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Title: Reduction of low-Z impurities during plasma start-up

Abstract

Reduction of low-Z impurities is essential during the plasma start-up in tokamaks. For plasma start-up using the method of Coaxial Helicity Injection (CHI) it has been found here that conventional wall conditioning methods have been inadequate to generate a plasma with acceptably low levels of low-Z impurities. NSTX has now used a new combination of techniques to improve CHI start-up performance. These are the use of high-current discharge cleaning of the lower divertor surfaces, which function as the CHI electrodes, to remove loosely bound impurities, controlling the poloidal magnetic field to avoid plasma wall contact and the use of evaporated lithium coatings of the electrodes and other plasma-facing surfaces. Together, these techniques have enabled significant improvement in NSTX CHI performance leading to a saving of central solenoid flux and the first observation of electron temperatures during CHI exceeding the oxygen radiation barrier temperature.

Authors:
 [1];  [1];  [2];  [2];  [2];  [2];  [2];  [2];  [3]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Univ. of Washington, Seattle, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1524725
Report Number(s):
LLNL-JRNL-434313
Journal ID: ISSN 0022-3115; 402108
Grant/Contract Number:  
AC52-07NA27344; AC02-09CH11466; FG03-96ER54361; FG02-99ER54519
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 415; Journal Issue: S1; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Raman, R., Jarboe, T. R., Mueller, D., Nelson, B. A., Bell, M. G., Kugel, H. W., LeBlanc, B., Roquemore, L., and Soukhanovskii, V. Reduction of low-Z impurities during plasma start-up. United States: N. p., 2010. Web. doi:10.1016/j.jnucmat.2010.11.077.
Raman, R., Jarboe, T. R., Mueller, D., Nelson, B. A., Bell, M. G., Kugel, H. W., LeBlanc, B., Roquemore, L., & Soukhanovskii, V. Reduction of low-Z impurities during plasma start-up. United States. doi:10.1016/j.jnucmat.2010.11.077.
Raman, R., Jarboe, T. R., Mueller, D., Nelson, B. A., Bell, M. G., Kugel, H. W., LeBlanc, B., Roquemore, L., and Soukhanovskii, V. Sat . "Reduction of low-Z impurities during plasma start-up". United States. doi:10.1016/j.jnucmat.2010.11.077. https://www.osti.gov/servlets/purl/1524725.
@article{osti_1524725,
title = {Reduction of low-Z impurities during plasma start-up},
author = {Raman, R. and Jarboe, T. R. and Mueller, D. and Nelson, B. A. and Bell, M. G. and Kugel, H. W. and LeBlanc, B. and Roquemore, L. and Soukhanovskii, V.},
abstractNote = {Reduction of low-Z impurities is essential during the plasma start-up in tokamaks. For plasma start-up using the method of Coaxial Helicity Injection (CHI) it has been found here that conventional wall conditioning methods have been inadequate to generate a plasma with acceptably low levels of low-Z impurities. NSTX has now used a new combination of techniques to improve CHI start-up performance. These are the use of high-current discharge cleaning of the lower divertor surfaces, which function as the CHI electrodes, to remove loosely bound impurities, controlling the poloidal magnetic field to avoid plasma wall contact and the use of evaporated lithium coatings of the electrodes and other plasma-facing surfaces. Together, these techniques have enabled significant improvement in NSTX CHI performance leading to a saving of central solenoid flux and the first observation of electron temperatures during CHI exceeding the oxygen radiation barrier temperature.},
doi = {10.1016/j.jnucmat.2010.11.077},
journal = {Journal of Nuclear Materials},
number = S1,
volume = 415,
place = {United States},
year = {2010},
month = {12}
}

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