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Recent progress in the analysis in the JET hybrid scenario discharges

Recent progress in the analysis in the JET hybrid scenario discharges. J ö rg Hobirk 25 th September 2007 JET Seminar. Thanks to ….

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Recent progress in the analysis in the JET hybrid scenario discharges

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  1. Recent progress in the analysis in the JET hybrid scenario discharges Jörg Hobirk 25th September 2007 JET Seminar

  2. Thanks to … E. Joffrin, I. Voitsekhovitch, O. Zimmermann, M. Brix, C. Giroud, B. Alper, P. Beaumont, A. Boboc, J. Brzozowski, J. Bucalossi, R. Buttery, C. Challis, V. Cocilovo, S. Conroy, Y. Corre, E. de la Luna, P. de Vries, A. Ekedahl, N. Hawkes, S. Jachmich, K. Kirov, H.R. Koslowski, H. Leggate, T. Loarer, P. Lomas, G. Maddison, D. McDonald, A. Meigs, I. Nunes, V. Parail, K. Rantamaki, C. Sozzi, M. Valisa, F. Villone, K.D. Zastrow, M. Zerbini, V. Zoita

  3. OUTLINE • Definitions of a hybrid scenario and examples • Confinement improvement or not? • The q-profile and its consequences • How to proceed? • Summary

  4. q profile in Hybrid is formed, in H-mode relaxed Ip=1.4MA, BT=1.7T

  5. Hybrid mode with q-profile shaping • Hybrid pulse in Mode B with LH preheat • Target q0 after LH preheat and current ramp between 1 and 1.5 and a profile which might be slightly reversed • Low power NBI phase for slow relaxation of q-profile without significant MHD • High power NBI phase to reach target beta and to keep q stationary by adding off-axis bootstrap current, timing depends on MHD stability and q-profile shape

  6. Definitions… From ITER (Green, 2003, PPCF): A hybrid mode of operation, in which a substantial fraction of the plasma current is driven non-inductively by current-drive power and the bootstrap effect, is a promising route towards the establishment of true steady-state modes of operation. A Candidate (ITPA): Improved H-mode from AUG because it combines high q95 with improved confinement properties to that the performance reduction is limited • q0 above (around, slightly below,… ) 1 • No (or mild, or small) sawteeth • Does have mild (no) NTMs • Broad q-profile, low shear • Has improved core (or pedestal, or none) confinement • Operates at high beta (above 1 or 2 or 2.5,….)

  7. 0.5 H=1.5 H=1 ITER advanced scenario Advanced Scenario DIII-D (bNTH<2.7) DIII-D JET (bNTH<2.2) Measured confinement [s] AUG AUG (bNTH<3.2) 0.03 0.5 0.03 Confinement scaling [s] JET Confinement at high normalised pressure No advanced tokamak data in scaling hybrid scenario data different 4 From H-mode database 3 Normalised pressure: bN (TH) 2 ITER H-mode 1 JT-60 JETDIII-DAUG 0 0.001 0.01 Normalised ion Larmor radius Wade Nuc Fus 2005 & Sips Nuc Fus 2007 Confinement dependence at high pressure is an issue E. Joffrin, EPS 2007

  8. On ASDEX Upgrade significant confinement improvement is observed • Target q0 after current ramp between 1 and 1.5 • Low power NBI phase for slow relaxation of q-profile without significant MHD • High power NBI phase to reach target beta • q0 stationary above 1, backed up by non 1/1 MHD activity in plasma • Confinement significantly enhanced without ITB

  9. DIII-D ASDEX Upgrade plasma pressure core ELMs pedestal C. Maggi, EPS 2005 0 a plasma radius Improved confinement in the pedestal ? No clear signs of improved pedestal confinement

  10. Summary of JET hybrid experiments • Most experiments carried out in HT3  high natural density and collisionality • ICRH based experiments done at high field and current  low beta • Current varied between 1.1MA and 2.3MA • TF varied between 1.4 and 3.35T • q95 between 2.7 and 5  Large variation of plasma parameters in data base

  11. Hybrid database extended to low q95 2006-2007 data H-mode (mode D) • Hybrid performance similar to H-mode • Wide range in q95 • Upper and right end of plot power limited q95=2.7 G= H.bN/q952 q95=3.2 q95=4.0 2003 data ~ bp

