Spatially-periodic microplasmas in complex microchannel networks: Wall-plasma interactions and dynamic behavior

J. H. Cho, H. J. Yang, S. J. Park, J. G. Eden

Research output: Contribution to journalArticle

Abstract

Wall-plasma interactions have been observed for spatially-periodic microplasmas generated in 300-700 μm wide channels fabricated in nanoporous alumina. Examination of Ne microplasma discs produced in a standing-wave pattern in Al2O3 channels illustrates the competition between electron production at the sheath-wall interface and loss by recombination in an atmospheric pressure background. Two topologies of the microplasma arrays are observed. For channel widths (d) less than 450 μm, the microplasmas are generally centered in the channel and sustained by electron generation at both plasma sheath/channel wall interfaces, presumably including the release of charge residing in the hexagonal alumina pores. As d is progressively increased from 300 to 450 μm, the microchannel plasma cross-section is gradually transformed from circular to elliptical, and its surface area declines by as much as 50% so as to minimize e - losses to the background gas. Increasing d above ∼450 μm abruptly switches the topology to one in which plasmas having a triangular cross-section attach to one of the channel walls in a pattern that alternates along the channel axis. Microfabricating trapezoidal cross-section channels into complex geometries, including the Cornu spiral and intersecting linear arrays, also reveals dynamic behavior in the propagation of microplasmas. For a common spiral structure, observations of plasma expansion show the wavefront propagates over the corrugated surface or within the channel with radial and azimuthal velocities of 3 ±1 km s-1 and 8 ± 1.5 km s-1, respectively. Plasma formation is initiated in each ring of the spiral through electron seeding by streamers propagating radially outward at velocities approaching 200 km s-1. In addition to electrostatic charge-mediated variations in the mean separation between adjacent microplasmas, the time-dependent interference between two 1D microplasma arrays has been observed during plasma expansion. Reproducible ignition of a microplasma ensemble along ridges micromachined into channels near the intersections of two linear arrays has also been realized. The results reported here demonstrate that microchannels with the walls overcoated with any of a variety of materials provide a promising platform for examining in detail the interaction of low temperature plasma with a surface of arbitrary composition and topography.

Original languageEnglish (US)
Article number375202
JournalJournal of Physics D: Applied Physics
Volume52
Issue number37
DOIs
StatePublished - Jul 16 2019

Keywords

  • microplasma
  • plasma packets
  • wall-plasma interaction

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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