1. RFX workshop /20.01.2009/Valentin Igochine Page 1 Control of MHD instabilities. Similarities and differences between tokamak and RFP V. Igochine, T. Bolzonella, M. Maraschek, W. Suttrop, D.Yadykin

2. RFX workshop /20.01.2009/Valentin Igochine Page 2 Outline of the talk Control of MHD instabilities in ASDEX Upgrade –Tokamak scenarios and corresponding instabilities –Conventional scenario: Neoclassical tearing mode and sawteeth Main stabilizing/destabilizing factors ECCD as a main active control tool ITER requirements for active control –Advanced scenario: Resistive wall mode External coils design in ASDEX Upgrade Present status and start of the operation Control of the RWMs in RFPs in comparison with tokamaks –Similarities and differences in RWM behavior and drive –Open questions in RWM physics Conclusions

3. RFX workshop /20.01.2009/Valentin Igochine Page 3 Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. ITER scenarios: 1.H-mode 2.Improved H-mode 3.Advanced tokamak scenario RWM NTM, Sawtooth ρ q 2 1.5 Safety factor

4. RFX workshop /20.01.2009/Valentin Igochine Page 4 Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. ITER scenarios: 1.H-mode 2.Improved H-mode 3.Advanced tokamak scenario RWM NTM, Sawtooth ρ q 2 1.5 Safety factor

5. RFX workshop /20.01.2009/Valentin Igochine Page 5 Control of MHD instabilities is a key issue to obtain a high-performance plasma MHD instabilities in the core regime Neoclassical Tearing Modes (NTMs) - appear in a high beta plasma - limit the achievable beta at  N <  N ideal Sawtooth Oscillations - have smaller effects on global parameters - are able to trigger an NTM at low  N values Active control is important for both! Control tool: Electron Cyclotron Current Drive (ECCD) - highly localized current drive fill the hole in bootstrap current - flexible ECCD location is necessary MHD instabilities in conventional scenario flat pressure in the island ↓ no bootstrap current ↓ growth of NTM

6. RFX workshop /20.01.2009/Valentin Igochine Page 6 EC resonance The island position varies during the discharge We have to match position of the island with current drive position ASDEX Upgrade (changes of B tor ) B t changes is not possible in superconductor device like ITER DIII-D (moves the plasma radial) No free volume for radial movement in ITER Both variants are not acceptable for ITER! Changes of ECCD deposition system of mirrors to change position of the deposition Foreseen for ITER (3,2) NTM Possible variant of NTMs suppression

7. RFX workshop /20.01.2009/Valentin Igochine Page 7 ASDEX Upgrade enhances its capabilities in this area EC resonance (3,2) NTM Current drive 4 new gyrotrons (1 MW & 10s each) with movable mirror system each. Present status: 1 gyrotron is already installed. The others would be installed in 2009-2010.

8. RFX workshop /20.01.2009/Valentin Igochine Page 8 EC resonance Possible problems in ITER: Deposition width is large Solution: Current drive should be done in O-point only (Maraschek PRL, 2007) Locking of NTM to the wall In line ECE diagnostic to detect the island (F. Volpe) (3,2) NTM Possible problem in ITER and their solutions NowITER Current drive is only inside the island

9. RFX workshop /20.01.2009/Valentin Igochine Page 9 ECE can detect modulated ECRH (every 0.2s 2ms off) MSE migrated to realtime-acquisition and transfers data standard data transfer framework established 80ms realtime TORBEAM for deposition predictions Complete realtime-loop for NTM control

10. RFX workshop /20.01.2009/Valentin Igochine Page 10 Why do we need to control sawteeth? Long Sawteeth have been shown to trigger Neo-classical Tearing Modes –Long Sawteeth  NTMs –Short Sawteeth  Avoid NTMs NTMs degrade plasma confinement Even bigger problem in ITER Time (s) ICRH /MW  NBI /MW termination Magnetics: #58884 only Expanded in time: 15-18s 2/1 3/2 4/3 0 15 kHz long sawtooth SXR /a.u. [Sauter et al, PRL, 88, 2002] Fusion born  ’s Long sawtooth periods More likely to trigger NTMs JET

