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Proposals from ITPA TG on MHD, Disruption and Control for ITPA/IEA Joint Experiments in 2004

Proposals from ITPA TG on MHD, Disruption and Control for ITPA/IEA Joint Experiments in 2004 O. Gruber. Based on 2003 proposals. Mainly continuation, partly additional (new) ones (marked in blue ) Questions: ECH assisted start-up at 0.3 V/m

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Proposals from ITPA TG on MHD, Disruption and Control for ITPA/IEA Joint Experiments in 2004

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  1. Proposals from ITPA TG on MHD, Disruption and Control for ITPA/IEA Joint Experiments in 2004 O. Gruber Based on 2003 proposals Mainly continuation, partly additional (new) ones (marked in blue) Questions: ECH assisted start-up at 0.3 V/m (only demonstration discharges up to now)

  2. MDC1 – Pressure & size scaling of gas jets for disr. mitigation Background & previous results Strong gas jets superior to killer pellets: simpler, fast systems, no runaways, Ne/Ar/Kr • - DIII-D: higher gas jet pressure up to 70 bar most effective (uniform radiation, red. loads) • - AUG: reduced force and div. heat loads at much lower gas jet pressures • - JET: higher-Z (Ne, Ar) most effective in reducing VDE forces, but pressure too low. • - JT-60U: Kr most effective (Ar, Xe, Kr) to reduce divertor heat load and avoid runaways • Devices (contacts in bracket) • DIII-D (D Whyte), AUG ( G Pautasso), JET (P Andrew), JT60-U (Y Kawano) • Outline of investigations • - AUG: scaling of pressure effects, routine use combined with prediction scheme, • application in high pressure plasmas, • - JET: higher pressures and faster system for disruption control. • - other tokamaks can contribute (C-MOD, FTU) • Time schedule

  3. MDC2 - Resistive wall mode physics Background & previous results Kink / RWM stability needed in strong ITB / rev. magn. shear plasmas  Influence of wall distance, size scaling of critical rotation frequency, sensitivity of high-beta plasmas to error fields (Resonant error Field Amplification) - RFA expts on JET and comparison with MARS: RFA starts already below no-wall limit - DIII-D: new I-coils allow RWM stabilization at low rotation for 100 ms Devices (contacts in bracket) DIII-D (A Garofalo), JET (T Hender), AUG ( H Zohm), JT60-U (M Takechi) Outline of investigations - JET, DIII-D, AUG: 3 machine comparison still under consideration (wall distance, critical rotation frequ.) - DIII-D, JET: RFA - JT60-U: Studies of effect of rotation on RWM from varying NBI deposition, comparison with other devices under consideration. Active magnetic RWM stabilization - DIII-D: continues with I-coils - JET: possibly with new EFCC´s, comp. with DIII-D Time schedule

  4. MDC3 – NTM physics including error field effects Background & previous results for NTM physics NTMs limit conventional & advanced H-modes (hybrid scenarios) with low central shear  scaling to ITER. - combined bpol scaling in local variables for 3/2 NTM onset for AUG and JET - expts to measure bpol,marg completed on AUG, DIII-D and JET (power ramp-downs): • for 3/2 mode a ~linear scaling with r* is found again •bmarg(2,1)< bmarg (3,2), so once destabilised 2/1 is harder to remove - In rotating plasmas the 2/1 NTM limit can be at ideal wall ß-limit (DIII-D,JET,AUG) - DIII-D: error fields can seed 2/1’s and conversely lower error field threshold near 2/1 NTM limit Devices (contacts in bracket) AUG (M Maraschek),DIII-D (R La Haye), JET (T Hender), Compass-D ( R Buttery), JT60-U (M Takechi) Outline of investigations - AUG, DIII-D, JET: complete bpol,marg scaling for 3/2 and 2/1 mode; supplementing exp. (difficult due to mode locking and disruptions) - DIII-D, JET: “controlled seeding” using error fields and power ramp-ups to establish ßmarg (first done at Compass-D) - JET: expts on error field effects, comp. to DIII-D Time schedule

