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Overview of EAST H-mode Plasma

2 nd A3 Foresight Workshop on Spherical Torus, January 6 - 8, Tsinghua University, 2013 Beijing, China. Overview of EAST H-mode Plasma. Liang Wang * , J. Li, B.N. Wan, H.Y. Guo , Y. Liang, G.S. Xu , L.Q. Hu for EAST Team & Collaborators .

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Overview of EAST H-mode Plasma

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  1. 2nd A3 Foresight Workshop on Spherical Torus, January 6 - 8, Tsinghua University, 2013 Beijing, China Overview of EAST H-mode Plasma Liang Wang*, J. Li, B.N. Wan, H.Y. Guo, Y. Liang, G.S. Xu, L.Q. Hu for EAST Team & Collaborators Institute of Plasma Physics, Chinese Academy of Sciences *Email: wliang@ipp.ac.cn

  2. Outline • Introduction • H-mode access & power threshold • ELM characteristics, energy loss and divertor power load • Active control of giant ELMs • Long pulse H-mode over 30 s in EAST • Summary and conclusion 2

  3. Experimental Advanced Superconducting Tokamak • Major radius: R0= 1.9 m • Minus radius: a = 0.5 m • Plasma duration: t=1000 s • Plasma current: Ip=1 MA • Toroidal field: BT=3.5 T • Triangularity: δ= 0.3-0.65 • SN/DN divertor configuration • Commenced operation on 26 Sept. 2006 • First H mode on 7 Nov. 2010 • H-mode duration over 30s on 28 May 2012 • Divertor operation over 400s on 21 June 2012

  4. EAST Upgrade Capacity & Near-term Plan RMP Coils (n=4)

  5. Outline • Introduction • H-mode access & power threshold • ELM characteristics, energy loss and divertor power load • Active control of giant ELMs • Long pulse H-mode over 30 s in EAST • Summary and conclusion 5

  6. Lithium wall conditionings • Reduce recycling • Suppress impurities • Benefit ICRF &LHCD coupling • Mitigate ELMs • Increasing Li Coverage (85% @2012 vs 30% @2010) • Active Li injection to help operate long pulse H-mode • Need one more oven for full surface coating.

  7. H-mode threshold power Threshold power of EAST H modes is aligned with predictions of the international tokamakscaling 2012, dithering LH transition 2010 campaign • Threshold power shows no dependence on heating method • Appears to have a roll-over ne ~ 2.2 1019/m3 • Low density limit for H-mode access B.N. Wan et al., Nucl. Fusion 53, 104006 (2013)

  8. Unfavorable BB facilitates H-mode access in EAST • H-mode access in EAST favors the divertor configuration with ion B×∇B drift away from the X-point, in contrast to other tokamaks. • Thus,LSN with reversed Btfacilitates access to H-modes Type I ELMy H-mode in EAST was only achieved in LSN. Normal Bt, 2012 BB ↓ Reversed Bt, 2010 campaign BB ↑ H.Y. Guo et al., Nucl. Fusion 54, 013002 (2014)

  9. Outline • Introduction • H-mode access & power threshold • ELM characteristics, energy loss and divertor power load • Active control of giant ELMs • Long pulse H-mode over 30 s in EAST • Summary and conclusion 9

  10. Type-I ELMs in EAST Divertor particle fluxes • LSN with LHW+ICRH • Heating power: Pheat~1.5PLH • Good confinement: H98 ~1 • Lower density : ne/nG < 0.5 • Repetition freq.: fELM< 50 Hz • Peak heat flux: ~10 MWm-2 Contours of jsat UI (a), UO (b), LI (c) and LO (d) divertor targets for a typical Type-I ELMy H-mode. L. Wang et al., Nucl. Fusion 53, 073028 (2013)

  11. Type-I ELM power load, pedestal energy loss • Pedestal energy loss: ~ 8.5% • Divertor power load: ~ 5% • Most of Type I ELM ejected power is deposited on the outboard divertor ELM energy loss and divertor heat load for two groups of coherent type-I ELMs in #41200 & #42556 Characteristics of divertor power load and peak heat flux for a Type I ELM.

