Experimental verification of X-point potential well formation in unfavorable magnetic field direction

the TCV Team; EUROFusion MST Team

doi:10.1016/j.nme.2020.100839

Experimental verification of X-point potential well formation in unfavorable magnetic field direction

the TCV Team
, EUROFusion MST Team

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

Recent TCV experiments confirm the predicted formation of an electric potential well, below the magnetic X-point, in configurations with unfavorable B_t field direction (ion ∇B drift away from the divertor), that substantially reshapes the typical divertor E×B flow pattern. The local charge balance ∇⋅j in the private flux region (PFR) of diverted tokamak plasmas has been previously argued to be dominated by parallel and diamagnetic currents. This hypothesis is tested herein in TCV discharges by comparison with SOLPS-ITER simulations, fully accounting for drifts and currents. Simulated parallel currents correctly capture measured current profile characteristics for both targets and both B_t-directions, whereas those omitting drifts fail. It is shown that the resulting parallel currents dictate the electric fields in the PFR for low temperature (detached divertor) conditions resulting in locally negative electric plasma potential in configurations with unfavorable H-mode access.

Original language	English
Article number	100839
Journal	Nuclear Materials and Energy
Volume	25
DOIs	https://doi.org/10.1016/j.nme.2020.100839
State	Published - Dec 2020
Externally published	Yes

Funding

This work was carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053 . The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work was supported in part by the Swiss National Science Foundation . This work was supported in part by the US Department of Energy under Award Number DE-SC0010529 .

Keywords

Divertor
Drift effects
Electric potential
Tokamak

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10.1016/j.nme.2020.100839

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title = "Experimental verification of X-point potential well formation in unfavorable magnetic field direction",

abstract = "Recent TCV experiments confirm the predicted formation of an electric potential well, below the magnetic X-point, in configurations with unfavorable Bt field direction (ion ∇B drift away from the divertor), that substantially reshapes the typical divertor E×B flow pattern. The local charge balance ∇⋅j in the private flux region (PFR) of diverted tokamak plasmas has been previously argued to be dominated by parallel and diamagnetic currents. This hypothesis is tested herein in TCV discharges by comparison with SOLPS-ITER simulations, fully accounting for drifts and currents. Simulated parallel currents correctly capture measured current profile characteristics for both targets and both Bt-directions, whereas those omitting drifts fail. It is shown that the resulting parallel currents dictate the electric fields in the PFR for low temperature (detached divertor) conditions resulting in locally negative electric plasma potential in configurations with unfavorable H-mode access.",

keywords = "Divertor, Drift effects, Electric potential, Tokamak",

author = "\{the TCV Team\} and \{EUROFusion MST Team\} and M. Wensing and \{de Oliveira\}, H. and J. Loizu and C. Colandrea and O. F{\'e}vrier and S. Gorno and H. Reimerdes and C. Theiler and A. Smolders and Duval, \{B. P.\} and Tsui, \{C. K.\} and M. Wischmeier and D. Brida and S. Henderson and M. Komm",

note = "Publisher Copyright: {\textcopyright} 2020 The Authors",

year = "2020",

month = dec,

doi = "10.1016/j.nme.2020.100839",

language = "English",

volume = "25",

journal = "Nuclear Materials and Energy",

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T1 - Experimental verification of X-point potential well formation in unfavorable magnetic field direction

AU - the TCV Team

AU - EUROFusion MST Team

AU - Wensing, M.

AU - de Oliveira, H.

AU - Loizu, J.

AU - Colandrea, C.

AU - Février, O.

AU - Gorno, S.

AU - Reimerdes, H.

AU - Theiler, C.

AU - Smolders, A.

AU - Duval, B. P.

AU - Tsui, C. K.

AU - Wischmeier, M.

AU - Brida, D.

AU - Henderson, S.

AU - Komm, M.

PY - 2020/12

Y1 - 2020/12

N2 - Recent TCV experiments confirm the predicted formation of an electric potential well, below the magnetic X-point, in configurations with unfavorable Bt field direction (ion ∇B drift away from the divertor), that substantially reshapes the typical divertor E×B flow pattern. The local charge balance ∇⋅j in the private flux region (PFR) of diverted tokamak plasmas has been previously argued to be dominated by parallel and diamagnetic currents. This hypothesis is tested herein in TCV discharges by comparison with SOLPS-ITER simulations, fully accounting for drifts and currents. Simulated parallel currents correctly capture measured current profile characteristics for both targets and both Bt-directions, whereas those omitting drifts fail. It is shown that the resulting parallel currents dictate the electric fields in the PFR for low temperature (detached divertor) conditions resulting in locally negative electric plasma potential in configurations with unfavorable H-mode access.

AB - Recent TCV experiments confirm the predicted formation of an electric potential well, below the magnetic X-point, in configurations with unfavorable Bt field direction (ion ∇B drift away from the divertor), that substantially reshapes the typical divertor E×B flow pattern. The local charge balance ∇⋅j in the private flux region (PFR) of diverted tokamak plasmas has been previously argued to be dominated by parallel and diamagnetic currents. This hypothesis is tested herein in TCV discharges by comparison with SOLPS-ITER simulations, fully accounting for drifts and currents. Simulated parallel currents correctly capture measured current profile characteristics for both targets and both Bt-directions, whereas those omitting drifts fail. It is shown that the resulting parallel currents dictate the electric fields in the PFR for low temperature (detached divertor) conditions resulting in locally negative electric plasma potential in configurations with unfavorable H-mode access.

KW - Divertor

KW - Drift effects

KW - Electric potential

KW - Tokamak

UR - https://www.scopus.com/pages/publications/85097343041

U2 - 10.1016/j.nme.2020.100839

DO - 10.1016/j.nme.2020.100839

M3 - Article

AN - SCOPUS:85097343041

SN - 2352-1791

VL - 25

JO - Nuclear Materials and Energy

JF - Nuclear Materials and Energy

M1 - 100839

ER -

Experimental verification of X-point potential well formation in unfavorable magnetic field direction

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Keywords

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