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Control of MHD instabilities. Similarities and differences between tokamak and RFP

Control of MHD instabilities. Similarities and differences between tokamak and RFP. V. Igochine, T. Bolzonella, M. Maraschek, W. Suttrop, D.Yadykin. Outline of the talk. Control of MHD instabilities in ASDEX Upgrade Tokamak scenarios and corresponding instabilities

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Control of MHD instabilities. Similarities and differences between tokamak and RFP

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  1. Control of MHD instabilities. Similarities and differences between tokamak and RFP V. Igochine, T. Bolzonella, M. Maraschek, W. Suttrop, D.Yadykin

  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. Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. • ITER scenarios: • H-mode • Improved H-mode • Advanced tokamak scenario RWM NTM, Sawtooth q Safety factor 2 1.5 ρ

  4. Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. • ITER scenarios: • H-mode • Improved H-mode • Advanced tokamak scenario RWM NTM, Sawtooth q Safety factor 2 1.5 ρ

  5. MHD instabilities in conventional scenario 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<Nideal • 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 flat pressure in the island ↓ no bootstrap current ↓ growth of NTM

  6. Possible variant of NTMs suppression • The island position varies during the discharge • We have to match position of the island with current drive position • ASDEX Upgrade (changes of Btor) • Bt 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 EC resonance (3,2) NTM

  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. Possible problem in ITER and their solutions • 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) EC resonance (3,2) NTM Now ITER Current drive is only inside the island

  9. Complete realtime-loop for NTM control • 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

  10. Why do we need to control sawteeth? JET [Sauter et al, PRL, 88, 2002] 15 Magnetics: #58884 only Expanded intime: 15-18s kHz 4/3 3/2 • 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 2/1 0 bN termination SXR/a.u. Fusion born ’s long sawtooth NBI/MW Long sawtooth periods ICRH/MW More likely to trigger NTMs Time (s)

  11. Sawtooth control 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. Example: Change of shear at q=1 with co-ECCD and counter-ECCD in ASDEX Upgrade [A.Mueck, PPCF, 2005]

  12. Complete realtime-loop for NTM and Sawtooth control NTM (1,1), Sawteeth The same system can be used for NTMs and Sawteeth control!

  13. Tokamak scenarios and typical safety factor profiles C. M. Greenfield et. al. • ITER scenarios: • H-mode • Improved H-mode • Advanced tokamak scenario RWM NTM, Sawtooth q Safety factor 2 1.5 ρ

  14. Coils system for ELMs and RWMs control in ASDEX-U END 2009: Installation of 4 Bu and 4 Bl coils. Bu - coils A - coils Bl - coils

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

  16. Comparison of coils geometry in ASDEX-U and ITER ASDEX Upgrade (8x3) ITER (9x3) The coil system is similar to ITER design

  17. Time schedule (from W.Suttrop, Ringberg 2008)

  18. Time schedule (from W.Suttrop, Ringberg 2008) ELM control is one of the main priorities

  19. particles RWM: tens of Hz rotation Plasma flow: kHz rotation RWM is the main common issue for tokamaks and RFPs Coupling: (m, n) (m±1,n) (m±2,n) • 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. RWM rotation experiments in RFX-mod • 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

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

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

  23. RWM rotation experiments in RFX-mod. Next step. Any asymmetry? 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

  24. RWM rotation experiments in RFX-mod. Next step. Any asymmetry? 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

  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.

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