1PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Non-linear oscillations and synergy effects in non-inductive plasma regimes on Tore Supra G. Giruzzi Association Euratom-CEA sur la Fusion CEA/DSM/DRFC, CEA/Cadarache (FRANCE) Acknowledgements: J.F. Artaud, A. Bruschi, R. Dumont, G. Granucci, F. Imbeaux, J.L. Ségui,and the Tore Supra Team

2PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Physics of discharges at E || ~ 0 Discharges at vanishing Ohmic field. Requirements: – a powerful non-inductive CD system – implementation of long-pulse technology on PFC – discharges much longer than the full resistive time Discharges at vanishing Ohmic field. Main properties: – particle transport: no Ware pinch (  Hoang et al., Phys. Rev. Lett. 90, (2003)) – absence of the strong Ohmic constraint on current profile  q profile is dominated by non-linearities in wave-plasma interaction, bootstrap current, heat transport, interplay with MHD....  control of non-inductive discharges

3PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Summary of the talk Illustration of the physics at E || ~ 0 by two noticeable examples on Tore Supra experiments: – Non-linear T e oscillations: discovery of the O-regime (  Giruzzi et al., Phys. Rev. Lett. 91, (2003)) – ECCD experiments in LHCD plasmas: synergy effects

4PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Non-linear temperature oscillations: the O-regime

5PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 What is the O-regime ? (ECE)

6PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 These oscillations are not MHD Magnetic axis low frequency (~ 10 Hz) no helical structure (m=0, n=0, from soft X-ray tomography) no correlation with MHD signals (Mirnov coils) TeTe

7PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 The best shots are in the O-regime Injected energy record shot: 0.75 GJ 4 min. 25 s

8PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 nl (10 19 m -2 ) P LH (MW) T e (  = ) (keV) Oscillations during LH ramp-up

9PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 nl (10 19 m -2 ) P LH (MW) T e (  = 0) (keV) nl (10 19 m -2 ) T e (  = 0) (keV) … or during density ramp-up

10PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 nl (10 19 m -3 ) P LH (MW) T e (  = 0) (keV) V loop (V) An "anomalous" case (V loop  0) V loop ~ 175 mV n || = 1.5

11PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 n || ≈ 1.8 no ECRH Oscillations amplitude vs frequency

12PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003  T e peaked = 62.2 mV  T e hollow = 9.3 mV Oscillations amplitude vs V loop n || = 1.5 ICRH

13PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 V loop (V) P EC (MW) P LH (MW) V loop ≠ 0 Transition to O-regime by co-ECCD T e (  = ) (keV) V loop (V) P EC (MW) P LH (MW) T e (  = ) (keV) V loop = 0

14PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/ or by counter-ECCD at  = 0.2 nl (10 19 m -2 ) P LH (MW) T e (  = 0) (keV) ECRH phase T e (  = 0) (keV) P EC = 0.4 MW

15PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 A short ECCD trigger is sufficient T e (keV) ECE ECCD P LH (MW)

16PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 q(r) T e (r) T e0 (keV) EC phase Current diffusion analysis (CRONOS) link with the q profile (shear and/or rational surface) link with confinement oscillations  regime of intermediate confinement

17PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 – appearance after a long time (  E || diffusion) – appearance during transient phases (LH or density ramp-up) – link with V loop level and n || of LH waves – link with the hard X-ray profile width T e (0) (keV) Hard X-ray profile T e oscillations are linked with j(r) –link with q profile and confinement: the O-regime is an incomplete transition to improved confinement

18PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Lotka-Volterra equations Used for modelling populations in ecosystems 2 coupled nonlinear equations, periodic solutions J = predator; T = prey ? Predator-prey systems

19PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 When current chases temperature Resistive diffusion and heat transport equations:... have similarities with the Lotka-Volterra equations:

20PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Oscillations reproduced by CRONOS coupled resistive and heat diffusion equations have periodic solutions if: j LH (r)  j(r)T e (r)  e is a function of j (e.g., improved confinement for negative shear) Outputs of the CRONOS code resistive diffusion heat transport self-cons. equilibrium j LH (r)  j(r)T e (r)

21PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Profiles during an oscillation q(  ) Te()Te() s(  )

22PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA 6/10/2003 Conclusions on O-regime A new tokamak plasma regime Predator-prey system with a distinctive feature: non-linearity in a diffusive term Challenging application for the CRONOS code Can this be useful ? (e.g.: periodic q profile movements could prevent MHD)

23PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Combined Electron Cyclotron and Lower Hybrid Current Drive Experiments on Tore Supra: the Synergy Effect

24PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Why to combine LH and EC waves ? LH waves: best CD efficiency limited control capability (multi-junction launcher) EC waves: much lower CD efficiency (waiting for reactor T e ) good control capability (localized absorption) Combination of the two suggested since the early '80s I. Fidone et al., Phys. Fluids 27 (1984) 2468 Successful current ramp-up experiments with LH+EC WT-2:A. Ando et al., Phys. Rev. Lett. 56 (1986) 2180 JFT-2M: T. Yamamoto et al., Phys. Rev. Lett. 58 (1987) 2220 WT-3: T. Maekawa et al., Phys. Rev. Lett. 70 (1993) 2561 Kinetic calculations point out a possible synergy I. Fidone et al., Nuclear Fusion 27 (1987) 579

25PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 What is the synergy ? A definition: I LH+EC > I LH + I EC Simple physical picture: 1)EC waves heat electrons at the lower end of the LH tail (~ 3v th ) 2)LH waves push them to high parallel energies 3)As a result, v || >> 3v th  CD efficiency improved LH controls the efficiency EC controls the j profile parallel distribution

26PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Attempts to demonstrate synergy WT-3 and JFT-2M ramp-up experiments: effect of E || and hot conductivity transient regimes fast electron confinement issue  synergy cannot be assessed or quantified Steady CD experiments: Versator- II (J. Colborn et al., Nucl. Fusion 38 (1998) 783) TdeV (Côté et al., 25th EPS Conf. 22C (1998) 1336)  inconclusive or negative results

27PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Exploiting long shots on TS T e (0) (keV) transformer flux (Wb) P LH (MW) n l (10 19 m -2 ) I p (MA) LHCD plasma target: V loop = 0 (transf. flux kept constant) I p kept constant (feedback by LH power) density kept constant (feedback by gas puff)

28PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 P LH decreases during ECCD phase T e (0) (keV) P LH (MW) n l (10 19 m -2 ) T e (  =0.1) (keV) T e (  =0.25) (keV) ECCD phase P EC = 0.7 MW (two gyrotrons), toroidal angle +24° LH and EC waves absorbed at same location 2 improvements: core confinement ECCD efficiency

29PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Core confinement improved after ECCD before ECCD  e (m 2 /s) before ECCD after ECCD q(  ) before ECCD after ECCD

30PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 P LH =0.5 MW replaced by P EC =0.7 MW P LH (MW) transformer flux (Wb) line-int. density (10 19 m -2 ) plasma current (MA) ECCD phase  P LH ≈ 0.5 MW

31PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Proof of synergy effect  I = (I p -I bs )  P LH / P LH  P LH = 0.5 MW   I ≈ 80 kA predicted I EC = 22 kA. Enhancement of LHCD efficiency  LH. Possible effects:  LH increases with I p. Here, I p constant  LH increases with. Here, in the EC phase increases by 5 % only with respect to the phase after EC enhancement of I bs. NEOCLASS computations yield negligible difference LH+EC phase LH phase, post-EC

32PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Variations of EC power deposition Variations of: toroidal angles poloidal angles Result in variations of:  EC = r EC /a (EC power deposition location) (T e averaged over EC power deposition) P LH (W/cm 3 )

33PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003  I well beyond computed I EC linear current (computed) synergy current (measured)  tor = +28°,+25°  tor = +24°,+24°

34PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 ECCD theory is reliable ECCD theory in excellent agreement with DIII-D experiments (Petty et al., Nucl. Fus. 42 (2002) 1366)

35PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Synergy factor: F syn =  I/I EC Comparison with kinetic theory (3-D Fokker-Planck code  G. Giruzzi, PPCF 35 (1993) A123 )

36PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 D LH +D EC in the u || -u  plane Overlap of the two interactions in both real and momentum space is a necessary condition for synergy F syn ~ 4F syn ~ 1

37PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 EC absorbed power in u || -u  space with LH F syn ≈ 1 F syn ≈ 4 without LH

38PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Conclusions on LH+EC experiments LH power replaced by EC power of the same order: an experimental fact Improvement of CD efficiency difficult to explain by other effects than synergy Kinetic calculations of the synergy factor in excellent agreement with experiments Dependence of the synergy factor on physical parameters still to be explored and understood

39PPPL G. Giruzzi Association Euratom-Cea TORE SUPRA Association Euratom-Cea TORE SUPRA 6/10/2003 Prospects Characterization of the O - regime  dedicated experimental studies  mathematical properties  use properties of the O-regime to constrain transport models Control of LHCD discharges at V loop = 0 by ECCD  experimental study of system non-linearities  feedback control of q and T e Establishment and control of electron ITB regimes