11. RFX workshop /20.01.2009/Valentin Igochine Page 11 Stability of the (1,1) mode strongly depends from shear at q=1 surface. ECCD is able to destabilize the mode and make more frequent and smaller sawteeth. Sawtooth control Example: Change of shear at q=1 with co-ECCD and counter-ECCD in ASDEX Upgrade [A.Mueck, PPCF, 2005]

12. RFX workshop /20.01.2009/Valentin Igochine Page 12 Complete realtime-loop for NTM and Sawtooth control The same system can be used for NTMs and Sawteeth control! NTM (1,1), Sawteeth

13. RFX workshop /20.01.2009/Valentin Igochine Page 13 Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. ITER scenarios: 1.H-mode 2.Improved H-mode 3.Advanced tokamak scenario RWM NTM, Sawtooth ρ q 2 1.5 Safety factor

14. RFX workshop /20.01.2009/Valentin Igochine Page 14 Bu - coils Bl - coils A - coils END 2009: Installation of 4 Bu and 4 Bl coils. Coils system for ELMs and RWMs control in ASDEX-U

15. RFX workshop /20.01.2009/Valentin Igochine Page 15 Drilling holes for coils in support structures is the most time consuming work which would be done at the end of 2009. Actively cooled coils Coil system design for ASDEX Upgrade

16. RFX workshop /20.01.2009/Valentin Igochine Page 16 ASDEX Upgrade (8x3) ITER (9x3) The coil system is similar to ITER design Comparison of coils geometry in ASDEX-U and ITER

17. RFX workshop /20.01.2009/Valentin Igochine Page 17 Time schedule (from W.Suttrop, Ringberg 2008)

18. RFX workshop /20.01.2009/Valentin Igochine Page 18 ELM control is one of the main priorities Time schedule (from W.Suttrop, Ringberg 2008)

19. RFX workshop /20.01.2009/Valentin Igochine Page 19 RWM: tens of Hz rotation particles Plasma flow: kHz rotation Coupling: (m, n) (m±1,n) (m±2,n) RWM is the main common issue for tokamaks and RFPs RWM is the main common issue for tokamak and RFP RWM is static in RFP and slowly rotates in tokamaks Static RWM typically destroys the plasma confinement Study of RWM locking & unlocking & rotation is important for tokamaks and can be studied in RFPs

20. RFX workshop /20.01.2009/Valentin Igochine Page 20 The RWM can be unlocked in RFPs. Successful experiments on active rotation in RFX-mod. V. Igochine et.al. EPS2008/ T.Bolzonella et.al., PRL, 2008 RWM rotation experiments in RFX-mod

21. RFX workshop /20.01.2009/Valentin Igochine Page 21 Result is in very good agreement with ideal mode assumption. The mode rotation depends on phase shift between feedback and RWM RWM rotation experiments in RFX-mod. Summary.

22. RFX workshop /20.01.2009/Valentin Igochine Page 22 Result is in very good agreement with ideal mode assumption. No effect of plasma rotation up to now. The same rotation in both directions The mode rotation depends on phase shift between feedback and RWM RWM rotation experiments in RFX-mod. Summary.

23. RFX workshop /20.01.2009/Valentin Igochine Page 23 Result is in very good agreement with ideal mode representation. No effect of plasma rotation up to now. Next step: increase frequency of the rotation by changing Δφ Any asymmetry? RWM rotation experiments in RFX-mod. Next step.

24. RFX workshop /20.01.2009/Valentin Igochine Page 24 Result is in very good agreement with ideal mode representation. No effect of plasma rotation up to now. Next step: increase frequency of the rotation by changing Δφ IF YES, THEN PLASMA ROTATION COULD BE IMPORTANT Any asymmetry? RWM rotation experiments in RFX-mod. Next step.

25. RFX workshop /20.01.2009/Valentin Igochine Page 25 Conclusions Different tokamak scenarios require different types of control. RWM physics is a natural common issue for RFPs and Tokamak In spite of several differences the mode is the same and advanced knowledge about mode control can be moved from RFPs to Tokamaks. Further experiments with rotation could help better understand the physics of the RWM.