  12. Compound ELMs in EAST • Characteristic: an initial ELM spike followed by a number of small ELMs. • Achieved in DN (δ=0.46) with LHW+ICRH, Pheat~1.3MW • Good confinement: H98 ~1 • Density: ne/nG>0.5 • ELM frequency: fELM ~50Hz • The plasma energy loss & div. power load: both ~ 4.5% . • Peak heat flux : between that of type-I and type-III ELMs.

  13. Essential difference between compound ELMs &ELM filaments: different time scale • The time scale of a compound ELM: a few ms • The interval time betw. adjacent ELM filaments: 150-250μs X.Q. Xu et al 24th IAEA FEC Type-III ELM filaments observed by divertor LPs (left) and visible camera w/ BOUT++ (right).

  14. Type-III ELMs in EAST • The most common ELMs observed in EAST up to now. • Achieved USN, DN, LSN  • Pheat~PLH: LHW only, ICRF only, LHW+ICRF • fELM=0.2-0.8kHz • ne/nG= 0.2-0.65 • Confinement: H98 = 0.5-0.8 • No ∆Wdia was observed • ∆Wdiv/Wdia : 1-2%. • Peak heat flux: ~2MW/m2. G. S. Xu et al., NF 51, 072001 (2011); L. Wang et al., NF 52, 063024 (2012)

  15. Scaling of divertor power footprint width in RF-heated type-III ELMy H-mode • Three diagnostics (Divertor LPs +IR camera +LFS Reciprocating LPs) independently demonstrated . • In addition, the systematic experiments of EAST shows the inverse scaling is independent div-configuration (LSN, DN, USN). L. Wang et al., submitted to Nucl. Fusion, December 2013

  16. Very small ELMs in EAST (type-II like) • Achieved with LHW+ICRH, Pheat~1.7MW, q95 ≥ 4.5 • H98= 0.8-0.9, between type-I and type-III ELM regimes • High δ: very small ELMs  type-I ELMs when δ was reduced to ~ 0.4. • High density: ne/nG = 0.5 - 0.6 • High freq: fELM = 0.8-1.5kHz • Peak heat flux: < 1MWm-2 largely • No ∆Wdia was observed • Broadband MHD mode: 20-50kHz L. Wang et al., Nucl. Fusion 53, 073028 (2013)

  17. Outline • Introduction • H-mode access & power threshold • ELM characteristics, energy loss and divertor power load • Active control of giant ELMs • Long pulse H-mode over 30 s in EAST • Summary and conclusion 17

  18. Demonstrated for the 1st time Edge magnetic topology change by LHCD Helical Radiation Belts (helical current sheets) induced by LHCD Y. Liang, …, L. Wang et al., PRL 110, 235002 (2013)

  19. Strong mitigation of ELMs with LHCD • ICRF-dominated + 10Hz LHW modulation (LHW-off: 50ms ~ ½τE) • H98=0.8; Wdia|LH: 50 100kJ • LHW off: fELM ~150Hz • LHW on: ELMs disappear or sporadically appear w/ fELM~600Hz • Peak particle flux: ↓by 2-4 • Wdiavaried slightly: within ±5% • A quick reduction of Гi,divduring inter-ELM can be seen when LHW was switched off. Y. Liang, …, L. Wang et al., PRL 110, 235002 (2013)

  20. Demonstrated for the 1st time ELM Pacing by Innovative Li-granule Injection Collaborated with PPPL Li • Triggering ELMs (~25 Hz) with 0.7 mm Li granules @ ~45 m/s. • ELM trigger efficiency after L-H transition: ~100%. • Much lower divertor particle/heat loads than intrinsic type-I ELMs. D. Mansfield et al., Nucl. Fusion 53, 113023 (2013)

  21. ELM control by SMBI • SMBI: Supersonic Molecular Beam Injection, Initially developed by SWIP.CN, successfully applied on HL-2A, KSTAR & EAST X. L. Zou et al., 24th IAEA FEC, San Diego

  22. SHF can be actively controlled with SMBI • Striated Heat Flux (SHF ) region in the far-SOL can be actively controlled with SMBI. • Characteristic of LHCD heating scheme • SMBI significantly enhancingSHF, while reducing peak heat fluxes near strike point. • Achieving similar results with conventional gas puff or Ar seeding.

