21 st IAEA Fusion Energy Conference Summary Innovative Concepts Confinement & performance

1. 21st IAEA Fusion Energy ConferenceSummaryInnovative ConceptsConfinement & performance Jerome PAMELA, EFDA With the kind support of A.Becoulet (CEA), D.Borba (EFDA) and R.Kamendje (EFDA)

2. Innovative Concepts- Z-pinches- field reversed configurations- spheromac formation by steady helicity injection (HIT-SI) - magnetic dipoles (or Ring Trap): SC rings levitated / several seconds to minutes operation X-Divertor concept proposed to enhance the divertor thermal capacity RT-1 / study of Jupiter’s magnetosphere

3. Mirror experiments GOL3 (RF): Te ~2-4 keV ne ~ 3 1020 m-3 nTt ~1018 m-3 s keV Potential for testing PFCs (ELMs, disrup. simulation) tbc. GDT (RF): Te ~0.2 keV ne ~ 5 1019 m-3 With 4MW NB Agreement with theory Hanbit (US): Test divertor stabilising m=-1 MHD flute-instab. X-Ray Tomography GAMMA 10 (Japan) Turbulence Ti Increase With ExB Sheared Layer (b) Without ECH Produced Layer Radial Transport Barrier i/i-classic Diffusivity i Suppress Cylindrical ExB Sheared Flow due to off-axis ECH Controls Radial Transport Barrier, which improves Core Plasma confinement. ECH (250 kW) raises Te0=750 eV with Ti^0=6.5 keV andTill0=2.5 keV T. Choet al.EX/P7-14;Phys.Rev.Lett. 97 (2006)055001;Phys.Rev.Lett. 94 (2005)085002

4. Toroidal Magnetic Fusion DevicesMain recent hardware improvements on Tokamaks • AUG • W-coverage extended to 85% of plasma facing components • New integrated control and data acquisition system • diagnostics • MAST • JET-type NB PINI • Pellet injection • Diagnostics and control systems • Divertor upgrade • NSTX • Modified divertor PF coils (high d) • Diagnostics and control • C-Mod • boronisation • FTU • Li Liquid Limiter • EAST started • JT60 • FST inserts • JET • MKII-HD Divertor (high delat, 40MW capability) • NB heating • Several diagnostics • DIII-D • NB reconfigured • Lower divertor modification allowing balanced DN operation with imporved density control • diagnostics

5. ASIPP EAST first plasma on 26 September 2006 • Largest operating fully SC Divertor tokamak • Nominal parameters Bt=3.5T, Ip= 1MA, R=1.75m, a=0.4m, single/double null • 4.5 s shots already achieved

6. Without FSTs With FSTs JT60-U: ripple reduction by Ferritic Steel Tiles Installation of Ferritic Steel Tiles => Reduction of fast ion losses by 1/2~1/3 at 1.6T • Larger Pabs at given Pin => smaller required NB units for given bN => better flexibility in NBI combination => better flexibility of torque profile • Smaller inward Er => less ctr-rotation

7. AUG :85% W plasma facing components ● in 2005 “thin” W coating of - 4 guard limiters at LFS (water cooled) - 8 ICRH antenna side limiters - top of bottom PSL - roof baffle ● in 2006 - upper and lower ICRH limiters - W coated bottom target tiles (200 mm) full tungsten machine in 2007

8. ITER plasma shape accessible at high current (up to 3.5 MA) 40 MW power capability Height (m) R (m) JET: Divertor modified Up to 32 MW plasma heating achieved recently

9. DIII-D: Reoriented NB box allows more relevant balanced injection heating

10. Transport/Confinement Physics ExperimentsSpecific Stellarator studies • Comparison of quasi-helically symmetric (QHS) configuration to broken symmetric configurations on HSX / confirmation of improved confinement in QHS configuration • Extensive Core Electron Root Confinement (CERC) studies in helical devices (CHS, LHD, TJ-II and W7-AS) / collisionality threshold depends on magnetic configuration and ECH power • Studies of effective ripple on confinement (Heliotron-J, LHD) • Other studies reported below

11. LHD: study on the Confinement in High-b Regime Degradation can be attributed to global dependence on effective helical ripple to the neoclassical transport not on MHD effect  Degradation in high b regime will be improved by dynamic Rax control by vertical field in nearest future Outward shift of plasma by Shafranov shift causes an increase of the effective helical ripple

12. Transport/Confinement Physics ExperimentsRotation and Confinement

13. TORE SUPRA Tore Supra: toroidal rotation observed with ICRH in correlation with confinement improvement (L-Mode) • Suggests sheared rotation • Could explain confinement improvement through ITG and TE modesstabilization (Kinezero)

14. JT-60U 1.1 1 0.9 w FSTs co-NB 0.8 co-rotation helps to form stronger Te-ITB bal- ctr- 0.7 HH98(y,2) co- bal- ctr- w/o FSTs -300 -200 -100 0 100 200 VT(r/a=0.2) (km/s) JT60-U: Pedestal parameters and confinement improved with co-rotation in H-mode

