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Influence of the Dynamic Ergodic Divertor on TEXTOR Discharges

Influence of the Dynamic Ergodic Divertor on TEXTOR Discharges. K.H. Finken, Y. Xu, S.S. Abdullaev, M. Jakubowski, M. Lehnen, M. F. M. de Bock, S. Bozhenkov, S. Brezinsek, C. Busch, I.G.J. Classen, J.W. Coenen, D. Harting, M. von Hellermann,

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Influence of the Dynamic Ergodic Divertor on TEXTOR Discharges

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  1. Influence of the Dynamic Ergodic Divertor on TEXTORDischarges K.H. Finken, Y. Xu, S.S. Abdullaev, M. Jakubowski, M. Lehnen, M. F. M. de Bock, S. Bozhenkov, S. Brezinsek, C. Busch, I.G.J. Classen, J.W. Coenen, D. Harting, M. von Hellermann, S. Jachmich, R.J.E. Jaspers, Y. Kikuchi, A. Krämer-Flecken, M. Mitri, P. Peleman, Pospieszczyk, D. Reiser, D. Reiter, U. Samm, D. Schega, O. Schmitz, S. Soldatov, B. Unterberg, M. Van Schoor, M. Vergote, R.R. Weynants, R. Wolf, O.Zimmermann, and the TEXTOR Team

  2. DED topics: Helical divertor Field line and plasma topology Impurity shielding Field line penetration Interaction with MHD

  3. Outline: • Introduction to DED • Effect of the perturbation field on ELMs • Improved confinement by DED • Turbulence reduction by DED • Summary

  4. 16 DED coils Max. current per coil: 15 kA DC and AC up to: 10 kHz

  5. m = 12, n = 4 m = 3, n = 1 m = 6, n = 2 Base modes for DED operation

  6. H-mode characterization and ELM suppression by DED-field

  7. TEXTOR # 97315 DED 15 ALT Ha - drop 10 / a.u. a H 5 0 0 0.5 1 1.5 2 2.5 3 10 n ~ 500 Hz / a.u. 5 a H 0 2.5 2.505 2.51 2.515 2.52 time / s Characterization of H-mode Basic scenario: Ip= 240 kA/ Bt= 1.2 T-1.4 T, plasma shifted to HFS (R=1.68m / a=0.4m)

  8. Power threshold about twice the L-H threshold in divertor tokamaks – “typical” for limiter H-modes # 97300/1, 97312/14/15, # 98296, 98491, 99595 2 Predictive RITM code calculations for 1.3 MW heating power and H/ (H+D) = 40% and TEXTOR data D. Kalupin, M. Tokar # 97314 continued ELM - 1.8 signature over 1s / W x 106 1.6 sep 1.4 P o no DED + with DED # 98491 (L-H transition) 1.2 with ELM signature w./o. ELM signature 1 "dithering" 0.8 4 5 6 7 8 9 10 P / W 5 L-H thresh, IAEA96 x 10

  9. 1500 1000 / Hz ELM n 500 0 1 1.2 1.4 1.6 1.8 2 b N ELM frequencies TEXTOR limiter H-mode

  10. Evolution of edge pressure HFSTEXTOR # 97315 (thermal He beam) H- L – transition with DED R= 1.3 m L-H – transition

  11. TEXTOR # 97315 2 / a.u. 1 a D 0 2.2 2.4 2.6 2.8 3 15 / kA 10 5 DED I 0 2.2 2.4 2.6 2.8 3 1000 DED induced L-H transition back transition / m/s (CIII) 0 q -1000 v 2.2 2.4 2.6 2.8 3 time / s ELM mitigation in 12/4 base mode ELM suppression starts at 3 kA

  12. ELM mitigation in 12/4 base mode DED threshold: 3 kA

  13. TEXTOR # 98296 (I = 250 kA / B = 1.4 T, R= 1.72 m, a= 0.44 m) p T 3 2 1 19 -3 n / 10 m 0 e I / kA (AC 1 kHz) DED -1 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 6 x 10 4 / W 2 tot P 0 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 5 / a.u. a D 0 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 2 ~0.9) r 1 / a.u. ( 0 e T 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 time / s ELM mitigation in AC 3/1 base mode

  14. TEXTOR # 97300/1, 97312/14/15 / s 0.025 H89= 1.25 0.024 E t 0.023 0.022 H89=1 0.021 0.02 0.019 with ELM signature 0.018 w./o. ELM signature 0.017 o no DED + with DED 0.016 R= 1.68m 0.015 0.015 0.02 0.025 t / s E, ITERH89P Improvement of energy confinement during H-mode modest some reduction of energy confinement with DED

  15. Confinement change with DED in m/n = 6/2 base mode

  16. Best conditions have been observed for • strongly inward shifted plasmas • low density plasmas, low collisionality • Co-NBI heating • Ip = 310 kA; Bt = 1.9 T • IDED = 7.5 kA

  17. Stepwise density increase during DED-ramps

  18. Density profile Density time trace

  19. pressure time trace

  20. Comparison of pressure profiles for discharges with and without DED (from Thomson scattering) Ne Ne*Te

  21. Related effects Plasma rotation Heat pattern and electric potential Poloidal rotation CIII

  22. Field line structure at density step Poincaré plot Laminar plot q=2.0 island Starting ergodization of q=2 surface

  23. Effect of the DED on turbulence

  24. Effect of the DED on turbulence Turbulence-probe 3 strokes during one discharge

  25. Turbulence-probe head (RS-probe) • “Reynolds stress probe”: • measures: • floating and plasma potential • electron temperature • electron density and particle flux • main feature: • small pins dedicated to measure • fluctuations of poloidal and radial velocity • => Reynolds stress • Zonal flows • min radius: 42 cm (217 cm) Tungsten pins (d = 1-2 mm) Boron-nitride body (isolator)

  26. Equilibrium profiles (6/2 DED) Before DED  DED ramp DED plateau  a=45.7cm a=45.7cm Ergodic zone Te Vf Er ne r (cm) r (cm)

  27. Turbulence with / without DED ~ ~  in 3/1 DED  in 6/2 DED Before DED  DED ramp DED plateau  Inward flux with DED Ergodic zone a lc (cm) S(f) Coherent modes reduced lcr (cm) Size of turbulent cells reduced r (cm)

  28. Summary On TEXTOR, a limiter H-mode has been obtained. The ELMs were reduced at moderate ergodization levels. 12/4 and AC 3/1 base modes have been applied successfully. The energy confinement is slightly reduced by DED. Confinement improvements have been observed for some plasma / DED conditions. Best conditions were found for strongly heated low density plasmas shifted strongly towards the HFS (DED). Improvement has a resonance character with respect to q(a) and the DED-current.

  29. Summary continued Probe measurements: Strong effect of DED on equilibrium values of F(r) and Er. Turbulent flux reverses sign. Size of large turbulent structures reduced. Coherent modes strongly reduced.

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