1 EAST Recent 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 19 th PSI Conference May 24–28, 2010, San Diego, CA

2 EAST 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 B T Reversal B2/EIRENE Modeling & Implications for High Power Long Pulse Operation Content of Talk

3 EAST 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 B T Reversal B2/EIRENE Modeling & Implications for High Power Long Pulse Operation

4 EAST EAST Was Built to Address High Power, Long Pulse Operation Issues for ITER ITER  t = 1000 s  R = 1.9 m, a = 0.5 m  I p = 1 MA  B T = 3.5 T  t = 400 s  R = 6.2 m, a = 2 m  I p = 15 MA  B T = 5.3 T

5 EAST Divertor Configurations: SN & DN ITER EASTSNDN EAST has flexible poloidal field control system, allowing both single null and double null divertor configurations.

6 EAST Divertor Configurations: SN & DN D0D0  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

7 EAST EAST Initial SS First Wall Was Upgraded to Full Graphite Wall w/ Active Cooling  SiC coated, doped graphite GBST1308 (1%B 4 C, 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/m 2. SiC coating reduces erosion near strike points by suppressing chemical sputtering; also reduces C redeposition elsewhere by enhancing C reflection (Qian Xu, Thu PM, P3-69)

8 EAST A New Internal Divertor Cryopump Was Installed to Provide Active Divertor Pumping Pumping speed: 75 m 3 /s for D 2 75 m 3 /s for D m 3 /s for H m 3 /s for H 2

9 EAST Content 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 B T Reversal B2/EIRENE Modeling & Implications for High Power Long Pulse Operation

10 EAST Steady Divertor Discharges Have Been Achieved with Pulse Duration > 60 s

11 EAST Steady Divertor Discharges Have Been Achieved with Pulse Duration > 60 s

12 EAST Demonstrated Three Distinct Divertor Plasma Regimes with Density Ramp-up  Ion saturation current I s (ion flux) increases with density n e.  I s further increase until roll over.  Particle flux starts to decrease as ne increases. Conduction-Limited Detached Sheath-Limited Plasma detachment reduces peak particle & heat fluxes, as well as associated material damage, essential for steady-state operations.

13 EAST Demonstrated Three Distinct Divertor Plasma Regimes with Density Ramp-up  Ion saturation current I s (ion flux) increases with density n e.  I s further increase until roll over.  Particle flux starts to decrease as ne increases. Conduction-Limited Detached Sheath-Limited Plasma detachment reduces peak particle & heat fluxes, as well as associated material damage, essential for steady-state operations.

14 EAST Radiation Appears to Move toward X-point during Detachment D ɑ Intensities Visible Light

15 EAST Achieved Partial Detachment w/ Te < 2 eV Near Sepatratrix, As Expected for V Target Detachment occurs near separatrix, with far SOL still attached to reduce peak heat flux and ensure adequate pumping T e < 2 eV at detachment

16 EAST Active Control of Peak Heat Flux Using Localized Gas Puffing Reduce particle and heat fluxes near outer strike point with D 2 gas puffing from outer divertor

17 EAST Content 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 B T Reversal B2/EIRENE Modeling & Implications for High Power Long Pulse Operation

18 EAST Divertor 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

19 EAST  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

20 EAST Content of Talk EAST Superconducting Tokamak & Recent PWI Upgrade Long Pulse Divertor Plasma Behavior Comparison Between Single Null & Double Null Divertor Configurations Effect of B T Reversal B2/EIRENE Modeling & Implications for High Power Long Pulse Operation

21 EAST Influence of Classical Drifts on Divertor Asymmetry Affects inner/outer asymmetry Affects top/down asymmetry Reversing toroidal field direction affects both drifts.

22 EAST Effect of B T Reversal – DN Top/Down Asymmetry  Normal B T (clockwise, viewing from top): more fluxes in lower divertor, in the ion B ×  B Direction.  Reverse B T : Reduce, even reverse top/down asymmetry. BottomBottom

23 EAST  Revering B T led to strong particle fluxes on outer divertor target, most likely driven by E r ×B T 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 B T Reversal – SN Inner/Outer Asymmetry Reversed BT for SN operations led to early divertor detachment and stronger core radiation, reducing Ohmic density limit.

24 EAST  Revering B T led to strong particle fluxes on outer divertor target, most likely driven by E r ×B T 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 B T Reversal – SN Inner/Outer Asymmetry Reversed BT for SN operations led to early divertor detachment and stronger core radiation, reducing Ohmic density limit.

25 EAST Content 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

26 EAST Comparison with Initial SOLPS- B2/EIRENE modeling  SN – Normal B T, P s = 0.25 MW with P i = P e, n s = 5  m -3 ~ ½  D  = 0.5 m 2 /s,  i =  e = 1 m 2 /s  Carbon: Phys eV, w/ Y ch = 2% Density decays much slower in outboard SOL, possibly arising form enhanced radial transport by turbulence

27 EAST Predictions for High Powered Discharges on EAST w/ P s ~ 4 MW (D  = 0.3 m 2 /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, n s ~ m -3. EAST SS power handling capacity is presently limited to 2 MW/m 2  additional impurity seeding is needed to promote detachment at lower density, n s ~ m -3, for good confinement & LHCD efficiency

28 EAST Summary & 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.

29 EAST Other 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”