15. Ion temperature profiles during ITB formation Poloidal velocity from charge exchange, during ITB formation V (km/s) Ti (keV) Rmid(m) Rmid(m) Measured poloidal velocity in ITB layer (60km/s) highly anomalous, far larger than neoclassical (~5-10km/s) JET: measured poloidal velocity in ITB • Er and ExB shear much larger with measured Vq • Weiland model with measured Vq (rather than neoclassical) matches experimentbetter

16. DIII-D profiles with high / low rotation compared to modelling confirm importance of ExB shear for ITBs

17. DIII-D: Transport physics sensitive to applied torque / Rotation

18. Transport/Confinement Physics ExperimentsTurbulent transport: TEM, ITG, ETG

19. Stronger edge cooling Te rise delayed ne increases simultaneity LHD: extensive parametric study of non-local Te rise (cold pulse propagation) / anomalous transport behaviour similar to that observed on tokamaks / usefully extends experimental data base to test ITG-based models Larger dTe/dt

20. OH ECH heated plasmas TCV: Influence of plasma triangularity on transport (L-mode) Gyro-fluid, gyro-kinetic models TEM dominant transport (mixing length) predicted to decrease with d, as observed

21. AUG: anomalous transport studies Pure electron heating: threshold for TEM at R/LTe3 (Similar observation on JET) ITG-TEM transition (Er measured at r=0.7): TEM suppressed at high collisionality Results reproduced by simulation (GS2)

22. ECH heated plasmasT10 : TEM dominates turbulent transport at low collisionalities

23. C-Mod: TEM turbulence density fluctuation spectra measured during ITB (ICRH heating) & reproduced by GS2 simulation

24. ELMs NSTX: new high resolution tangential microwave scattering system (280 GHz) allows high resolution of turbulence measurement • Scattering system measures reduced dn/n from upper ITG/TEM to ETG kr ranges during H-mode • Results consistent with modelling • ITG/TEM stable during H-phase • ETG modes could be important / • Lower growth rate during H-mode

25. Transport/Confinement Physics ExperimentsETB & ITB studies

26. H98(y,2) Edge Transport Barrier: Er transitions at plasma edge in tokamaks and helical devices AUG: Negative Er well observed at ETB, increases with confinement improvement - coincides with H-mode barrier gradient - Doppler reflectometry AUG AUG CHS: Negative radial electric field of Er ~ 10 kV/m observed with ETB formation CHS

27. FTU: ITBs in L-mode / reduced ion thermal diffusivity

28. 60 200 150 Pulse No: 62077 40 ITB [eV] 100 Amplitude 20 50 [deg] ] 3 0 0 Phase 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 MW/m Fast wave 2 [10 Mode conversion RF P b) R[m] JET: Te modulation experiments show ITB as a narrow layer with reduced heat diffusivity • Modulated RF power deposited either side of ITB (at centre and at R=3.6m) • Heat wave propagates towards ITB from both sides • Heat wave amplitude (red) damped strongly when wave reaches ITB • Phase (blue) rises when heat wave approaches ITB, showing heat wave slows down • ITB is a narrow layer with reduced heat diffusivity • Indication of region with turbulence stabilised and loss of stiffness

29. Transport/Confinement Physics ExperimentsITB studies:role of rational q surfaces

30. ne Ti Te Ip TJ-II: role of low order rationals in core transitions SXR profiles • CERC triggered by the n=4/m=2 rational • Changes in both Te and Ti. • The SXR tomography diagnostic shows a flattening of the profiles localized around  ≈ 0.4 with a m=2 poloidal structure. • The rational must be inside the plasma to trigger the transition.

31. JET: ITB forms when qmin exists and approaches (rather than reaches) an integer value Te at various major radii, R, showing formation of an ITB ITB formation slightly ahead of Alfvén Cascades (marking qmin= integer) Pulse No: 61347 qmin reaches 2 Start of ITB formation tAC-tITB(s) Te (keV) Case number Time (s) • Alfvén cascades seen simultaneously on microwave interferometer, O-mode interferometer, X-mode reflectometer and magnetic probe • ITB formation starts before q=2 surface enters plasma

32. DIII-D: similar observations / explained by GYRO simulation (zonal flows) Zonal flow structures with significant radial extent / ExB shear flow needed M.E.Austin, University of Texas

33. Transport/Confinement Physics ExperimentsTurbulence and Zonal Flows

34. - a large number of experimental and theoretical contributions- an overview by Pr. Fujisawa ZONAL FLOWS / A HIGHLIGHT An example of extremely fruitful interaction between: Forward looking theoreticians Other scientific Communities “Smaller” devices of all type (tokamaks, helical devices etc.) flexible and well diagnosed Larger devices (driving specific diagnostics improvements)

35. Devices Discoveries ASDEX-U (reflectometry) i) zonal structure CHS(HIBP) CASTOR (probes) symmetry (m=n=0) a finite radial wavelength CLD (probes) CSDX (probes) DIIID (BES) H1 (probes) ii) nonlinear coupling with turbulence HT-7 (probes) HL-2A (probes) JIPPT-IIU (HIBP) JFT-2M(HIBP&probes) LMD (probes) iii) effects on transport TEXT-U (HIBP) T-10 (HIBP) TJ-II(probes) TJ-K(probes) Zonal Flow Experiments (Pr. Fujisawa Talk) A challenge to experimentalists - electric field or flow measurements in high temporal and spatial resolution More than a dozen papers have been published as a PPCF cluster (2006).