  5. MDC3 – NTM physics including error field effects Background & previous results Active NTM control needed even in conventional ITER H-mode scenario. - local CD in islands - transition to FIR mode by triggering an 4/3 mode - mitigation by active sawtooth control reducing seed island size (see MDC-5) Stabilization with ECCD in island: - AUG, DIII-D: required power for 2/1 stabilization much higher than for 3/2 mode - DIII-D:´search and suppress` also works for 2/1 NTM - JT-60U: early injection of ECCD is effective for NTM avoidance Frequently Interrupted (FIR) NTMs: - AUG, JET: studies fully integrated showing consistent physics picture - AUG: active transition to FIRs by destab. of 4/3 mode (ECCD) - JET: active transition to FIRs by destab. of 4/3 mode (ICRH) Devices (contacts in bracket) AUG (M Maraschek), DIII-D (R La Haye), JET (T Hender), Compass-D ( R Buttery), JT60-U (M Takechi) Outline of investigations - AUG, DIII-D: early injection of ECCD - JET: NTM avoidance with ICCD, comparison to ECCD method - confinement after ß recovery with active stab. NTMs - AUG, JET, JT60-U: ECCD deposition width vs. island width (necessity of AC FB?) - FIRs also in DIII-D, JT60-U? contributions from STs

  6. MDC3A – Improving NTM modelling / extrapolation to ITER Background & previous results (new proposal) - new approach: mainly analysis, supplementary exp. needed - global or local ß scalings (onset / marginal limit)agree with Rutherford equ. (ß r*), but the single terms are disputable & even the sign of the polarization term is not shure - this leads to large ambiguities in the needed CD / power for active stab. in ITER! Devices (contacts in bracket) see below Outline of investigations 1) agreement on what terms should appear in the Rutherford equation, what are the free parameters, where is theory ok without fudge factors 2) fit w(t) for 3/2 & 2/1 modes in ITER relevant ELMy H-modes (q, n*) to derive coefficients in R.eq. AUG (H Zohm), DIII-D, JET, JT60-U, others? 3) agree on “universal” set of coefficients (???) describing all exp. 4) fit active NTM stabilization experiments with ECCD  possibly one additional coeff. only doable in: AUG (H Zohm), DIII-D, JT60-U 5) use these coefficients for ITER  ICD and width Time schedule

  7. MDC4 - NTMs aspect ratio comparison Background & previous results for NTM physics - help in resolving problems with gen. Rutherford equation for island growth - influence of sawtooth region - high ß effects Same shape and cross-section area, but different A, i.e. q95 differs at same Ip. MAST, AUG: suitable NTM pulses developed on MAST, progress in developing equilibrium scenario for AUG NSTX, DIII-D: NSTX shutdown has delayed aspect ratio comparison Devices (contacts in bracket) see below Outline of investigations - AUG, MAST: exp. scheduled; local q, r*, n* achievable - NSTX, DIII-D: ? Time schedule

  8. MDC5 - Sawtooth control for NTMs suppression Background & previous results - sawtooth control methods tested with ECRH/CD on AUG, DIII-Dand TCV with ICRH on JET, with off-axis NI on AUG - deposition inside or outside inversion radius and with co or ctr CD, resp., - results agree and are in line with theory expectation - AUG: destabilization to high-frequent, small amplitude sawteeth with ECCD rises 3/2 NTM threshold (the converse remains to be tested) - JET: stabilising effect of fast core ions (from ICRH) is countered using a second ICRF near the sawtooth inversion radius (a-stabilisation of sawteeth in ITER) Devices (contacts in bracket) AUG (A Mueck),DIII-D (R La Haye), JET ( O Sauter), TCV (Goodman) Outline of investigations - AUG: further manifestation of stab. effect on NTMs - DIII-D: influence on NTMs? - DIII-D, AUG: counteracting to fast ion stabilization (ICRH) with ECCD near inversion radius (see JET results) Time schedule • -

