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Title: Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment

Abstract

Experiments conducted in high-performance 1.0 and 1.2 MA 6 MW NBI-heated H-mode discharges with a high magnetic flux expansion radiative divertor in NSTX demonstrate that significant divertor peak heat flux reduction and access to detachment may be facilitated naturally in a highly shaped spherical torus (ST) configuration. Improved plasma performance with high beta(t) = 15-25%, a high bootstrap current fraction f(BS) = 45-50%, longer plasma pulses and an H-mode regime with smaller ELMs has been achieved in the strongly shaped lower single null configuration with elongation kappa = 2.2-2.4 and triangularity delta = 0.7-0.8. Divertor peak heat fluxes were reduced from 6-12 to 0.5-2 MW m(-2) in ELMy H-mode discharges using the inherently high magnetic flux expansion f(m) = 15-25 and the partial detachment of the outer strike point at several D-2 injection rates. A good core confinement and pedestal characteristics were maintained, while the core carbon concentration and the associated Z(eff) were reduced. The partially detached divertor regime was characterized by an increase in divertor radiated power, a reduction in ion flux to the plate and a large neutral compression ratio. Spectroscopic measurements indicated the formation of a high-density, low-temperature region adjacent to the outer strike point, where substantialmore » increases in the volume recombination rate and C II, CIII emission rates were measured.« less

Authors:
 [1];  [2];  [3];  [3];  [3];  [4];  [3];  [3];  [2];  [3];  [3];  [3];  [3]
  1. Lawrence Livermore National Laboratory (LLNL)
  2. Oak Ridge National Laboratory (ORNL)
  3. Princeton Plasma Physics Laboratory (PPPL)
  4. University of Washington, Seattle
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1015721
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 49; Journal Issue: 9; Journal ID: ISSN 0029--5515
Country of Publication:
United States
Language:
English

Citation Formats

Soukhanovskii, V. A., Maingi, R., Gates, D. A., Menard, J., Paul, S. F., Raman, R., Roquemore, A. L., Bell, R. E., Bush, C. E., Kaita, R., Kugel, H., LeBlanc, B, and Mueller, D. Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment. United States: N. p., 2009. Web. doi:10.1088/0029-5515/49/9/095025.
Soukhanovskii, V. A., Maingi, R., Gates, D. A., Menard, J., Paul, S. F., Raman, R., Roquemore, A. L., Bell, R. E., Bush, C. E., Kaita, R., Kugel, H., LeBlanc, B, & Mueller, D. Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment. United States. https://doi.org/10.1088/0029-5515/49/9/095025
Soukhanovskii, V. A., Maingi, R., Gates, D. A., Menard, J., Paul, S. F., Raman, R., Roquemore, A. L., Bell, R. E., Bush, C. E., Kaita, R., Kugel, H., LeBlanc, B, and Mueller, D. Thu . "Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment". United States. https://doi.org/10.1088/0029-5515/49/9/095025.
@article{osti_1015721,
title = {Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment},
author = {Soukhanovskii, V. A. and Maingi, R. and Gates, D. A. and Menard, J. and Paul, S. F. and Raman, R. and Roquemore, A. L. and Bell, R. E. and Bush, C. E. and Kaita, R. and Kugel, H. and LeBlanc, B and Mueller, D.},
abstractNote = {Experiments conducted in high-performance 1.0 and 1.2 MA 6 MW NBI-heated H-mode discharges with a high magnetic flux expansion radiative divertor in NSTX demonstrate that significant divertor peak heat flux reduction and access to detachment may be facilitated naturally in a highly shaped spherical torus (ST) configuration. Improved plasma performance with high beta(t) = 15-25%, a high bootstrap current fraction f(BS) = 45-50%, longer plasma pulses and an H-mode regime with smaller ELMs has been achieved in the strongly shaped lower single null configuration with elongation kappa = 2.2-2.4 and triangularity delta = 0.7-0.8. Divertor peak heat fluxes were reduced from 6-12 to 0.5-2 MW m(-2) in ELMy H-mode discharges using the inherently high magnetic flux expansion f(m) = 15-25 and the partial detachment of the outer strike point at several D-2 injection rates. A good core confinement and pedestal characteristics were maintained, while the core carbon concentration and the associated Z(eff) were reduced. The partially detached divertor regime was characterized by an increase in divertor radiated power, a reduction in ion flux to the plate and a large neutral compression ratio. Spectroscopic measurements indicated the formation of a high-density, low-temperature region adjacent to the outer strike point, where substantial increases in the volume recombination rate and C II, CIII emission rates were measured.},
doi = {10.1088/0029-5515/49/9/095025},
url = {https://www.osti.gov/biblio/1015721}, journal = {Nuclear Fusion},
issn = {0029--5515},
number = 9,
volume = 49,
place = {United States},
year = {2009},
month = {1}
}