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Title: Enhanced H-mode pedestals with lithium injection in DIII-D

Abstract

Periods of edge localized mode (ELM)-free H-mode with increased pedestal pressure and width were observed in the DIII-D tokamak when density fluctuations localized to the region near the separatrix were present. Injection of a powder of 45 m diameter lithium particles increased the duration of the enhanced pedestal phases to up to 350 ms, and also increased the likelihood of a transition to the enhanced phase. Lithium injection at a level sufficient for triggering the extended enhanced phases resulted in significant lithium in the plasma core, but carbon and other higher Z impurities as well as radiated power levels were reduced. Recycling of the working deuterium gas appeared unaffected by this level of lithium injection. The ion scale, k θϱ s ~ 0.1 0.2, density fluctuations propagated in the electron drift direction with f ~ 80 kHz and occurred in bursts every ~1 ms. The fluctuation bursts correlated with plasma loss resulting in a flattening of the pressure profile in a region near the separatrix. This localized flattening allowed higher overall pedestal pressure at the peeling ballooning stability limit and higher pressure than expected under the EPED model due to reduction of the pressure gradient below the 'ballooning critical profile'.more » Furthermore, reduction of the ion pressure by lithium dilution may contribute to the long ELM-free periods.« less

Authors:
 [1];  [1];  [2];  [3];  [3];  [3];  [4];  [5];  [5];  [3];  [6];  [5];  [2];  [1]
  1. General Atomics, San Diego, CA (United States)
  2. Univ. of Wisconsin, Madison, WI (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Univ. of California San Diego, La Jolla, CA (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1286919
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 6; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Osborne, T. H., Jackson, G. L., Yan, Z., Maingi, R., Mansfield, D. K., Grierson, Brian A., Chrobak, C. P., McLean, A. G., Allen, Steve L., Battaglia, D. J., Briesemeister, Alexis R., Fenstermacher, M. E., Mckee, G. R., and Snyder, P. B. Enhanced H-mode pedestals with lithium injection in DIII-D. United States: N. p., 2015. Web. doi:10.1088/0029-5515/55/6/063018.
Osborne, T. H., Jackson, G. L., Yan, Z., Maingi, R., Mansfield, D. K., Grierson, Brian A., Chrobak, C. P., McLean, A. G., Allen, Steve L., Battaglia, D. J., Briesemeister, Alexis R., Fenstermacher, M. E., Mckee, G. R., & Snyder, P. B. Enhanced H-mode pedestals with lithium injection in DIII-D. United States. doi:10.1088/0029-5515/55/6/063018.
Osborne, T. H., Jackson, G. L., Yan, Z., Maingi, R., Mansfield, D. K., Grierson, Brian A., Chrobak, C. P., McLean, A. G., Allen, Steve L., Battaglia, D. J., Briesemeister, Alexis R., Fenstermacher, M. E., Mckee, G. R., and Snyder, P. B. Fri . "Enhanced H-mode pedestals with lithium injection in DIII-D". United States. doi:10.1088/0029-5515/55/6/063018.
@article{osti_1286919,
title = {Enhanced H-mode pedestals with lithium injection in DIII-D},
author = {Osborne, T. H. and Jackson, G. L. and Yan, Z. and Maingi, R. and Mansfield, D. K. and Grierson, Brian A. and Chrobak, C. P. and McLean, A. G. and Allen, Steve L. and Battaglia, D. J. and Briesemeister, Alexis R. and Fenstermacher, M. E. and Mckee, G. R. and Snyder, P. B.},
abstractNote = {Periods of edge localized mode (ELM)-free H-mode with increased pedestal pressure and width were observed in the DIII-D tokamak when density fluctuations localized to the region near the separatrix were present. Injection of a powder of 45 m diameter lithium particles increased the duration of the enhanced pedestal phases to up to 350 ms, and also increased the likelihood of a transition to the enhanced phase. Lithium injection at a level sufficient for triggering the extended enhanced phases resulted in significant lithium in the plasma core, but carbon and other higher Z impurities as well as radiated power levels were reduced. Recycling of the working deuterium gas appeared unaffected by this level of lithium injection. The ion scale, kθϱs ~ 0.1 0.2, density fluctuations propagated in the electron drift direction with f ~ 80 kHz and occurred in bursts every ~1 ms. The fluctuation bursts correlated with plasma loss resulting in a flattening of the pressure profile in a region near the separatrix. This localized flattening allowed higher overall pedestal pressure at the peeling ballooning stability limit and higher pressure than expected under the EPED model due to reduction of the pressure gradient below the 'ballooning critical profile'. Furthermore, reduction of the ion pressure by lithium dilution may contribute to the long ELM-free periods.},
doi = {10.1088/0029-5515/55/6/063018},
journal = {Nuclear Fusion},
issn = {0029-5515},
number = 6,
volume = 55,
place = {United States},
year = {2015},
month = {5}
}