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Global calculation of neoclassical impurity transport including the variation of electrostatic potential

Part of: Focus on Fusion

Published online by Cambridge University Press:  25 June 2020

Keiji Fujita Open the ORCID record for Keiji Fujita [Opens in a new window] ,
S. Satake ,
R. Kanno ,
M. Nunami ,
M. Nakata ,
J. M. García-Regaña ,
J. L. Velasco  and
I. Calvo
Keiji Fujita*
Affiliation:
The Graduate University for Advanced Studies (SOKENDAI), 322-6Oroshi-cho, Toki, Japan
S. Satake
Affiliation:
The Graduate University for Advanced Studies (SOKENDAI), 322-6Oroshi-cho, Toki, Japan National Institute for Fusion Science, 322-6Oroshi-cho, Toki, Japan
R. Kanno
Affiliation:
The Graduate University for Advanced Studies (SOKENDAI), 322-6Oroshi-cho, Toki, Japan National Institute for Fusion Science, 322-6Oroshi-cho, Toki, Japan
M. Nunami
Affiliation:
The Graduate University for Advanced Studies (SOKENDAI), 322-6Oroshi-cho, Toki, Japan National Institute for Fusion Science, 322-6Oroshi-cho, Toki, Japan
M. Nakata
Affiliation:
The Graduate University for Advanced Studies (SOKENDAI), 322-6Oroshi-cho, Toki, Japan National Institute for Fusion Science, 322-6Oroshi-cho, Toki, Japan
J. M. García-Regaña
Affiliation:
Laboratorio Nacional de Fusión, CIEMAT, Avenida Complutense, 40, 28040, Madrid, Spain
J. L. Velasco
Affiliation:
Laboratorio Nacional de Fusión, CIEMAT, Avenida Complutense, 40, 28040, Madrid, Spain
I. Calvo
Affiliation:
Laboratorio Nacional de Fusión, CIEMAT, Avenida Complutense, 40, 28040, Madrid, Spain
*
†Email address for correspondence: fujita.keiji@nifs.ac.jp
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Abstract

Recently, the validity range of the approximations commonly used in neoclassical calculation has been reconsidered. One of the primary motivations behind this trend is observation of an impurity hole in LHD (Large Helical Device), i.e. the formation of an extremely hollow density profile of an impurity ion species, such as carbon $\text{C}^{6+}$, in the plasma core region where a negative radial electric field ($E_{r}$) is expected to exist. Recent studies have shown that the variation of electrostatic potential on the flux surface, $\unicode[STIX]{x1D6F7}_{1}$, has significant impact on neoclassical impurity transport. Nevertheless, the effect of $\unicode[STIX]{x1D6F7}_{1}$ has been studied with radially local codes and the necessity of global calculation has been suggested. Thus, we have extended a global neoclassical code, FORTEC-3D, to simulate impurity transport in an impurity hole plasma including $\unicode[STIX]{x1D6F7}_{1}$ globally. Independently of the $\unicode[STIX]{x1D6F7}_{1}$ effect, an electron root of the ambipolar condition for the impurity hole plasma has been found by global simulation. Hence, we have considered two different cases, each with a positive (global) and a negative (local) solution of the ambipolar condition, respectively. Our result provides another support that $\unicode[STIX]{x1D6F7}_{1}$ has non-negligible impact on impurity transport. However, for the ion-root case, the radial $\text{C}^{6+}$ flux is driven further inwardly by $\unicode[STIX]{x1D6F7}_{1}$. For the electron-root case, on the other hand, the radial particle $\text{C}^{6+}$ flux is outwardly enhanced by $\unicode[STIX]{x1D6F7}_{1}$. These results indicate that how $\unicode[STIX]{x1D6F7}_{1}$ affects the radial particle transport crucially depends on the profile of the ambipolar-$E_{r}$, which is found to be susceptible to $\unicode[STIX]{x1D6F7}_{1}$ itself and the global effects.

Keywords

fusion plasmaplasma confinementplasma simulation
Type
Research Article
Information
Journal of Plasma Physics , Volume 86 , Issue 3 , June 2020 , 905860319
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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