  12. Filled symbols: fuelled discharges H98 q95=4 q95=3.2 q95=2.7 n/nG Density range expanded for the hybrid regime • Only HT3 pulses included here • Greenwald fraction increased to above unity • Also confinement slightly better than in 2003 • Confinement stays good up to high densities 2002/3 data

  13. Hybrid modes, similar performance to H-modes • Hybrid pulse in Mode B with LH preheat, H-mode pulse in Mode D • Even at higher current li becomes very similar in late phase (q95=2.7) • NBI power slightly higher in H-mode • Energy the same • ELMs the same • Time evolution slightly different  Within measurement accuracy H-mode pulse and hybrid pulse are the same

  14. Profiles of H-mode and Hybrid almost identical

  15. Profiles of H-mode and Hybrid almost identical • All profiles identical (some problems with Ti) • All global values identical • Transport identical?

  16. Confinement does (or not) depend on beta? • Database includes L-modes and type III H-modes • ICRH FP not included in H factor calculation • Lower boundary has a trend, but upper boundary not • Maximum H factors around 1

  17. Summary • An overview over the hybrid experiments in C15-C18 has been given • Hybrid scenario has been extended to low q95=2.7 and to type III ELMs • Going down in q95 increases the normalised performance H89*N/q952 • Differences in performance between hybrid and H-mode small in a one to one comparison

  18. At least one question left… What’s about q?

  19. q < 1 in early phase of hybrid • q below 1 even for 46s • Different q-profile diagnostics agree within reason

  20. q < 1 in early phase of hybrid • What is q=1 radius, n=1 or FB ? • Outer n=3 radius does not fit • Centre of n=3 activity does not agree with plasma centre • q below 1 even for 46s (1.5s after NBI) • q profile does agree with MHD mode locations • Different q-profile diagnostics agree within reason

  21. Hybrid and H-mode q-profiles are identical • Comparison at maximum beta • Comparison at identical timing relative to start of NBI • Sawtooth inversion radius for H-mode not well defined, wrong time (2s early), pivot point is a region • In high heating phase q profiles are identical

  22. Hybrid and H-mode q-profiles are identical • Comparison at maximum beta • Comparison at identical timing relative to start of NBI • Sawtooth inversion radius for H-mode not well defined, wrong time (2s early), pivot point is a region • MSE and FR agree but scatter allows for variation between the shots • In high heating phase q-profiles are similar

  23. q reaches final value early • Different diagnostics and EFIT runs do agree within reason • MHD constrains do not allow to discriminate between EFIT runs • q is constant from 47s on • Occurrence of MHD modes do agree with time dependence

  24. Current diffusion converges q to same state • Similarity in q more pronounced in MSE q • At high beta all q-profile reconstructions agree • Initial q very different, LH preheat vs. long diffusion • Current diffusion quickly results in same q0

  25. MHD similar in hybrids and H-modes • n=1 dominating the spectrum • n=1 consists of sawteeth, fishbones and precursors • n=3 only present in hybrid • Sawteeth stabilised at high beta, likely due to fast particles

  26. q-profile agreement not always good • Here q from MSE and FR do disagree over large part of the profile

  27. FR q-profile depends on density reconstruction • Faraday data good reproduced • Interferometer line integrals good reproduced (ch 2 missing) • Major disagreement between LIDAR and inversion • Density reconstruction plays key role for Faraday Rotation

  28. Only few pulses with q0 larger than 0.9 • Consistency between FR and MSE not always good • Underestimation of q in FR likely because of density reconstruction • 3He and electron heated hybrids have bad data • Most pulses have a more H-mode like q-profile • At higher q0 more disagreement between diagnostics

  29. Confinement drops with q0? • Large scatter of H factors • q’s at low values doubtful • ICRH FP not included in H factor calculation • most high q points have low beta and low triangularity FR • Confinement data has no trend up to 1 • Confinement degrades above 1?

  30. Confinement drops with q0? • Large scatter of H factors • ICRH dominated and most 3He pulses have bad MSE data • Very few points left above 1 MSE • Confinement data has no trend up to 1 • Confinement degrades above 1?

  31. q information before NBI not reliable • Tendency with increasing LH power not clear • Very large scatter, quality of q-profile?

