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Title: Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D

Abstract

Impurity seeding studies in the slot divertor (SAS) at DIII-D have revealed a strong relationship between the detachment onset and pedestal characteristics with both target geometry and impurity species. N2 seeding in the slot has led to the first simultaneous observation of detachment on the entire suite of boundary diagnostics viewing the SAS without degradation of core confinement. SOLPS-ITER simulations with D+C+N, full cross-field drifts and n-n collisions activated are performed for the first time in DIII-D to interpret the behavior. This illustrates a strong effect of divertor configuration and plasma drifts on the recycling source distribution with significant consequences on plasma flows. Flow reversal is found for both main ions and impurities affecting strongly the impurity transport and providing an explanation for the observed dependence on strike point location of the detachment onset and impurity leakage found in the experiments. Matched discharges with either nitrogen or neon injection show that while nitrogen does not significantly affect the pedestal, neon leads to increased pedestal pressure gradient and improved pedestal stability. Little nitrogen penetrates in the core, but a great amount of neon is found in the pedestal consistent with the different ionization potentials of the two impurities. This research demonstratesmore » that neutral and impurity distributions in the divertor can be controlled through variations in strike point locations in a fixed baffle structure. Divertor geometry combined with impurity seeding enables mitigated divertor heat flux balancing core contamination and thus leading to enhanced divertor dissipation and improved core-edge compatibility which are essential for ITER and for future fusion reactors.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2];  [3];  [4];  [5];  [6];  [1];  [7]
  1. General Atomics, San Diego, CA (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Washington, Seattle, WA (United States)
  5. Univ. of Tennessee, Knoxville, TN (United States)
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  7. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1632683
Alternate Identifier(s):
OSTI ID: 1631497; OSTI ID: 1648972
Report Number(s):
DOE-GA-54698
Journal ID: ISSN 1070-664X
Grant/Contract Number:  
FC02-04ER54698; AC52-07NA27344; AC02-09CH11466; AC05-00OR22725; NA0003525
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 27; Journal Issue: 6; Conference: 61. Annual Meeting of the APS Division of Plasma Physics, Fort Lauderdale, FL (United States), 21-25 Oct 2019; 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

Casali, L., Osborne, T. H., Grierson, B. A., McLean, A. G., Meier, E. T., Ren, J., Shafer, M. W., Wang, H., and Watkins, J. G. Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D. United States: N. p., 2020. Web. doi:10.1063/1.5144693.
Casali, L., Osborne, T. H., Grierson, B. A., McLean, A. G., Meier, E. T., Ren, J., Shafer, M. W., Wang, H., & Watkins, J. G. Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D. United States. doi:https://doi.org/10.1063/1.5144693
Casali, L., Osborne, T. H., Grierson, B. A., McLean, A. G., Meier, E. T., Ren, J., Shafer, M. W., Wang, H., and Watkins, J. G. Tue . "Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D". United States. doi:https://doi.org/10.1063/1.5144693.
@article{osti_1632683,
title = {Improved core-edge compatibility using impurity seeding in the small angle slot (SAS) divertor at DIII-D},
author = {Casali, L. and Osborne, T. H. and Grierson, B. A. and McLean, A. G. and Meier, E. T. and Ren, J. and Shafer, M. W. and Wang, H. and Watkins, J. G.},
abstractNote = {Impurity seeding studies in the slot divertor (SAS) at DIII-D have revealed a strong relationship between the detachment onset and pedestal characteristics with both target geometry and impurity species. N2 seeding in the slot has led to the first simultaneous observation of detachment on the entire suite of boundary diagnostics viewing the SAS without degradation of core confinement. SOLPS-ITER simulations with D+C+N, full cross-field drifts and n-n collisions activated are performed for the first time in DIII-D to interpret the behavior. This illustrates a strong effect of divertor configuration and plasma drifts on the recycling source distribution with significant consequences on plasma flows. Flow reversal is found for both main ions and impurities affecting strongly the impurity transport and providing an explanation for the observed dependence on strike point location of the detachment onset and impurity leakage found in the experiments. Matched discharges with either nitrogen or neon injection show that while nitrogen does not significantly affect the pedestal, neon leads to increased pedestal pressure gradient and improved pedestal stability. Little nitrogen penetrates in the core, but a great amount of neon is found in the pedestal consistent with the different ionization potentials of the two impurities. This research demonstrates that neutral and impurity distributions in the divertor can be controlled through variations in strike point locations in a fixed baffle structure. Divertor geometry combined with impurity seeding enables mitigated divertor heat flux balancing core contamination and thus leading to enhanced divertor dissipation and improved core-edge compatibility which are essential for ITER and for future fusion reactors.},
doi = {10.1063/1.5144693},
journal = {Physics of Plasmas},
number = 6,
volume = 27,
place = {United States},
year = {2020},
month = {6}
}

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