Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod

Tolman, E. A.; Hughes, J. W.; Wolfe, S. M.; Wukitch, S. J.; LaBombard, B.; Hubbard, A. E.; Marmar, E. S.; Snyder, P. B.; Schmidtmayr, M.

doi:10.7910/DVN/QBOO7B

Title: Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod

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Abstract

Recent Alcator C-Mod experiments have explored access to and characteristics of H-modes at magnetic fields approaching 8 T, the highest field achieved to date in a diverted tokamak. The H-modes originated from L-mode densities ranging from $$1.1 \times 10^{20} m^{-3}$$ to $$2.8 \times 10^{20} m^{-3}$$, allowing insight into the density dependence of the H-mode power threshold at high magnetic field. This dependence is compared to predictions from the ITPA scaling law (\cite{martin2008power}), finding that the law is approximately accurate at 7.8 T. However, the law underpredicted the high density H-mode threshold at lower magnetic field in previous C-Mod experiments (\cite{ma2012scaling}), \hl{suggesting that the overall dependence of the threshold on magnetic field is weaker than predicted by the scaling law.} The threshold data at 7.8 T also indicates that the onset of a low density branch at this magnetic field on C-Mod occurs below $$1.4 \times 10^{20} m^{-3}$$, which is lower than predicted by an existing model for low density branch onset. The H-modes achieved steady-state densities ranging from $$2.3 \times 10^{20} m^{-3}$$ to $$4.4 \times 10^{20} m^{-3}$$, and higher transient densities, and had values of $$q_{95}$$ from 3.3 to 6.0. This parameter range allowed the achievement of all three types of H-mode routinely observed at lower magnetic field on C-Mod: the stationary, ELM-suppressed enhanced D-alpha (EDA) regime, seen at high densities and high values of $$q_{95}$$; the nonstationary ELM-free regime, seen at lower densities and values of $$q_{95}$$; and the ELMy regime, seen at low density, moderate $$q_{95}$$, and specialized plasma shape. The parameter space in which these regimes occur at 7.8 T is consistent with lower magnetic field experience. Pressure pedestal height at 7.8 T is compared to EPED \cite{snyder2009development, snyder2011first} predictions, and a scaling law for EDA density pedestal height developed between 4.5 and 6.0 T is updated to include fields from 2.7 T to 7.8 T. Overall, this analysis increases confidence in the use of low magnetic field experience to predict some elements of high magnetic field tokamak behavior.

Authors:

Tolman, E. A.; Hughes, J. W.; Wolfe, S. M.; Wukitch, S. J.; LaBombard, B.; Hubbard, A. E.; Marmar, E. S.; Snyder, P. B.; Schmidtmayr, M.

OSTI

Publication Date:: Tue Oct 16 00:00:00 EDT 2018

DOE Contract Number:: FC02-99ER54512; SC0014264

Research Org.:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Sponsoring Org.:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

OSTI Identifier:: 1879092

DOI:: https://doi.org/10.7910/DVN/QBOO7B

Citation Formats


                    Tolman, E. A., Hughes, J. W., Wolfe, S. M., Wukitch, S. J., LaBombard, B., Hubbard, A. E., Marmar, E. S., Snyder, P. B., and Schmidtmayr, M. Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod.  United States: N. p., 2018. 
        Web.  doi:10.7910/DVN/QBOO7B.

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                    Tolman, E. A., Hughes, J. W., Wolfe, S. M., Wukitch, S. J., LaBombard, B., Hubbard, A. E., Marmar, E. S., Snyder, P. B., & Schmidtmayr, M. Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod.  United States.  doi:https://doi.org/10.7910/DVN/QBOO7B

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                    Tolman, E. A., Hughes, J. W., Wolfe, S. M., Wukitch, S. J., LaBombard, B., Hubbard, A. E., Marmar, E. S., Snyder, P. B., and Schmidtmayr, M. 2018.  
"Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod".  United States.  doi:https://doi.org/10.7910/DVN/QBOO7B.  https://www.osti.gov/servlets/purl/1879092. Pub date:Tue Oct 16 00:00:00 EDT 2018

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@article{osti_1879092,

  title        = {Influence of High Magnetic Field on Access to Stationary H-modes and Pedestal Characteristics in Alcator C-Mod},

  author       = {Tolman, E. A. and Hughes, J. W. and Wolfe, S. M. and Wukitch, S. J. and LaBombard, B. and Hubbard, A. E. and Marmar, E. S. and Snyder, P. B. and Schmidtmayr, M.},

  abstractNote = {Recent Alcator C-Mod experiments have explored access to and characteristics of H-modes at magnetic fields approaching 8 T, the highest field achieved to date in a diverted tokamak. The H-modes originated from L-mode densities ranging from $1.1 \times 10^{20} m^{-3}$ to $2.8 \times 10^{20} m^{-3}$, allowing insight into the density dependence of the H-mode power threshold at high magnetic field. This dependence is compared to predictions from the ITPA scaling law (\cite{martin2008power}), finding that the law is approximately accurate at 7.8 T. However, the law underpredicted the high density H-mode threshold at lower magnetic field in previous C-Mod experiments (\cite{ma2012scaling}), \hl{suggesting that the overall dependence of the threshold on magnetic field is weaker than predicted by the scaling law.} The threshold data at 7.8 T also indicates that the onset of a low density branch at this magnetic field on C-Mod occurs below $1.4 \times 10^{20} m^{-3}$, which is lower than predicted by an existing model for low density branch onset. The H-modes achieved steady-state densities ranging from $2.3 \times 10^{20} m^{-3}$ to $4.4 \times 10^{20} m^{-3}$, and higher transient densities, and had values of $q_{95}$ from 3.3 to 6.0. This parameter range allowed the achievement of all three types of H-mode routinely observed at lower magnetic field on C-Mod: the stationary, ELM-suppressed enhanced D-alpha (EDA) regime, seen at high densities and high values of $q_{95}$; the nonstationary ELM-free regime, seen at lower densities and values of $q_{95}$; and the ELMy regime, seen at low density, moderate $q_{95}$, and specialized plasma shape. The parameter space in which these regimes occur at 7.8 T is consistent with lower magnetic field experience. Pressure pedestal height at 7.8 T is compared to EPED \cite{snyder2009development, snyder2011first} predictions, and a scaling law for EDA density pedestal height developed between 4.5 and 6.0 T is updated to include fields from 2.7 T to 7.8 T. Overall, this analysis increases confidence in the use of low magnetic field experience to predict some elements of high magnetic field tokamak behavior.},

  doi          = {10.7910/DVN/QBOO7B},

  journal      = {},

  number       = ,

  volume       = ,

  place        = {United States},

  year         = {Tue Oct 16 00:00:00 EDT 2018},

  month        = {Tue Oct 16 00:00:00 EDT 2018}

}

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DOI: https://doi.org/10.7910/DVN/QBOO7B

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