  32. MHD onset and q dependence? • Database includes L-modes and type III H-modes • Threshold is lower with higher starting q? • Threshold for n=3 is lower than n=2

  33. Influence of preheat on final q is small • Data is not sufficiently validated (FR only) for start of the NBI heating • Data might be spoiled by density profile changes FR • Small tendency for q in main heating to increase • Slope very small

  34. Influence of preheat on final q is small • Data is not sufficiently validated (FR only) for start of the NBI heating • Data might be spoiled by density profile changes MSE • Small tendency for q in main heating to increase • Slope very small (y=0.752+0.054*x)

  35. TRANSP qualitatively agrees for late phase • Run starts late (45s) • Central part of profile “frozen” for 1s (Wrong history?) • Time before 45s cannot be reproduced • Data before 45s questionable (density profile evolution) • Drop in central q similar • Agrees for having an early and low final q

  36. Bootstrap current low in first phase • Bootstrap current only 25% • Ohmic current dominates current profile • Total current very peaked

  37. Bootstrap current low in second phase • Bootstrap current only 31%,FP not resulting in BS • Ohmic current still dominates current profile • Total current peaked

  38. On ASDEX Upgrade the q0 is stabilised • Initial drop similar in calculation and measurement • After brief small q phase the experimental q increases • ASTRA simulation does not reproduce time dependence!

  39. S. Günter et al, NF 39, 1999

  40. S. Günter et al, NF 39, 1999

  41. T.A. Casper, IAEA 2006 Chengdu

  42. Higher q95 raises q0 but H98 lower • At q95=5 more easily q>1 obtained • No NTMs/FB or Sawteeth in #69369 • H98=0.8 compared to 0.95 at q95=4 • Same current

  43. Where to go? • q drops very fast  more heating power in first phase ? • BS small  change of density or current? • Additional current drive necessary ? • LH in main heating • Optimise NBI injection (Off-axis) but NBCD in question and duct limits might prevent this • Confinement improvement? q-profile dependence? • Similarity experiment with AUG or DIII-D at high q0 ?

  44. simulations of Hybrid shot 67976 (F. Imbeaux) Experiments by A Ekedahl, K Rantamäki Current diffusion calculated with CRONOS (t=45s to t=53s) LHCD calculated by DELPHINE for: n// = 1.8, n// = 2.3, and no LH in main heating phase. Typical LHCD during main heating • 100% accessibility for n//=2.3. Similar power deposition as n//=1.8 + peak on-axis. • ILH = 160 kA (IP = 1.4MA) n// = 2.3 n// = 1.8 (However, simulations give poor agreement on VLoop and li Need for more non-inductive current and broader current profile, or problem with Zeff ?) LH power deposition at  ~ 0.6-0.8 ILH / IP ~ 10%

  45. Do we have a hybrid at JET? • Operationally? Yes, with LH preheat and different beta phases all criteria are fulfilled • MHD? Yes, most pulses have no or very small sawteeth, NTM activity is there but confinement can still be okey. • Beta? Yes, up to N=3.6 has been reached, discharges are stable against 2/1 • q-profile? No, almost all pulses have a relaxed current profile • Confinement? Indefinite, all pulses have more or less H-mode confinement but connection to q-profile unclear

  46. Thanks to everyone! • Thanks to everyone in the JET team • It was a pleasant time with you • I wish you success with the next campaigns Good bye.

  47. Hybrid modes at low q95~2.7 reach bN~3 • Very good MHD stability at q95=2.7 • Standard type I ELMs • Good confinement • High normalised density • H89*N/q952 =0.72 i.e. almost 2 times ITER target • But sawteeth present, is it a real hybrid? • TF M experiments show that operation up 20% above 4*li is possible without RWM

  48. Total: D+N Strong gas injection is required to get Type III ELM ~1023e.s GIM9: D Type III ELMs Hybrid type III ELM scenario #68515 Reference High D fuelling (D=5×1022) #68532 Radiative feedback (D=5×1022+N=3 ×1022) Radiative feedback: frad=0.7 By Y. Corre TF S1 meeting 7/12/06

  49. How much does it costs? #68507 Reference low D fuelling #68532 N-seeded N 2.5 Price to pay H98Y Zeff (vertical) +2MW Ptot By Y. Corre TF S1 meeting 7/12/06

  50. What is the benefit? Type III: f=500hertz Type I compounds : f~50hertz H (divertor) #68507 Reference #68532 N-seeded By Y. Corre TF S1 meeting 7/12/06

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