Direct measurement of the transition from edge to core power coupling in a light-ion helicon source

P. A. Piotrowicz, J. F. Caneses, M. A. Showers, D. L. Green, R. H. Goulding, J. B.O. Caughman, T. M. Biewer, J. Rapp, D. N. Ruzic

Research output: Contribution to journalArticlepeer-review

Abstract

We present time-resolved measurements of an edge-to-core power transition in a light-ion (deuterium) helicon discharge in the form of infra-red camera imaging of a thin stainless steel target plate on the Proto-Material Exposure eXperiment device. The time-resolved images measure the two-dimensional distribution of power deposition in the helicon discharge. The discharge displays a mode transition characterized by a significant increase in the on-axis electron density and core power coupling, suppression of edge power coupling, and the formation of a fast-wave radial eigenmode. Although the self-consistent mechanism that drives this transition is not yet understood, the edge-to-core power transition displays characteristics that are consistent with the discharge entering a slow-wave anti-resonant regime. RF magnetic field measurements made across the plasma column, together with the power deposition results, provide direct evidence to support the suppression of the slow-wave in favor of core plasma production by the fast-wave in a light-ion helicon source.

Original languageEnglish (US)
Article number052101
JournalPhysics of Plasmas
Volume25
Issue number5
DOIs
StatePublished - May 1 2018

ASJC Scopus subject areas

  • Condensed Matter Physics

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