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

doi:10.1063/1.5023924

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

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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 language	English
Article number	052101
Journal	Physics of Plasmas
Volume	25
Issue number	5
DOIs	https://doi.org/10.1063/1.5023924
State	Published - May 1 2018

Funding

This material is based on the work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Contract No. DEAC05-00OR22725. This manuscript was authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http:// energy.gov/downloads/doe-public-access-plan).

Funders	Funder number
U.S. Department of Energy
Fusion Energy Sciences	DEAC05-00OR22725
Office of Science
U.S. Department of Energy

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

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.",

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

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doi = "10.1063/1.5023924",

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AU - Piotrowicz, P. A.

AU - Caneses, J. F.

AU - Showers, M. A.

AU - Green, D. L.

AU - Goulding, R. H.

AU - Caughman, J. B.O.

AU - Biewer, T. M.

AU - Rapp, J.

AU - Ruzic, D. N.

PY - 2018/5/1

Y1 - 2018/5/1

N2 - 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.

AB - 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.

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

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