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Title: High ionisation fraction plasmas in a low temperature, multidipole cusp plasma

Abstract

The depletion of neutral helium atoms has been studied in an unmagnetised spherical plasma created by DC discharge in a multidipole confinement field. Knowing the neutral density profile is critical to predicting the equilibrium flow of such plasmas. A model of the emissivity due to electron-impact excitation of neutral atoms in the plasma has been derived and used to fit radiance measurements of several neutral transitions to extract the radial profile of neutral density for plasmas of varying temperature and density. We report a depletion of the core neutral density varying between negligible levels to 80 % of the edge neutral density depending on the input power and fuelling. The corresponding ionisation fraction varies between 30–80 % in the plasma core. A simple neutral diffusion model is sufficient to describe the shape of neutral density profile implied by the radiance measurements. We have used the measurements to include a drag force due to neutral charge-exchange collisions in simulations of driven plasma flow. The simulation predicts a better fit to Mach probe flow measurements when this neutral drag is accounted for. This study shows that accounting for a realistic neutral profile is important to predict the plasma flow geometry and its magnetohydrodynamics (MHD)more » stability.« less

Authors:
 [1];  [2];  [2];  [2];  [2]; ORCiD logo [2]
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  1. Univ. of Lyon, CNRS (France). Physics Lab.
  2. Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); National Science Foundation (NSF); Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, TN (United States); National Center for Scientific Research (CNRS). International Project for Scientific Cooperation (PICS); French National Research Agency (ANR)
OSTI Identifier:
1464937
Grant/Contract Number:  
SC0008709; PHY 0923258; PHY 0821899; ANR-13-JS04-0003-01
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 84; Journal Issue: 03; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma diagnostics; plasma dynamics; plasma flows

Citation Formats

Désangles, V., Milhone, J., Cooper, C., Weisberg, D. B., Nornberg, M. D., and Forest, C. B. High ionisation fraction plasmas in a low temperature, multidipole cusp plasma. United States: N. p., 2018. Web. doi:10.1017/S0022377818000533.
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Désangles, V., Milhone, J., Cooper, C., Weisberg, D. B., Nornberg, M. D., & Forest, C. B. High ionisation fraction plasmas in a low temperature, multidipole cusp plasma. United States. doi:10.1017/S0022377818000533.
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Désangles, V., Milhone, J., Cooper, C., Weisberg, D. B., Nornberg, M. D., and Forest, C. B. Tue . "High ionisation fraction plasmas in a low temperature, multidipole cusp plasma". United States. doi:10.1017/S0022377818000533. https://www.osti.gov/servlets/purl/1464937.
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@article{osti_1464937,
title = {High ionisation fraction plasmas in a low temperature, multidipole cusp plasma},
author = {Désangles, V. and Milhone, J. and Cooper, C. and Weisberg, D. B. and Nornberg, M. D. and Forest, C. B.},
abstractNote = {The depletion of neutral helium atoms has been studied in an unmagnetised spherical plasma created by DC discharge in a multidipole confinement field. Knowing the neutral density profile is critical to predicting the equilibrium flow of such plasmas. A model of the emissivity due to electron-impact excitation of neutral atoms in the plasma has been derived and used to fit radiance measurements of several neutral transitions to extract the radial profile of neutral density for plasmas of varying temperature and density. We report a depletion of the core neutral density varying between negligible levels to 80 % of the edge neutral density depending on the input power and fuelling. The corresponding ionisation fraction varies between 30–80 % in the plasma core. A simple neutral diffusion model is sufficient to describe the shape of neutral density profile implied by the radiance measurements. We have used the measurements to include a drag force due to neutral charge-exchange collisions in simulations of driven plasma flow. The simulation predicts a better fit to Mach probe flow measurements when this neutral drag is accounted for. This study shows that accounting for a realistic neutral profile is important to predict the plasma flow geometry and its magnetohydrodynamics (MHD) stability.},
doi = {10.1017/S0022377818000533},
journal = {Journal of Plasma Physics},
number = 03,
volume = 84,
place = {United States},
year = {2018},
month = {6}
}
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DOI:  10.1017/S0022377818000533
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Figure 1 Figure 1: Schematic of the 1.50 m radius BRB vessel with the spectrometer radiance measurement geometry.
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