Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D

doi:10.1088/1741-4326/aaaf99

Title: Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D

Abstract

Numerical simulations of toroidal asymmetries in a tightly baffled small angle slot (SAS) divertor on the DIII-D tokamak show that toroidal asymmetries in divertor closure result in (non-axisymmetric) local onset of detachment within a density window of 10-15% on top of the nominal threshold separatrix density. The SAS divertor is explored at DIII-D for improving access to cold, dissipative/detached divertor conditions. The narrow width of the slot divertor coupled with a small magnetic field line-to-target angle facilitates the buildup of neutral density, thereby increasing radiative and neutrals-related (atoms and molecules) losses in the divertor. Therefore, small changes in the strike point location can be expected to have a large impact on diverter conditions. The combination of misaligned slot structure and non-axisymmetric perturbations to the magnetic field configuration causes the strike point to move along the divertor target plate, possibly leaving the diverter slot at some locations. The latter extreme case essentially introduces an opening in the divertor slot from where recycling neutrals can easily escape, and thereby degrade the performance of the slot divertor. Such a strike point dislocation is approximated by a finite gap in the divertor baffle for which three dimensional edge plasma and neutral gas simulations aremore » performed with the EMC3-EIRENE code.« less

Authors:

Frerichs, H. ^[1]; Schmitz, O. ^[1]; Covele, B. ^[2]; Feng, Y. ^[3]; Guo, H. Y. ^[2]; Hill, D. ^[2]

Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
General Atomics, San Diego, CA (United States)
Max Planck Inst. for Plasma Physics, Heidelberg (Germany)

Publication Date:: 2018-02-28

Research Org.:: General Atomics, San Diego, CA (United States)

Sponsoring Org.:: USDOE

OSTI Identifier:: 1423897

Grant/Contract Number:: FC02-04ER54698; SC0013911

Resource Type:: Accepted Manuscript

Journal Name:: Nuclear Fusion

Additional Journal Information:: Journal Volume: 58; Journal Issue: 5; Journal ID: ISSN 0029-5515

Publisher:: IOP Science

Country of Publication:: United States

Language:: English

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats


                    Frerichs, H., Schmitz, O., Covele, B., Feng, Y., Guo, H. Y., and Hill, D. Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D.  United States: N. p., 2018. 
        Web.  doi:10.1088/1741-4326/aaaf99.

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                    Frerichs, H., Schmitz, O., Covele, B., Feng, Y., Guo, H. Y., & Hill, D. Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D.  United States.  doi:10.1088/1741-4326/aaaf99.

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                    Frerichs, H., Schmitz, O., Covele, B., Feng, Y., Guo, H. Y., and Hill, D. Wed .  
        "Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D".  United States.  doi:10.1088/1741-4326/aaaf99.  https://www.osti.gov/servlets/purl/1423897.

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@article{osti_1423897,

  title        = {Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D},

  author       = {Frerichs, H. and Schmitz, O. and Covele, B. and Feng, Y. and Guo, H. Y. and Hill, D.},

  abstractNote = {Numerical simulations of toroidal asymmetries in a tightly baffled small angle slot (SAS) divertor on the DIII-D tokamak show that toroidal asymmetries in divertor closure result in (non-axisymmetric) local onset of detachment within a density window of 10-15% on top of the nominal threshold separatrix density. The SAS divertor is explored at DIII-D for improving access to cold, dissipative/detached divertor conditions. The narrow width of the slot divertor coupled with a small magnetic field line-to-target angle facilitates the buildup of neutral density, thereby increasing radiative and neutrals-related (atoms and molecules) losses in the divertor. Therefore, small changes in the strike point location can be expected to have a large impact on diverter conditions. The combination of misaligned slot structure and non-axisymmetric perturbations to the magnetic field configuration causes the strike point to move along the divertor target plate, possibly leaving the diverter slot at some locations. The latter extreme case essentially introduces an opening in the divertor slot from where recycling neutrals can easily escape, and thereby degrade the performance of the slot divertor. Such a strike point dislocation is approximated by a finite gap in the divertor baffle for which three dimensional edge plasma and neutral gas simulations are performed with the EMC3-EIRENE code.},

  doi          = {10.1088/1741-4326/aaaf99},

  journal      = {Nuclear Fusion},

  number       = 5,

  volume       = 58,

  place        = {United States},

  year         = {2018},

  month        = {2}

}

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DOI: 10.1088/1741-4326/aaaf99

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Figures / Tables:

Figure 1: The SAS divertor configuration in DIII-D. Misalignment between the strike point and the divertor slot is approximated by a finite toroidal gap in the divertor baffle at $\varphi$ = 10 . . . 10 deg. A flat continuation of the main divertor plate is applied within the gapmore »

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