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Characteristics of edge localized modes in the superconducting tokamak EAST

Characteristics of edge localized modes in the superconducting tokamak EAST. M. Jiang Institute of Plasma Physics Chinese Academy of Sciences The 1 st APTWG meeting, June 2011, NIFS, Japan. Outline. H-mode access on EAST ELMs behavior ELMs crash Classifications of ELMs

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Characteristics of edge localized modes in the superconducting tokamak EAST

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  1. Characteristics of edge localized modes in the superconducting tokamakEAST M. Jiang Institute of Plasma Physics Chinese Academy of Sciences The 1st APTWG meeting, June 2011, NIFS, Japan

  2. Outline • H-mode access on EAST • ELMs behavior • ELMs crash • Classifications of ELMs • The effects in divertor plasmas • Statistical analysis of ELMs frequency • Control of ELMs by argon puffing • Summary

  3. Outline • H-mode access on EAST • ELMs behavior • ELMs crash • Classifications of ELMs • The effects in divertor plasmas • Statistical analysis of ELMs frequency • Control of ELMs by argon puffing • Summary

  4. H-mode access on EAST • 490 H-mode shots so far • Configurations: DN or • unbalanced DN, LSN • First L-H transition during • Ip flat top, ramp-up and ramp- • down 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

  5. H-mode access on EAST EAST shot 36577 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

  6. Outline • H-mode access on EAST • ELMs behavior • ELMs crash • Classifications of ELMs • The effects in divertor plasmas • Statistical analysis of ELMs frequency • Control of ELMs by argon puffing • Summary

  7. ELM and Pedestal structure EAST shot 34377 reaches MHD instability transport increase pedestal expels particles drops significantly and finally “avalanche model ” ELMs crash The formation of pedestal was confirmed by a sharp rise in XUV at plasma edge. During ELMs, pressure gradient reduced. Between ELMs, it steepens, but is far from the steepness of the ELM-free period

  8. Classifications of ELMs in EAST 1. Type III Most of ELMs on EAST are type III. They usually appeared at heating powers close to the threshold power. A coherent magnetic precursor oscillation was observed on magnetic and electrostatic probes. The frequency of ELMs precursor decreases from 130kHz to 60kHz within 0.4ms. EAST shot 35353 D[a.u.] Mirnov Time [s]

  9. Classifications of ELMs on EAST 2. Type I like • H mode was sustained by 0.3 MW as a result of the hysteresis effect. • Energy loss > 5% • deposited energy on divertor plates >3kJ • The heat load pulses on the outer target plates increase significantly and reach a peak heat load of 4MW/m2.

  10. Classifications of ELMs on EAST 3. Compound ELM EAST shot 33473 D[a.u.] Mirnov Time [s] An initial MHD instability followed by a transient L-phase

  11. Classifications of ELMs on EAST 4. Negative D spikes near X-point High density Inner target X-point Ionization region Not detached at the inner target 14

  12. Classifications of ELMs on EAST 5. quasi-periodic oscillations 6. No evident L-H transition EAST shot 33039 EAST shot 33394 Time [s] Time [s] Before L-H, quasi-periodic oscillation exists. It occurred in almost all H-mode discharge shots

  13. Classifications of ELMs on EAST 7. Strange ELM 8. Mossy ELM EAST shot 33579 EAST shot 33049 Strange ELMs occurred at large current Small ELMs, so called “mossy ELM”

  14. ELM average heat load ~ 2MW/m2 IR CCD camera, 20 ms time resolution Type III ELMs

  15. In-out asymmetry in target heat load Type III ELMs LSN, dRsep = 1 cm Inner > Outer Type III ELMs DN, dRsep = 0 cm Outer > Inner LSN DN IR CCD data IR CCD data

  16. Energy loss by ELM W/W = 1~2% Target probes LSN & DN

  17. Statistical analysis for frequencies q95 indicates the current profile, which dominates kink mode. Kink mode and ballooning mode drive ELM. q95 , the current density and pressure gradient will be in the peeling-ballooning mode stable region.

  18. ELM control by Argon seeding • Argon gas injected from lower outer target at a speed of 41020 particles/s • ELM frequency rises • ELM amplitude decreases • Prad didn’t increase • Ploss increased • Wdia decreased • Effective for shielding impurity

  19. Outline • H-mode access on EAST • ELMs behavior • ELMs crash • Classifications of ELMs • The effects in divertor plasmas • Statistical analysis of ELMs frequency • Control of ELMs by argon puffing • Summary

  20. Summary • Type III ELMy H-mode has been obtained with low LHW power and lithium evaporation and real-time Li powder injection in EAST. • Different kinds of ELMs have been observed in EAST with heating of LHW • ELMs frequency is in the range of several hundred Hz, and decreases with q95 • ELMs behavior can be controlled by puffing gas

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