas.

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Phys. Rev. Research 8, 023177– Published 18 May, 2026
  • Received 8 December 2025
  • Accepted 29 April 2026
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