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Title: Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D

Abstract

Comparison between an open divertor and a more-closed divertor in DIII-D demonstrates detachment at an up to 40% lower pedestal density (ne,ped) in the closed divertor, due to a combination of decreased fueling of the pedestal and increased dissipation in the scrape off layer (SOL) in the closed divertor, both resulting from increased neutral trapping in the divertor. Predicting whether the relationship between divertor closure and detachment will hold for an opaque SOL, in which the contribution of ionizing neutrals to fueling the pedestal is lessened, requires separating out the different mechanisms contributing to the density difference at detachment. A series of experiments on DIII-D characterizes matched discharges using various divertor configurations to isolate the effects of divertor closure. These experiments show detachment at up to 25% lower ne,sep in the closed divertor than the open, supported by simulations showing increased neutral trapping, and hence increased dissipation, in the closed divertor. A difference in ne,ped/ne,sep is also seen: for matched ne,sep, the closed divertor has up to 20% lower ne,ped, consistent with modeling showing a smaller ionization fraction inside the separatrix in this case. Understanding how these pieces fit together will help in develop of predictive models of pedestal densitymore » and detached divertors compatible with a high-performance core.« less

Authors:
 [1]; ORCiD logo [1];  [1]; ORCiD logo [1];  [2]; ORCiD logo [3];  [1];  [4]
  1. General Atomics, San Diego, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1608790
Alternate Identifier(s):
OSTI ID: 1604236; OSTI ID: 1648965
Grant/Contract Number:  
FC02-04ER54698; AC52-07NA27344; AC05-00OR22725; AC04-94AL85000
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 27; Journal Issue: 3; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Moser, A. L., Casali, L., Covele, B. M., Leonard, A. W., McLean, A. G., Shafer, M. W., Wang, H. Q., and Watkins, J. G. Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D. United States: N. p., 2020. Web. doi:10.1063/1.5109027.
Moser, A. L., Casali, L., Covele, B. M., Leonard, A. W., McLean, A. G., Shafer, M. W., Wang, H. Q., & Watkins, J. G. Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D. United States. doi:https://doi.org/10.1063/1.5109027
Moser, A. L., Casali, L., Covele, B. M., Leonard, A. W., McLean, A. G., Shafer, M. W., Wang, H. Q., and Watkins, J. G. Thu . "Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D". United States. doi:https://doi.org/10.1063/1.5109027. https://www.osti.gov/servlets/purl/1608790.
@article{osti_1608790,
title = {Separating divertor closure effects on divertor detachment and pedestal shape in DIII-D},
author = {Moser, A. L. and Casali, L. and Covele, B. M. and Leonard, A. W. and McLean, A. G. and Shafer, M. W. and Wang, H. Q. and Watkins, J. G.},
abstractNote = {Comparison between an open divertor and a more-closed divertor in DIII-D demonstrates detachment at an up to 40% lower pedestal density (ne,ped) in the closed divertor, due to a combination of decreased fueling of the pedestal and increased dissipation in the scrape off layer (SOL) in the closed divertor, both resulting from increased neutral trapping in the divertor. Predicting whether the relationship between divertor closure and detachment will hold for an opaque SOL, in which the contribution of ionizing neutrals to fueling the pedestal is lessened, requires separating out the different mechanisms contributing to the density difference at detachment. A series of experiments on DIII-D characterizes matched discharges using various divertor configurations to isolate the effects of divertor closure. These experiments show detachment at up to 25% lower ne,sep in the closed divertor than the open, supported by simulations showing increased neutral trapping, and hence increased dissipation, in the closed divertor. A difference in ne,ped/ne,sep is also seen: for matched ne,sep, the closed divertor has up to 20% lower ne,ped, consistent with modeling showing a smaller ionization fraction inside the separatrix in this case. Understanding how these pieces fit together will help in develop of predictive models of pedestal density and detached divertors compatible with a high-performance core.},
doi = {10.1063/1.5109027},
journal = {Physics of Plasmas},
number = 3,
volume = 27,
place = {United States},
year = {2020},
month = {3}
}

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