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EASTEASTRecent Progress on Long Pulse Divertor Operation in EAST
H.Y. Guo, J. Li, G.-N. Luo Z.W. Wu, X. Gao, S. Zhu and the EAST Team
19th PSI ConferenceMay 24–28, 2010, San Diego, CA
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EASTEAST
EAST Superconducting Tokamak
& Recent Upgrade on Plasma Wall Interface
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Divertor Asymmetry & Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
Content of Talk
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EASTEASTContent of Talk
EAST Superconducting Tokamak
& Recent Upgrade on Plasma Wall Interface
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Divertor Asymmetry & Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
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EAST Was Built to Address High Power, Long Pulse Operation Issues for ITER
ITEREAST
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Divertor Configurations: SN & DN
ITEREAST
SNSN DNDN
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Divertor Configurations: SN & DN
D0
Adopted ITER-like vertical target structure with tightly fitted side baffles and a central dome to minimize neutral.
Reduce peak power loading on the divertor target plates, most of the particles incident on the vertical target are re-emitted towards and ionized near the separatrix below the X-point.
Facilitate partial detachment near the strike points: minimize peak power loading, also ensure adequate particle exhaust.
EAST
ITER
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EAST Initial SS First Wall Was Upgraded to Full Graphite Wall w/ Active Cooling
SiC coated, doped graphite GBST1308 (1%B4C, 2.5%Si,
7.5%Ti) tiles are used to cover the divertor panels and vessels.
Graphite tiles are bolted to the water-cooled plates and vessel wall to limit temperature rise at tiles to 900 C at 2 MW/m2.
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A New Internal Divertor Cryopump Was Installed to Provide Active Divertor Pumping
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EASTEASTContent of Talk
EAST Superconducting Tokamak
& Recent PWI Upgrade
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Divertor Asymmetry & Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
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Steady Divertor Discharges Have Been Achieved with Pulse Duration > 60 s
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Steady Divertor Discharges Have Been Achieved with Pulse Duration > 60 s
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Demonstrated Three Distinct Divertor Plasma Regimes with Density Ramp-up
Ion saturation current Is (ion flux) increases with density ne.
Is further increase until roll over.
Particle flux starts to decrease as ne increases.
Conduction-Limited
Detached
Sheath-Limited
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Demonstrated Three Distinct Divertor Plasma Regimes with Density Ramp-up
Ion saturation current Is (ion flux) increases with density ne.
Is further increase until roll over.
Particle flux starts to decrease as ne increases.
Conduction-Limited
Detached
Sheath-Limited
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Radiation Appears to Move toward X-point during Detachment
Dɑ IntensitiesVisible Light
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Achieved Partial Detachment w/ Te < 2 eV Near Sepatratrix, As Expected for V Target
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Active Control of Peak Heat Flux Using Localized Gas Puffing
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EASTEASTContent of Talk
EAST Superconducting Tokamak
& Recent PWI Upgrade
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Divertor Asymmetry & Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
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EASTEASTDivertor Inn-Out Asymmetry for DN
Particle and heat fluxes to the outer target are much higher than inner target.
Strong fluctuations are present in the outer divertor, presumably due to enhanced turbulence on the outboard side with bad curvature, but decreases at higher densities
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Particle fluxes to both divertor targets are higher for SN divertor, presumably due to reduced target surface area.
But, divertor asymmetry is reduced for SN divertor, possibly due to fast parallel transport along SOL via the top.
Fluctuations are significantly reduced at inner target
Comparison between DN and SN
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EASTEASTContent of Talk
EAST Superconducting Tokamak
& Recent PWI Upgrade
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
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Influence of Classical Drifts on Divertor Asymmetry
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//
B
B
q
TTkB
B
vB
2BE
BEv
Affects inner/outer asymmetry
Affects top/down asymmetry
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Effect of BT Reversal – DN Top/Down Asymmetry
Normal BT (clockwise, viewing from top): more fluxes in lower divertor, in the ion B × B Direction.
Reverse BT: Reduce, even reverse top/down asymmetry.
BottomBottom BottomBottom
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Revering BT led to strong particle fluxes on outer divertor target, most likely driven by Er ×BT drift via private region.
This resulted in early detachment in both outer and inner divertors, accompanied by large core radiations seen by SX, ultimately affecting density limit.
Effect of BT Reversal – SN Inner/Outer Asymmetry
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Revering BT led to strong particle fluxes on outer divertor target, most likely driven by Er ×BT drift via private region.
This resulted in early detachment in both outer and inner divertors, accompanied by large core radiations seen by SX, ultimately affecting density limit.
Effect of BT Reversal – SN Inner/Outer Asymmetry
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EASTEASTContent of Talk
EAST Superconducting Tokamak
& Recent PWI Upgrade
Long Pulse Divertor Plasma Behavior
Comparison Between Single Null & Double
Null Divertor Configurations
Effect of BT Reversal
B2/EIRENE Modeling & Implications for High
Power Long Pulse Operation
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Comparison with Initial SOLPS-B2/EIRENE modeling
SN – Normal BT, Ps = 0.25 MW with Pi = Pe, ns = 51018 m-3 ~ ½ <ne>
D = 0.5 m2/s, i = e = 1 m2/s
Carbon: Phys. + Chem @ 0.5eV, w/ Ych = 2%
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Predictions for High Powered Dischargeson EAST w/ Ps ~ 4 MW (D = 0.3 m2/s)
DN exhibits strong in-out divertor asymmetry in target power loading.
SN in-out peak heat fluxes are similar (without taking into account of drifts and turbulence- induced transport).
Detachment and hence significant reduction in peak target head load occurs at much higher separatrix density, ns ~ 1019 m-3.
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EASTEASTSummary & Conclusions
EAST has demonstrated stable, long pulse divertor operation up to ~ 65 s, entirely driven by LHCD, and
Carried out first systematic assessment of divertor performance, e.g., detachment, SN/DN comparison, divertor asymmetry and effect of field reversal etc., in Ohmic and L-mode conditions.
Modeling by SOLPS-B2/EIRENE indicates that additional impurity seeding is needed to control peak target heat load for high power long pulse operation on EAST.
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EASTEASTOther EAST Divertor Presentations
P1-33, Mon-PM: Y.P. Chen, “Modelling Studies of SOL-Divertor Plasmas in EAST Tokamak with High Heating and Current Driving Power”
P2-67, Tue-PM: Q. S. Hu, “Particle Exhaust and Recycling Control by Active Divertor Pumping in EAST”
O-24, Thu-AM: Z.W. Wu, “First Study of EAST Divertor by Impurity Puffing”
P3-11, Thu-PM: W. Gao, “Effect of Localized Gas Puffing on Divertor Plasma Behavior in EAST”