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Overview of 2006 – 2007 L-H transition studies on JET

Overview of 2006 – 2007 L-H transition studies on JET. Y Andrew CDBM ITPA Meeting, Lausanne, Switzerland 7 – 10 th May 2007.

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Overview of 2006 – 2007 L-H transition studies on JET

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  1. Overview of 2006 – 2007 L-H transition studies on JET Y Andrew CDBM ITPA Meeting, Lausanne, Switzerland 7 – 10th May 2007

  2. Y Andrew1*, NC Hawkes1, Y Martin2, R Sartori3, V Parail1, TM Biewer4, K Crombe5, C Giroud1, A Korotkov1, E de la Luna6, V Naulin7, I Nunes8, G Saibene3, P de Vries1 and JET-EFDA contributors# • Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK • EPFL/CRPP Association Euratom, Lausanne, Switzerland • 3. EFDA Close Support Unit, Garching, 2 Boltzmannstrasse, Garching (DE) Germany • 4. Oak Ridge National Laboratory, Oak Rdige, TN 37831, USA • 5. Department of Applied Physics, Ghent University, Belgium • 6. Associacion Euratom/CIEMAT para Fusion, Madrid, Spain • 7. Risoe National Laboratory Technical University of Denmark, OPL-128, 4000 Roskilde, Denmark • 8. Centro de Fusão Nuclear, Associacão EURATOM-IST, Lisboa, Portugal * yasmin.andrew@jet.uk • # See appendix of M Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu, 2006) IAEA Vienna (2006)

  3. Outline • Background • Effect of new JET Divertor of H-mode Access • H-mode Access with ‘ITER-like’ magnetic configuration • Influence of X-point location • Ip scan • Bt scan • Effect of TF Ripple on H-mode access • Type-III to Type-I ELM access

  4. Experimental Method L-mode H-mode • H-mode threshold measurements performed on JET by ramping the input power by typically 1 MW/s to follow the L-H and H-L transitions • Power threshold is defined as: • Pth = Pin+POH-dWdia/dt • at the transition to H-mode • L-mode density is held constant using feedback control Da Power Wdia Edge ne Edge Ti Edge Vtor Edge Vpol

  5. New Divertor MkII LBSRP MkII SRP HT3 2003 HT3 2006

  6. New Divertor has no effect on Pth • Density scan repeated for HT3 configuration with new divertor

  7. Increasing dlower Proximity of X-point to divertor wall increasing V/SFE/LT 2003 HT3 2003/2006 ITER-like 2006

  8. ITER-like configuration • ITER-like configuration Pth demonstrates weaker density dependence

  9. X-point height scan ITER-like configuration with X-point (a) closer to inner wall and (b) reduced in height (b) (a)

  10. Reduction in Pth #68299 ITER-like optimised #68300 ITER-like innermost X-point #68301 ITER-like lowest X-point Total Input Power Edge Density dlower

  11. Ip scan • Some variation in density with increasing Ip, so observed trend most likely to be the result of density dependence • Need to account for ne dependence of Pth

  12. Bt scan at fixed q95 • Some variation in density with increasing Ip/Bt • Need to account for ne dependence of Pth

  13. TF Ripple – low density Ip/Bt = 2 MA/2.2 T, q95 = 3.7, d ~ 0.2 0.08 % - No Ripple # 69638 1 % Ripple # 69639 No significant difference between L-H transition for ‘No Ripple’ and 1 % Ripple shots at low density 4.3 MW 4.1 MW Total Input Power Edge ne 1.3x1019 m-3 3.70 m 3.83 m Edge Ti

  14. Edge CXRS Lines of Sight # 69638 @ 60s 3.70 m 3.66 m 3.83 m Ti (eV) Mid-plane Radius (m)

  15. TF Ripple – low density Ip/Bt = 2 MA/2.2 T, q95 = 3.7, d ~ 0.2 0.08 % - No Ripple # 69638 1 % Ripple # 69639 Edge ne • ELM Da characteristics different for no-ripple and ripple shots • No significant difference in edge ne during evolution of H-mode between no-ripple and ripple case • Large differences in edge vtor are observed during the H-mode phase • Differences in vtor disappear following the transition back to L-mode vtor 3.66 m 9 km s-1 3.70 m -62 km s-1 vtor 3.83 m vtor

  16. TF Ripple – higher density 4.7 MW #69641 0.08 % ripple #69640 4.6 MW 1 % ripple 4.2 MW #69646 1.3 % ripple Total Input Power Ti ne edge ne

  17. Type-III Type I ELM Threshold ITER-like configuration 2.5 MA/2.7 T #68221 6.5 MW #68221 #68218 7.2 MW #68218 7.9 MW #68220 8.8 MW #68219 #68220 #68216 14.2 MW #68216

  18. Type-III  ELM-free Type III ELMs ELM-free phases #68221 ITER-like Outer Divertor Da • The plasma does not drop out of H-mode • It has ELM-free H-mode phases: • Da signals remains low • ne increases due to lack of ELMs • Wdia increases Edge ne Wdia

  19. Conclusions • Replacement of SRP has no influence on Pth • Pth of ITER-like configuration demonstrates much weaker density dependence • Lowering of X-point height shows more dramatic effect of Pth than inner wall proximity • Three point Ip scan carried out • Four point Bt scan carried out • Valuable set of data has been obtained on H-mode transitions on JET with different levels of Toroidal Field ripple at two different densities • Type-III to Type-I ELM transition studies started

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