TY - JOUR
T1 - Advanced divertor configurations with large flux expansion
AU - Soukhanovskii, V. A.
AU - Bell, R. E.
AU - Diallo, A.
AU - Gerhardt, S.
AU - Kaye, S.
AU - Kolemen, E.
AU - LeBlanc, B. P.
AU - McLean, A.
AU - Menard, J. E.
AU - Paul, S. F.
AU - Podesta, M.
AU - Raman, R.
AU - Ryutov, D. D.
AU - Scotti, F.
AU - Kaita, R.
AU - Maingi, R.
AU - Mueller, D. M.
AU - Roquemore, A. L.
AU - Reimerdes, H.
AU - Canal, G. P.
AU - Labit, B.
AU - Vijvers, W.
AU - Coda, S.
AU - Duval, B. P.
AU - Morgan, T.
AU - Zielinski, J.
AU - De Temmerman, G.
AU - Tal, B.
N1 - Funding Information:
We thank the entire NSTX and TCV Teams for technical, engineering and computer support as well as plasma and diagnostic operations. This work was performed in part under the auspices of the U.S. Department of Energy under Contracts DE-AC52-07NA27344, DE-AC02-09CH11466, DE-AC05-00OR22725, W-7405-ENG-36, DE-FG02-04ER54758 and the Swiss National Science Foundation.
PY - 2013
Y1 - 2013
N2 - 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/m2 to 0.5-1 MW/m2 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 (×2-3) 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 snow-flake 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.
AB - 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/m2 to 0.5-1 MW/m2 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 (×2-3) 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 snow-flake 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.
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U2 - 10.1016/j.jnucmat.2013.01.015
DO - 10.1016/j.jnucmat.2013.01.015
M3 - Article
AN - SCOPUS:84885486008
SN - 0022-3115
VL - 438
SP - S96-S101
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
IS - SUPPL
ER -