Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas
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ReinkeParallelPoP13.pdf
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Author(s)
Reinke, Matthew Logan
Rice, John E.
Greenwald, Martin J.
Howard, Nathaniel Thomas
Hutchinson, Ian Horner
Hubbard, Amanda E
Hughes Jr, Jerry
Terry, James L
Wolfe, Stephen M
Date Issued
May 2013
Journal
Physics of Plasmas
Publisher
American Institute of Physics (AIP)
Citation
Reinke, M. L., I. H. Hutchinson, J. E. Rice, M. Greenwald, N. T. Howard, A. Hubbard, J. W. Hughes, J. L. Terry, and S. M. Wolfe. “Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas.” Physics of Plasmas 20, no. 5 (2013): 056109. © 2013 AIP Publishing LLC
Version
Final published version
Abstract
Measurements of poloidal variation, [˜ over n][subscript z]/⟨n[subscript z]⟩ , in high-Z impurity density have been made using photodiode arrays sensitive to vacuum ultraviolet and soft x-ray emission in Alcator C-Mod plasmas. In/out asymmetries in the range of −0.2 < n[subscript z,cos]/⟨n[subscript z]⟩ < 0.3 are observed for r/a < 0.8 , and accumulation on both the high-field side, n[subscript z,cos] < 0, and low-field side, n[subscript z,cos] > 0, of a flux surface is found to be well described by a combination of centrifugal, poloidal electric field, and ion-impurity friction effects. Up/down asymmetries, −0.05 < n[subscript z,sin]/⟨n[subscript z]⟩ < 0.10, are observed over 0.5 < r/a < 0.9 with n[subscript z,sin] > 0 corresponding to accumulation opposite the ion ∇ B drift direction. Measurements of the up/down asymmetry of molybdenum are found to disagree with predictions from recent neoclassical theory in the trace limit, n[subscript z]Z[superscript 2]/n[subscript i] ≪ 1. Non-trace levels of impurities are expected to modify the main-ion poloidal flow and thus change friction-driven impurity density asymmetries and impurity poloidal rotation, v[subscript θ,z] . Artificially modifying main-ion flow in parallel transport simulations is shown to impact both [˜ over n][subscript z]/⟨n[subscript z]⟩ and v[subscript θ,z], but simultaneous agreement between measured and predicted up/down and in/out asymmetry as well as impurity poloidal rotation is not possible for these C-Mod data. This link between poloidal flow and poloidal impurity density variation outlines a more stringent test for parallel neoclassical transport theory than has previously been performed. Measurement and computational techniques specific to the study of poloidal impurity asymmetry physics are discussed as well.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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DOI of Published Version
https://doi.org/10.1063/1.4802197
