The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod

Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

doi:10.7910/DVN/O7X1HW

Title: The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod

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Abstract

Management of power exhaust will be a crucial task for tokamak fusion reactors. Reactor concepts are often proposed with double-null divertors, i.e. having two magnetic separatrices in an up-down symmetric configuration. This arrangement is potentially advantageous since the majority of the tokamak exhaust power tends to flow to the outer pair of divertor legs at large major radius, where the geometry is favorable for spreading the heat over a large surface area and there is more room for advanced divertor configurations. Despite the importance, there have been relatively few studies of divertor power sharing in near double null configurations and no studies at the poloidal magnetic fields and scrape-off layer power widths anticipated for a reactor. Motivated by this need we have undertaken a systematic study on Alcator C-Mod, examining the effect of magnetic flux balance on the power sharing among the four divertor legs in near double-null plasmas. Ohmic L-modes at three values of plasma current and ICRF-heated enhanced D-alpha (EDA) H-modes and I-modes at a single value of plasma current are explored, producing poloidal magnetic fields of 0.42, 0.62 and 0.85 Tesla. For Ohmic L-modes and ICRF-heated EDA H-modes, we find that the point of equal power sharingmore »« less

Authors:

Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; OSTI
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Publication Date:: Thu Sep 06 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:: 1878531

DOI:: https://doi.org/10.7910/DVN/O7X1HW

Citation Formats


                    Brunner, D., Kuang, A. Q., LaBombard, B., and Terry, J. L. The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod.  United States: N. p., 2018. 
        Web.  doi:10.7910/DVN/O7X1HW.

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                    Brunner, D., Kuang, A. Q., LaBombard, B., & Terry, J. L. The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod.  United States.  doi:https://doi.org/10.7910/DVN/O7X1HW

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                    Brunner, D., Kuang, A. Q., LaBombard, B., and Terry, J. L. 2018.  
"The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod".  United States.  doi:https://doi.org/10.7910/DVN/O7X1HW.  https://www.osti.gov/servlets/purl/1878531. Pub date:Thu Sep 06 00:00:00 EDT 2018

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@article{osti_1878531,

  title        = {The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod},

  author       = {Brunner, D. and Kuang, A. Q. and LaBombard, B. and Terry, J. L.},

  abstractNote = {Management of power exhaust will be a crucial task for tokamak fusion reactors. Reactor concepts are often proposed with double-null divertors, i.e. having two magnetic separatrices in an up-down symmetric configuration. This arrangement is potentially advantageous since the majority of the tokamak exhaust power tends to flow to the outer pair of divertor legs at large major radius, where the geometry is favorable for spreading the heat over a large surface area and there is more room for advanced divertor configurations. Despite the importance, there have been relatively few studies of divertor power sharing in near double null configurations and no studies at the poloidal magnetic fields and scrape-off layer power widths anticipated for a reactor. Motivated by this need we have undertaken a systematic study on Alcator C-Mod, examining the effect of magnetic flux balance on the power sharing among the four divertor legs in near double-null plasmas. Ohmic L-modes at three values of plasma current and ICRF-heated enhanced D-alpha (EDA) H-modes and I-modes at a single value of plasma current are explored, producing poloidal magnetic fields of 0.42, 0.62 and 0.85 Tesla. For Ohmic L-modes and ICRF-heated EDA H-modes, we find that the point of equal power sharing between upper and lower divertors occurs remarkably close to a balanced double null. Power sharing amongst the outer (upper versus lower) and inner (upper versus lower) pairs of divertors can be described in terms of a logistic function of magnetic flux balance, consistent with heat flux mapping along magnetic field lines to the outer midplane. Power sharing between inner and outer legs is found to follow a Gaussian-like function of magnetic flux balance with non-zero power to the inner divertors at double null. The overall behavior of H-modes operated near double null and for I-modes operating to within one heat flux e-folding of double null are found similar to Ohmic L-modes, with a significant reduction of power on the inner divertor legs. The results are encapsulated in terms of empirically-informed analytic functions of magnetic flux balance. When combined with magnetic equilibrium control system specifications, these relationships can be used to specify the power flux handling requirements for each of the four divertor target plates.},

  doi          = {10.7910/DVN/O7X1HW},

  journal      = {},

  number       = ,

  volume       = ,

  place        = {United States},

  year         = {Thu Sep 06 00:00:00 EDT 2018},

  month        = {Thu Sep 06 00:00:00 EDT 2018}

}

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DOI: https://doi.org/10.7910/DVN/O7X1HW

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