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Title: Determination of carbon release mechanisms in the DIII-D divertors from analysis of C I line profiles

Abstract

During typical operation of the DIII-D tokamak, physical and chemical sputtering are the most important mechanisms for release of carbon at the divertor targets [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. Modeling of C I spectral line profiles is discussed as a technique for evaluating the relative contribution of each process and is applied to several types of discharges. The line shapes are symmetric and have shifts of about -0.03 A ring if they are produced solely from molecular dissociation, but they exhibit distinct asymmetries and shifts approaching -0.20 A ring if generated by physical sputtering. Modeled profiles must, in general, take account of both mechanisms in order to match experimental data. An alternate approach to distinguishing between the two processes, which relies on the relative intensities of C I, CD, and C{sub 2} emissions, is examined in light of conclusions drawn from the line-shape analysis.

Authors:
; ; ;  [1];  [2];  [3]
  1. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8072 (United States)
  2. (United States)
  3. (Canada)
Publication Date:
OSTI Identifier:
20960105
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2431352; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASYMMETRY; CARBON; DIVERTORS; DOUBLET-3 DEVICE; PLASMA; PLASMA CONFINEMENT; PLASMA IMPURITIES; PLASMA SIMULATION; THERMONUCLEAR REACTORS; WALL EFFECTS

Citation Formats

Isler, R. C., Brooks, N. H., West, W. P., McLean, A. G., General Atomics, San Diego, California 92186-5068, and University of Toronto Institute for Aerospace Studies, Toronto, M3H5T6. Determination of carbon release mechanisms in the DIII-D divertors from analysis of C I line profiles. United States: N. p., 2007. Web. doi:10.1063/1.2431352.
Isler, R. C., Brooks, N. H., West, W. P., McLean, A. G., General Atomics, San Diego, California 92186-5068, & University of Toronto Institute for Aerospace Studies, Toronto, M3H5T6. Determination of carbon release mechanisms in the DIII-D divertors from analysis of C I line profiles. United States. doi:10.1063/1.2431352.
Isler, R. C., Brooks, N. H., West, W. P., McLean, A. G., General Atomics, San Diego, California 92186-5068, and University of Toronto Institute for Aerospace Studies, Toronto, M3H5T6. Mon . "Determination of carbon release mechanisms in the DIII-D divertors from analysis of C I line profiles". United States. doi:10.1063/1.2431352.
@article{osti_20960105,
title = {Determination of carbon release mechanisms in the DIII-D divertors from analysis of C I line profiles},
author = {Isler, R. C. and Brooks, N. H. and West, W. P. and McLean, A. G. and General Atomics, San Diego, California 92186-5068 and University of Toronto Institute for Aerospace Studies, Toronto, M3H5T6},
abstractNote = {During typical operation of the DIII-D tokamak, physical and chemical sputtering are the most important mechanisms for release of carbon at the divertor targets [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. Modeling of C I spectral line profiles is discussed as a technique for evaluating the relative contribution of each process and is applied to several types of discharges. The line shapes are symmetric and have shifts of about -0.03 A ring if they are produced solely from molecular dissociation, but they exhibit distinct asymmetries and shifts approaching -0.20 A ring if generated by physical sputtering. Modeled profiles must, in general, take account of both mechanisms in order to match experimental data. An alternate approach to distinguishing between the two processes, which relies on the relative intensities of C I, CD, and C{sub 2} emissions, is examined in light of conclusions drawn from the line-shape analysis.},
doi = {10.1063/1.2431352},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • During typical operation of the DIII-D tokamak, physical and chemical sputtering are the most important mechanisms for release of carbon at the divertor targets [Nuclear Fusion 42 614 (2002)]. Modeling of C I spectral line profiles is discussed as a technique for evaluating the relative contribution of each mechanism and is applied to several types of DIII-D discharges. The line shapes are symmetric and have shifts of about -0.03 if they are produced solely from molecular dissociation, but they exhibit distinct asymmetries and shifts approaching -0.20 if generated by physical sputtering. Modeled profiles must, in general, take account of bothmore » mechanisms in order to match experimental data. An alternate approach to distinguishing between the two processes, which relies on the relative intensities of C I, CD, and C2 emissions, is examined in light of conclusions drawn from the line-shape analysis.« less
  • The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C{sub 2} under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discriminationmore » of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C{sub 2} influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma.« less
  • High precision measurements of the vapor pressure differences between some deuterated benzenes B-d/sub x/ (x=1, para-2, and 6) and protio benzene B-d/sub 0/; between para- and ortho-, and para- and meta-dideuterobenzene; and between perdeuterocyclohexane C-d/sub 12/ and protiocyclohexane C-d/sub 0/ were made from near the freezing point to the normal boiling point. The data are best represented as the logarithmic ratios ln R (d/sub 6/) =ln (P/sub d/0/P/sub d/6) =1226.5/T/sup 2/-12.178/T, ln R (para/ortho) =ln (P/sub parahyphend/2/P/sub orthohyphend/2) =2.6/T/sup 2/, and ln R (para/meta) =ln (P/sub parahyphend/2/P/sub metahyphend/2) =-2.0/T/sup 2/, together with the deviations from the law of the meanmore » ..delta.. (d1) =6-(ln R (d/sub 6/)/lnR (d/sub 1/))=0.177-3.6 x 10/sup -4/t and ..delta.. (d/sub 2hyphenpara/=3-(ln R (d/sub 6/)/ln R (d/sub 2hyphenpara/))=0.028 +1.0 x 10/sup -4/t. The isotope effects are inverse and display significant deviations from the law of the mean. The cyclohexane results are given by ln R (C-d/sub 12/) =-2188.4/T/sup 2/-18.587/T. New measurements of the vapor pressures of benzene--cyclohexane solutions are also reported between 5 and 80 /sup 0/C. The data are in good agreement with the best earlier work. Excess free energies of the equimolar solutions B-h/sub 6//B-d/sub 6/ and C-h/sub 12//C-d/sub 12/ have been measured between 20 and 80 /sup 0/C. Suitable fits to the data yield the following results (30 /sup 0/C); G/sup ex/(B-h/B-d), G/sup ex/(C-h/C-d); H/sup ex/(B-h/B-d),« less
  • A video camera system is described that measures the spatial distribution of visible line emission emitted from the main scrape-off layer (SOL) of plasmas in the DIII-D tokamak. A wide-angle lens installed on an equatorial port and an in-vessel mirror which intercepts part of the lens view provide simultaneous tangential views of the SOL on the low-field and high-field sides of the plasma's equatorial plane. Tomographic reconstruction techniques are used to calculate the 2-D poloidal profiles from the raw data, and 1-D poloidal profiles simulating chordal views of other optical diagnostics from the 2-D profiles. The 2-D profiles can bemore » compared with SOL plasma simulations; the 1-D profiles with measurements from spectroscopic diagnostics. Sample results are presented which elucidate carbon transport in plasmas with toroidally uniform injection of methane and argon transport in disruption mitigation experiments with massive gas jet injection.« less