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conference paper

Advanced divertor configurations with large flux expansion

Soukhanovskii, V. A.
•
Bell, R. E.
•
Diallo, A.
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2013
Journal Of Nuclear Materials
20th International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI)

Experimental studies of the novel snowflake divertor concept (D. Ryutov, Phys. Plasmas 14 (2007) 064502) performed in the NSTX and TCV tokamaks are reviewed in this paper. The snowflake divertor enables power sharing between divertor strike points, as well as the divertor plasma-wetted area, effective connection length and divertor volumetric power loss to increase beyond those in the standard divertor, potentially reducing heat flux and plasma temperature at the target. It also enables higher magnetic shear inside the separatrix, potentially affecting pedestal MHD stability. Experimental results from NSTX and TCV confirm the predicted properties of the snowflake divertor. In the NSTX, a large spherical tokamak with a compact divertor and lithium-coated graphite plasma-facing components (PFCs), the snowflake divertor operation led to reduced core and pedestal impurity concentration, as well as reappearance of Type I ELMs that were suppressed in standard divertor H-mode discharges. In the divertor, an otherwise inaccessible partial detachment of the outer strike point with an up to 50% increase in divertor radiation and a peak divertor heat flux reduction from 3-7 MW/m(2) to 0.5-1 MW/m(2) was achieved. Impulsive heat fluxes due to Type-I ELMs were significantly dissipated in the high magnetic flux expansion region. In the TCV, a medium-size tokamak with graphite PFCs, several advantageous snowflake divertor features (cf. the standard divertor) have been demonstrated: an unchanged L-H power threshold, enhanced stability of the peeling-ballooning modes in the pedestal region (and generally an extended second stability region), as well as an H-mode pedestal regime with reduced (x2-3) Type I ELM frequency and slightly increased (20-30%) normalized ELM energy, resulting in a favorable average energy loss comparison to the standard divertor. In the divertor, ELM power partitioning between snowflake divertor strike points was demonstrated. The NSTX and TCV experiments are providing support for the snowflake divertor as a viable solution for the outstanding tokamak plasma-material interface issues. (C) 2013 Elsevier B.V. All rights reserved.

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Type
conference paper
DOI
10.1016/j.jnucmat.2013.01.015
Web of Science ID

WOS:000330795300015

Author(s)
Soukhanovskii, V. A.
Bell, R. E.
Diallo, A.
Gerhardt, S.
Kaye, S.
Kolemen, E.
Leblanc, B. P.
Mclean, A.
Menard, J. E.
Paul, S. F.
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Date Issued

2013

Publisher

Elsevier Science Bv

Publisher place

Amsterdam

Published in
Journal Of Nuclear Materials
Total of pages

6

Volume

438

Start page

S96

End page

S101

Subjects

snowflake divertor

•

TCV

•

plasma

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
CRPP  
SPC  
Event name
20th International Conference on Plasma-Surface Interactions in Controlled Fusion Devices (PSI)
Available on Infoscience
June 2, 2014
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/103940
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