36. HL-2A , DIII-D, TJ-II :- Toroidal structure of Geodesic Acoustic Modes (GAMs) observed- GAM interacts non-linearly with ambient turbulence and drives forward cascade of energy to high frequency- energy transfer between global (parallel) flows and turbulence also observed on helical devices HL-2A DIII-D TJ-II

37. ~ Power ( E/∇T) confinement is improved without shear Potential (or Temperature) 10-3 0 radius 1 Common ITB in helical plasmas CHS: Energy partition between ZF and Turbulence without/with ITB CHS two Heavy Ion Beam Probes = powerful core plasma diagnostic At a radius without mean Er-shear inside the barrier No ITB Clear difference in energy partition ITB A larger fraction of zonal flows contributes to confinement improvement inside the barrier! Importance ofzonal flows on confinement is demonstrated.

38. Extensive studies on several machinesAUG: study of parametric dependence of Geodesic Acoustic Modes (GAMs)

39. Transport/Confinement Physics ExperimentsScaling

40. MAST and NSTX: scaling studies NSTX & MAST in ITPA data base: tE ~ e1.03 as compared to t98y,2 ~ e0.58 Dedicated scans on NSTX show tE ~ BT0.9 Ip0.4  -  interplay in H-mode MAST-DIII-D comparison Matching plasma shape, poloidal p*, p and an/T2 provides a constraint on the exponents in the power law scaling: Constraint is consistent with: - gyro-Bohm Scaling (x = -3) - weakly favourable collisionality scaling (as observed in MAST & other devices) -  -  interplay in accord with that derived from the database analysis

41. Confinement in LHD Improved w.r.t. ISS95 scaling Energy confinement time exceeding the ISS95 scaling

42. TORE SUPRA scaling experiments in L mode :favourable weak dependence on b as seen in H-mode (JET & DIII-D 20th FEC) • Weak  degradation.  exponent: ~ -0.2 • ITER L-mode scaling -1.4 • Supported by density fluctuation measurements

43. Transport/Confinement Physics ExperimentsDensity peaking

44. Significant density peaking expected on ITER • TCV: Stationary ELMy H-modes, eITBs • Density profiles are peaked despite pure electron heating and no core source Te/Ti~2 and bN~2 • Peaking requires anomalous particle pinch / under investigation by theoreticians n0/<n>vol ITER • Scaling of density peaking to ITER • ne0/<ne> ~ 1.4 Favourable for fusion power, bootstrap fraction, density limit eff Combined JET-AUG database on density peaking in ITER Baseline ELMy H-modes / reduced colinearities between physics variables • Impact on impurities requires full assessment

45. 58144 58149 Minority (ion) heating (MH) Normalised Ni profile Mode conversion (electron) heating (MC) 100 r/a 10 peaking ofcW 1 0.2 0 0.1 PECRH/Ptot H-mode Core impurity peaking can be controlled with central electron heating Transport of impurities is turbulent JET AUG Turbulent transport models show peaking dependence on Z and anomalous behaviour of high Z impurities Transition ITG to TEM could explain Ni peaking on JET

46. Long pulses, steady state and Real Time Control (performance)

47. JT-60U slow decrease of Wp & Ip JT60-U : Fully Bootstrap-Driven Discharge Ip = 510 kA was maintained for 1.3s with fBS ~ 1 (with net INB = -35kA) Comment: q95 still very high (>10) => higher current demonstration needed

48. TRANSP non-inductive current fractions 116313G12 NSTX: progress in current sustainment NBCD and p provide up to 65% of Ip • Relative to 2004,High bN  H89Pnow sustained2  longer Long Pulse Operation is a challenging issue for STs

49. LHD: 54-Minute plasma operation Record of input energy 1.6 GJ achieved on LHD (Tore Supra 1 GJ at 20th FEC) Rax= 3.67-3.7m, B=2.75T, PICRF= 600-380 kW, PECH=110 kW ALSO: 31-minute long discharge with 680 kW ICRH power, Te(0) and Ti (0) of 2 keV at ne of 0.81019m-3

50. HT-7: steady state operation Steady-state alternating current (AC) operation Ip=125kA ne(0)= 1.5-2.51019m-3 Te= 500 eV 30 seconds with LH 53 seconds w.o. LH ALSO: Steady state “standard” long pulse achieved > 6 minutes Ip=60kA ne(0)= 0.8-1 1019m-3 PLH= 150kW