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Title: Up/Down Impurity Density Asymmetries in C-Mod Plasmas

Abstract

Brightness profiles of x-ray emission from H-like Ar17+ exhibit a distinct up/down asymmetry under certain operating conditions in C-Mod plasmas, indicating that impurity densities are not constant on flux surfaces with r/a between ~0.8 and ~0.95. In L- and I-mode plasmas, there is an x-ray brightness excess, up to a factor of 8, on the side opposite to the ion BxgradB drift direction. This effect is not observed in H-mode plasmas, presumably due to edge impurity transport being dominated by a strong inward pinch, which is absent in L- and I-mode. The magnitude of the asymmetry in L- and I-mode decreases with increasing plasma current, similar to the observed decrease in radial impurity diffusivity. In I-mode, where the codependence between electron density and temperature can be broken with ICRF heating power, the asymmetry magnitude is found to decrease with increasing density and with increasing edge temperature at fixed density. These measurements exhibit some qualitative features of neo-classical expectations but the observed asymmetry magnitude is much larger than predicted and some scalings with plasma parameters are not seen. The up/down asymmetry appears to be largest when the cross field impurity diffusivity is the highest.

Authors:
; ; ; ; ; ; ;
Publication Date:
DOE Contract Number:  
FC02-99ER54512
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1881422
DOI:
https://doi.org/10.7910/DVN/XCNLJZ

Citation Formats

Rice, J. E., Reinke, M. L., Cao, N., Hughes, J. W., Ashbourn, J. M. A., Ernst, D. R., Hubbard, A. E., and Irby, J. H. Up/Down Impurity Density Asymmetries in C-Mod Plasmas. United States: N. p., 2019. Web. doi:10.7910/DVN/XCNLJZ.
Rice, J. E., Reinke, M. L., Cao, N., Hughes, J. W., Ashbourn, J. M. A., Ernst, D. R., Hubbard, A. E., & Irby, J. H. Up/Down Impurity Density Asymmetries in C-Mod Plasmas. United States. doi:https://doi.org/10.7910/DVN/XCNLJZ
Rice, J. E., Reinke, M. L., Cao, N., Hughes, J. W., Ashbourn, J. M. A., Ernst, D. R., Hubbard, A. E., and Irby, J. H. 2019. "Up/Down Impurity Density Asymmetries in C-Mod Plasmas". United States. doi:https://doi.org/10.7910/DVN/XCNLJZ. https://www.osti.gov/servlets/purl/1881422. Pub date:Tue Jun 18 00:00:00 EDT 2019
@article{osti_1881422,
title = {Up/Down Impurity Density Asymmetries in C-Mod Plasmas},
author = {Rice, J. E. and Reinke, M. L. and Cao, N. and Hughes, J. W. and Ashbourn, J. M. A. and Ernst, D. R. and Hubbard, A. E. and Irby, J. H.},
abstractNote = {Brightness profiles of x-ray emission from H-like Ar17+ exhibit a distinct up/down asymmetry under certain operating conditions in C-Mod plasmas, indicating that impurity densities are not constant on flux surfaces with r/a between ~0.8 and ~0.95. In L- and I-mode plasmas, there is an x-ray brightness excess, up to a factor of 8, on the side opposite to the ion BxgradB drift direction. This effect is not observed in H-mode plasmas, presumably due to edge impurity transport being dominated by a strong inward pinch, which is absent in L- and I-mode. The magnitude of the asymmetry in L- and I-mode decreases with increasing plasma current, similar to the observed decrease in radial impurity diffusivity. In I-mode, where the codependence between electron density and temperature can be broken with ICRF heating power, the asymmetry magnitude is found to decrease with increasing density and with increasing edge temperature at fixed density. These measurements exhibit some qualitative features of neo-classical expectations but the observed asymmetry magnitude is much larger than predicted and some scalings with plasma parameters are not seen. The up/down asymmetry appears to be largest when the cross field impurity diffusivity is the highest.},
doi = {10.7910/DVN/XCNLJZ},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {6}
}

Works referencing / citing this record:

Up/down impurity density asymmetries in C-Mod plasmas
journal, September 2018