  23. SHF can be actively controlled by regulating edge particle fluxes • For SHF: qSHF~ ΓiTped, Tped~ 350 eVqSHFincreaseswithΓi. • At OST: qOST~ ΓiTdiv, Tdiv~ Γi-1, qOSTremainssimilar. • A unique physics feature of ergodized plasma edge by LHCD. • Allowing control of the ratio of qSHF/qOST, thus divertor power deposition area via control of divertor plasma conditions. J. Li, …, L. Wang et al., Nature Phys. 9, 817 (2013) L. Wang et al., submitted to PSI - 2014, invited talk

  24. Achieved long pulse H-mode over 30s w/ small ELMs to minimize transient heat load • Predominantly small ELMs with H98 ~ 0.9, between type-I and type-III ELMyH-modes. • Target heat flux is largely below 2 MW/m2. • Accompanied by QCM, continuously removing heat and particles. J. Li, … , L. Wang et al., Nature Physics 9, 817 (2013)

  25. Outline • Introduction • H-mode access & power threshold • ELM characteristics, energy loss and divertor power load • Active control of giant ELMs • Long pulse H-mode over 30 s in EAST • Summary and conclusion 25

  26. Summary & Conclusion • Significant progress has been made on H-mode & ELMs toward long pulse operations in EAST on both technol. & phys. fronts. • Various ELM dynamics and their behaviors have been characterized. • LHCD leads to edge plasma ergodization, mitigating ELM transient heat load and broadening the divertor footprint. LHCD + SMBI allows control of SS target heat flux distribution by regulating divertor conditions. • H-mode access in EAST favors the divertor configuration with ion B×B drift away from the X-point, in contrast to other tokamaks. • Achieved repeatable, long-pulse H-mode over 30 s successfully. • EAST is being upgraded with ITER-like W mono-block divertor and more than 20 MW CW H&CD, offering an exciting opportunity and great challenge for H-mode studies.

  27. Thank you! Welcome to join EAST experiments! We will be right here waiting for you … EAST – Test Bed for ITER

  28. Back up

  29. LFS & HFS wall: Graphite  Molybdenum • Mo first wall • Water-cooled • Cryo-pump 2012: Mo + graphite div. 2010: full graphite

  30. Type-III ELMs in EAST • The most common ELMs observed in EAST up to now. • Achieved in DN, LSN, USN • LHW only, ICRF only, LHW+ICRH, Pheat~PLH • Frequency: fELM=0.2-0.8kHz • Density: ne/nG= 0.2-0.65 • Confinement: H98 =0.5-0.8 • No ∆Wdia was observed • Divertor power load: 1-2%. • Peak heat flux: ~2MW/m2.

  31. The very small ELMs are type-II like • Operation space of Type II ELMs: high δ, high κ, high ne , and high q95 • Confinement of Type II ELMs: H98 being 10% less than Type I ELMs • Unique feature of Type II ELMs: w/ broadband MHD mode • ( 30±10kHz@ASDEX-Upgrade; 10-40kHz@JET) Time-frequency spectrum of Mirnov magnetic signal.

  32. Flexible boundary control with LHCD • The long pulse H-mode was achieved with dominant LHCD, with additional ICRH. • LHCD induces drives n=1 helical currents at edge, leading to 3D distortion of magnetic topology, similar to RMP • LHCD appears to be effective at controlling ELMs over a broad range q95, in contrast to fixed RMP coils.

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