Recent Progress on Long Pulse Divertor Operation in EAST

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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


& Recent Upgrade on Plasma Wall Interface







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EASTEAST

EAST Was Built to Address High Power, Long Pulse Operation Issues for ITER

ITEREAST

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EASTEAST

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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EASTEAST

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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& Recent PWI Upgrade







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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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EASTEAST

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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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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Effect of BT Reversal



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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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EASTEAST

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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EASTEAST

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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Effect of BT Reversal



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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”

Documents

Recent Progress on Long Pulse Divertor Operation in EAST