Reciprocating probe measurements of L-H transition in LHCD H-mode on EAST EAST

1. Reciprocating probe measurements of L-H transition in LHCD H-mode on EAST EAST Peng Liu Institute of Plasma Physics Chinese Academy of Sciences 1st APTWG meeting June 2011 NIFS Toki

2. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

3. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

4. Motivation • H-modes have rarely been obtained in Lower Hybrid Current Drive (LHCD) alone. • LHCD has produced dithering ELMy H-modes on JET in single null divertor plasmas and ELM-free H-modes on JT-60 in limiter plasmas. • In the recent experimental campaign of EAST the first H-mode was produced by lower-hybrid wave (LHW) as the only auxiliary power source. • Two reciprocating probes were mounted at the outer midplane, toroidally separated by 89°to provide direct measurement of L-H transition in LHCD H-mode.

5. Introduction First H mode on 7 Nov. 2010, 23:16 Shot number 32525 EAST missions : 1MA, 20MW high-performance steady-state operation (SSO). • Stationary H mode operation > 400 s Achieved : 6.4 s H mode, HIPB98(y,2)~0.9 • Long pulse divertor operation >1000 s Achieved : 100 s L mode, Te0~1.2 keV • Plasma current up to 1.5 MA Achieved : Ip = 1 MA, L mode EAST parameters : Major radius : R0 = 1.9 m Minor radius : a = 0.5 m Toroidal field : Bt = 3.5 T Elongation :  = 2 Triangularity :  = 0.65 H mode 100 s 1 MA

6. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

7. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

8. First H-mode on EAST 490 H mode shots in total 89% : POhm + PLHW including the first H mode discharge duration 3.6 s, limited by Ip flat top durations 11% : POhm + PLHW + PICRF duration  6.4 s, limited by discharge durations 51% : DN or unbalanced DN 16% : LSN (BB towards lower X-point) 33% : during configuration switches from DN to LSN 0% : USN 80% : first L-H transition during Ip flat top 16% : first L-H transition during Ip ramp-up 4% : first L-H transition during Ip ramp-down Parameters at L-H : Bt = 1.4~2 T Ip = 0.4~0.8 MA ne = 1.9~3.41019m3 PLHW = 0.5~1.1 MW PICRF < 0.5 MW SA = 38~42 m2  = 1.64~1.94 low = 0.45~0.58 q95 = 2.7~5.0

9. Key actions leading to the H mode • Wall conditioning by lithium coating : to reduce recycling, suppress impurities and radiation. • Outer gap optimization by isoflux control and antenna position adjustment : to improve LHW & ICRF power coupling and minimize impurity generation by the plasma-antenna interaction. • Local gas puffing near the LHW launcher : to improve LHW coupling (not routinely applied). • Shape the plasma into a divertor configuration early during Ip ramp-up : to reduce impurities and radiation. • Increase the gas puffing rate during Ip ramp-up : to suppress runaway electrons. • Gas fueling from either the HFS or the domes : higher fueling efficiency than LFS gas fueling. Typical H-mode discharge on EAST. The ne increased after H-mode started, and returned L-mode because Ploss increased too much.

10. LHW power coupling problem Multiple L-H-L transitions : when the applied LHW power was marginal to the threshold. H-L back transitions : increased power loss by radiation & LHW reflection during ELM-free phases.

11. What triggers the transition?

12. Mean Er in L-H transition

13. There are differences between experiments

14. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

15. Two fast reciprocating probe systems for toroidally long-distance correlation

16. Reciprocating probe measurements of L-H transition in LHCD H-mode on EAST

17. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

18. Comparison of L and H mode 36291 36292 Two adjacent shots, red line for L-mode(36292) and black line for H-mode(36291); the probes were at the same position

19. L-H transition Ploss = Paux+ Poh–Prad–dWp/dt

20. SOL Profiles Time history in SOL SOL profiles Reciprocating Langmuir probe measurements at the outer midplane showed that the ne and Te in the SOL were significantly reduced in the ELM-free phase, resulting in increased LHW reflection.

21. GAM disappear during H mode Reciprocating probe data at the plasma edge show GAM oscillation in L mode but it disappeared in H mode.

22. Negative spike before L-H transition L-mode H-mode The negative spike correspond with Ha

23. Dithering just before L-H transition Dithering Dithering like Dithering like was frequently observed just before L-H transition or sometimes in L mode when ne>2

24. Outline • Introduction • L-H transition measured by RCP • First H-mode on EAST • Experiment setup • L-H transition • Summary

25. Summary • Stationary ELMy H mode has been achieved with only 1 MW of LHCD on EAST. • Reciprocating Langmuir probe measurements at the outer midplane showed that the ne and Te in the SOL were significantly reduced in the ELM-free phase • Multiple L-H-L transitions were observed during a single shot, when the applied LHW power was marginal to the threshold. • Some typical phenomena were observed by reciprocating probe measurement when L-H transition occurred.

26. Thank you very much for your attention!