1. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20021/25 Physics of ITB’s: Recent results from experiments A.C.C. Sips Max-Planck-Institut für Plasmaphysik, Euratom Assoziation, Boltzmannstrasse 2, Garching. With contributions from: Y. Baranov 1, C. Challis 1, G. Conway, B. Esposito 2, T. Fujita 3, T. Fukuda 3, P. Gohil 4, C. Greenfield 4, G.T. Hoang 5, G. Huysmans 5, R. Jaspers 6, E. Joffrin 1, N. Kirneva 7, X. Litaudon 5, D. Mazon 5, A. Peeters, E. Quigley, T. Tala 8 and R. Wolf 1 : EURATOM/UKAEA Association, Oxon, UK. 2 : Associazione Euratom-ENEA sulla Fusione, Frascati, Italy. 3 : JAERI, Naka Fusion Research Establishment, Naka, Japan. 4 : General Atomics, San Diego, USA. 5 : Association EURATOM-CEA Cadarache, France. 6 :FOM Instituut voor Plasmafysica Rijnhuizen, The Netherlands. 7 : RRC Kurchatov Institute, Moscow, Russia. 8 : Association Euratom-Tekes, VTT, Espoo, Finland. Max Planck-Institut für Plasmaphysik

2. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20022/25 ITB formation. Current Hole. Electron Barriers. International database. Similarity experiments. Sustainment and control. ITB`s with quiesent edge (QDB). Outline  However, we must keep in mind where we need to go !!! Fukuda – EPS ´02 „Transport Barriers provide great opportunities to study the broad dynamics in fusion science“ Schema della proporzioni Physics Scenario development Reactor application

3. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20023/25 ITB scenario – Barrier formation LHCD power level is varied to change initial q-profile Challis, Tala – PPCF ´02 Reversed shear, more NBI torque favours ITB formation. Challis - PPCF ´02 ITB Strong ITB Peak  * Te =  s /L Te

4. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20024/25 ITB scenario – Barrier formation Esposito – EPS ´02 Strong reversed shear Weak shear Turbulence is suppressed when  ExB >  m, but well defined region with s close to 0 is important. ITB´s start near s=0 O.II.12, dynamics of e-ITB´s and ion ITB´s shear ITB Time (s) electrons ions T e (keV)

5. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20025/25 ITB formation: synergy between s and ExB shearing rate Before ITB After ITB  ExB /  ITG Magnetic shear s Tala – PPCC ´01 In modeling the experimental data: Bohm/GyroBohm empirical model, using  (–0.14+s-1.47  ExB /  m ) (O.II.11) Simulation of JET data with the Weiland model show that the density gradient term dominates over the ExB shearing rate (T. Tala, PPCF ´02).  m  f(s), f(s) = 0.42 s + 1.37 for JT-60U JT-60U Fukuda – EPS ´02

6. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20026/25 Barrier formation: ASDEX Upgade results ASDEX Upgrade Formation of an ITB at low n e, applying the NBI power in one step. Good, transient performance: H 89L =3.4,  N =4.

7. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20027/25 Barrier position ASDEX Upgrade (E. Quigley –EPS ´02) The foot of the barrier expands to the positive shear region. This is important for the alignment of j boot with j tot. Litaudon – ITPA ´02 weak shear reversed shear  s /L Te  1.4 x 10 -2  q=3] shear Normalised poloidal flux radius

8. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20028/25 JT-60U: EC preheat is used, to create a reversed shear target and try to expand the ITB radius, Fujita – PRL `01 JET: LHCD is used during the current ramp phase at low density, Hawkes – PRL `01 Current Hole, observation and explanation Current Hole Strongly reversed q-profile before NBI heating starts, which persists during NBI.

9. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 20029/25 Current Hole, explanation for j 0 =0 JET: Experimental observation: j(0)  0 Hawkes – `02, Huysmans – EPS ´02 J(0) (Am -2 ) Global max DlnT m=1 mode grows exponentially as soon as a q=  surface appears. Re-connection flattens the current density to zero inside the q=  surface. JT-60U: current drive with ECCD inside the current hole: extremely difficult. Simulation of the current density on axis with and without the effect of the MHD. Huysmans – EPS ´02 J z (0)

10. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200210/25 Electron transport barriers ASDEX Upgrade Using ECCD: Counter current drive in the centre generates a reversed shear AND a barrier. However, short duration MHD unstable Wolf – IAEA ´00 NEW experiments at ASDEX in 2001/2002. Also ECRH: TCV and FTU... T (keV)

11. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200211/25 Electron transport barriers ASDEX Upgrade new results, Peeters, ´02 More stable regime: Higher Ip (600 kA). Timing of ECCD. Qualitative agreement with theoretical predictions of the TEM stabilisation.

12. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200212/25 Electron transport barriers Textor Jaspers - EPS ´02 T e (r) with 250 kW ECRH alone, modeled with RTP q-comb model for  e. ECRH heating a weakly reversed q(r): At different deposition radii. e-ITB at different rational q´s. e-ITB at q=1e-ITB at q=2.5 * Results on e-ITB´s from FTU (O.II.10) and TCV (O.II.16) follow after this talk * e-ITB,s Tore Surpa, Hoang PRL ´00 T e (keV)  e (m 2 s -1 ) 01.0  2.5

13. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200213/25 Fluctuation measurements in electron ITB´s 2.5 MW LH only, Te > 8keV, ne ~1.5x10 19 m -3 e-ITB forms in negative shear region. No rotation shear.  Turbulence reduction coincides with reduced  e  Low frequencies reduced  not ETG, TEM ? Conway – PPCF ´02  e (m 2 s -1 )

14. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200214/25 ITB scenario – International database Kirneva – 8 th TTF ´02 Data from many experiments, however: Most of the data are for T i /T e > 1. Best confinement data for n e /n GW < 0.6. Confinement increases with ITB radius, favours large radius for q min.  Can these data be used to extrapolate to reactor conditions ?

15. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200215/25 ITB scenario – International database Baranov – APS ´01 Sips & Fukuda – ´01 Combination of 1-D data from various Tokamaks show dependences of access power to ITB: n e (or I p ), and size, weak dependence on Bt.

16. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200216/25 ITB scenario – International database Hoang – EPS ´02 ion ITB electron ITB At same  s, plasmas with stronger reversed shear, require lower input power to form an ITB. At low  * ITB´s form at lower power when confinement is good, easier to create rotation shear, and peaked profiles.

17. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200217/25 ITB scenario – similarity experiments Similarity experiments on ITB formation: ASDEX Upgrade – JET First results from ASDEX Upgrade (to be analysed in detail). JET experiments in 2003 to match dimensionless parameters (q, , *,  *). t=0.942 t=0.968 t=0.994 t=1.072 However, this is the collapse of the ITB, due to the ELM´s !!! ASDEX Upgrade

18. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200218/25 ITB scenario - duration Litaudon – PPCF ´02 LHCD to create and sustain q (r). 2MA/3.4T, q 95 = 5.5. H 89P = 2.0,  p = 1.1,  N = 1.7. Duration = 36  E (e-ITB). Duration = 27  E (i,n e,v tor -ITB). Type III ELM`s at the edge due to high j edge (M. Bécoulet, Y. Sarazin - ´01). I boot  1.0 MA I LHCD  0.5 MA I NBI  0.3 MA #53521 P LHCD [MW] I p [MA] MW keV P NBI P ICRH T io n eo [10 19 m -3 ] D  [a.u.] V s [V] lili T eo

19. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200219/25 NBI ITB scenario – duration, but impurity accumulation MHD collapse, Hender/Hennequin- PPCF High Z impurities: - Accumulate (neo-classical behaviour) (R. Dux – PSI ´02). - Due to continued density peaking accumulation of high Z impurities only becomes worse. - Cause (radiative) collapse.  s /L Te  1.4 x 10 -2 Nickel concentration on axis ITB reforms, what if P ICRH  neutron rate, simulating conditions in a reactor ?

20. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200220/25 ITB scenario – duration and control (Mazon – PPCF ´02) Control at “slightly“ lower performance Pulse 53521 collapses 2x.

21. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200221/25 QDB combines an ITB with ELM free steady state H-mode edge, modulated by MHD activity. Counter NBI only. This also maintains q min > 1 and reversed q (r). Low edge density, due to MHD and divertor cryo pumping. Using counter NBI, this ELM free edge has now been reproduced at ASDEX. (O.I.01) ITB scenario - QDB

22. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200222/25 ITB scenario - QDB Edge pedestal pressure in QDB  Type I ELMy H-mode. More stable compared to L-mode, No ELMs  ITB stays

23. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200223/25 ITB scenario - QDB Also in QDB, high Z impurity accumulation is a problem. Experiments with ECRH in the core in progress (Casper – EPS ´02) 10 15 neutrons/s

24. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200224/25 Some concluding remarks 1.Document differences or similarities on ITB formation: q-profile is crucial to ITB formation. Reversed shear is favourable for ITB formation: extreme is a current hole. For ion-ITB ExB shear is required. Need to improve our models to predict ITB formation in reactor (at least come to a consensus). 2.Compatibility with ELM´s We should document ITB collapse with ELM´s. Type III ELM´s okay, but H factor lower (low edge pedestal pressure). QDB demonstrates that it is possible to combine an H-mode edge with ITB, but only with counter NBI, at low density and peaked n e (r). 3.Impurity accumulation: problem in long pulses In order to avoid this we need a flatter n e (r ), and broader T(r) profiles. Is this compatible with sustaining an ITB ?

25. A.C.C. Sips 9 th EU-US TTF workshop, Córdoba, 9-12 September 200225/25 Finishing with........Open issues 4.High (edge) density: Pellet injection (PEP) or operation at high triangulrity. Why is sustaining an ITB at high density difficult (is it impossible) ? 5.Control in long pulses – good progress has been made: Still need: duration of ITB >> current diffusion time scale. Still need: demonstration of control schemes in reactor relevant conditions. 6.Reactor with  -heating, T e = T i and D-T fuel: Electron heating: ECRH, N-NBI, LHCD and ICRH. Warning: Even the best results in D-D may be difficult to extrapolate to a D-T phase (even without  -power this was difficult in JET & TFTR !). After > 7 years of intensive research – still a long way to go