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Title: Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport

Abstract

Flux-surface variations of the electrostatic potential are typically neglected in standard neoclassical theory, but in 3D devices they can be large enough to affect the radial particle flux of impurities. The radially local drift-kinetic equation solver SFINCS (stellarator Fokker–Planck iterative neoclassical conservative solver) (Landreman et al 2014 Phys. Plasmas 21 042503) has been updated to account for these variations. In the present work we use SFINCS to perform a novel study of neoclassical particle transport in stellarators, where we simultaneously account for the flux-surface potential variations, several kinetic species including non-adiabatic electrons and non-trace impurities, and the full linearized Fokker–Planck–Landau collision operator for self- and inter-species collisions (with no expansion made in mass ratio). We also make a self-consistent calculation of the ambipolar radial electric field, to analyze how it is affected by the flux-surface variations and the presence of non-trace impurities. In a simulated Wendelstein 7-X plasma, we find that the impact of the flux-surface variations on the radial particle fluxes of all plasma species is small. In contrast, for an experimental impurity hole discharge in the Large Helical Device (LHD) the carbon flux can be strongly modified by the flux-surface potential variation and also the calculated ambipolar radialmore » electric field can change. Nonetheless, around mid radius the potential variations cause enhanced inward neoclassical carbon fluxes, rather than causing outward fluxes, thus suggesting that the role of flux-surface potential variations in neoclassical transport may not be the explanation for the impurity hole phenomenon observed in LHD plasmas.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [3];  [4]
  1. Max-Planck-Institut für Plasmaphysik, Greifwald (Germany)
  2. Univ. of Maryland, College Park, MD (United States)
  3. Laboratorio Nacional de Fusión (LNF), Madrid (Spain)
  4. National Inst. for Fusion Science, Toki (Japan)
Publication Date:
Research Org.:
Univ. of Maryland, College Park, MD (United States); Univ. of California, Berkeley, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1499870
Grant/Contract Number:  
FG02-93ER54197; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 8; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Mollén, A., Landreman, M., Smith, H. M., García-Regaña, J. M., and Nunami, M. Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport. United States: N. p., 2018. Web. https://doi.org/10.1088/1361-6587/aac700.
Mollén, A., Landreman, M., Smith, H. M., García-Regaña, J. M., & Nunami, M. Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport. United States. https://doi.org/10.1088/1361-6587/aac700
Mollén, A., Landreman, M., Smith, H. M., García-Regaña, J. M., and Nunami, M. Mon . "Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport". United States. https://doi.org/10.1088/1361-6587/aac700. https://www.osti.gov/servlets/purl/1499870.
@article{osti_1499870,
title = {Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport},
author = {Mollén, A. and Landreman, M. and Smith, H. M. and García-Regaña, J. M. and Nunami, M.},
abstractNote = {Flux-surface variations of the electrostatic potential are typically neglected in standard neoclassical theory, but in 3D devices they can be large enough to affect the radial particle flux of impurities. The radially local drift-kinetic equation solver SFINCS (stellarator Fokker–Planck iterative neoclassical conservative solver) (Landreman et al 2014 Phys. Plasmas 21 042503) has been updated to account for these variations. In the present work we use SFINCS to perform a novel study of neoclassical particle transport in stellarators, where we simultaneously account for the flux-surface potential variations, several kinetic species including non-adiabatic electrons and non-trace impurities, and the full linearized Fokker–Planck–Landau collision operator for self- and inter-species collisions (with no expansion made in mass ratio). We also make a self-consistent calculation of the ambipolar radial electric field, to analyze how it is affected by the flux-surface variations and the presence of non-trace impurities. In a simulated Wendelstein 7-X plasma, we find that the impact of the flux-surface variations on the radial particle fluxes of all plasma species is small. In contrast, for an experimental impurity hole discharge in the Large Helical Device (LHD) the carbon flux can be strongly modified by the flux-surface potential variation and also the calculated ambipolar radial electric field can change. Nonetheless, around mid radius the potential variations cause enhanced inward neoclassical carbon fluxes, rather than causing outward fluxes, thus suggesting that the role of flux-surface potential variations in neoclassical transport may not be the explanation for the impurity hole phenomenon observed in LHD plasmas.},
doi = {10.1088/1361-6587/aac700},
journal = {Plasma Physics and Controlled Fusion},
number = 8,
volume = 60,
place = {United States},
year = {2018},
month = {6}
}

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    Works referencing / citing this record:

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    • García-Regaña, J. M.; Estrada, T.; Calvo, I.
    • Plasma Physics and Controlled Fusion, Vol. 60, Issue 10
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    Impact of main ion pressure anisotropy on stellarator impurity transport
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    Collisional transport of impurities with flux-surface varying density in stellarators
    journal, August 2018


    The importance of the classical channel in the impurity transport of optimized stellarators
    journal, July 2019