  9. MDC6 - Error field sideband effects for ITER Mode coupling terms • Background & previous results • Effect of harmonic content on error field driven locked modes showed • differences between COMPASS-D and DIII-D • - Sideband effects measured on DIII-D using I-coils • Devices (contacts in bracket) • DIII-D (R LaHaye), JET ( T Hender) • Outline of investigations • - JET: exp. scheduled for Jan 2004 • - resolving of discrepancies • - AlcC-MOD, JET, DIII-D: scaling of locked mode threshold vs density and Bt • dimensionless scaling  MHD ? • (incl. dimensionless scaling exp.) • Time schedule Ttot(q=2) µ Viscous terms

  10. 1.8 1.8 59223 1.6 59230 MARS code 1.6 59223 59231 1.4 59230 59232 results including 1.4 59435 59231 1.2 kinetic damping MARS 59232 1.2 model - no free 59435 1 RFA parameters. 1 EFA 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0 0 1.4 0 0.2 0.4 0.6 0.8 1 1.2 b / 3.4 l 0 0.2 0.4 0.6 0.8 1 1.2 1.4 MARS with wall beta limit N i b / 3.5 l N i MDC2 - Resistive wall mode physics

  11. D3D: 114781114782 Island width (cm) 2/1 NTM 3/2 NTM bN MDC3 - NTMs including error field effects • 3/2 has lower threshold bN than 2/1 but also stabilises at higher bN • Indicates importance of 2/1 NTM control schemes • Similar result on JET • JET and AUG 3/2 NTM onset bN scalings shows ~linear r* dependence • Initial studies of bp marginal (‘offset’) scalings between AUG, DIII-D and JET show similar ~linear dependence

  12. (2,1) stabilisation needs more power (DIII-D) R.J. La Haye et al., EPS 2003 (3,2) (2,1) • 2/1 mode stabilised with 2.8 MW of ECRH power at bN = 2.1 • 3/2 mode stabilized with 1.4 MW of ECCD at bN = 2.2

  13. MDC3 - NTMs including error field effects Transition to FIR mode by triggering an 4/3 mode with ECCD (AUG) local CD at q=4/3 surface decreases 4/3 stability and provokes FIR NTMs

  14. MDC3 - NTMs including error field effects Pure (3,2) NTM Full symbols: JET Open symbols: ASDEX Upgrade (3,2) coupled to (4,3)  FIR NTM allows high confinement : seen on AUG, JET, DIII-D JT60-U?  confinement improvement at higher b !  regime with 'acceptable' Frequently Inter Rupted NTMs - FIR regime similar in dimensionless param.  transition to FIR NTMs induced by ECCD: local CD at q=4/3 surface destab. 4/3 mode --> provokes FIR NTMs (AUG, JET)

  15. MDC5 - Sawtooth control for NTMs suppression Sawtooth tailoring by ECCD (AUG) • Experiments with slow Bt-ramp, 0.8 MW co-ECCD and 5.1 MW NBI: • increase of sawtooth period for deposition outside inversion radius • decrease of sawtooth period for deposition inside inversion radius • Ctr-ECCD shows inverse behaviour

  16. MDC5 - Sawtooth control for NTMs suppression Removal of large sawteeth avoids NTM (AUG) Bt ramp + feedback controlled b-ramp maintain correct ECCD deposition

  17. Two antennas at 42 MHz and +90º: • Rres(H) in centre • Fast ions stabilised sawtooth Two antennas at 47 MHz and -90º : • Rres(H) ~ Rinv • ICCD sawtooth destabilisation MDC5 - Sawtooth control for NTMs suppression JET • Control of long period fast particle stabilised sawteeth, that can induce NTMs, by ICRF near sawtooth inversion radius (RINV) on JET

  18. 1E-2 COMPASS-D DIII-D JET 1E-3 br/Bt 1E-4 1E-5 0 1 2 3 4 5 6 Bt[T] MDC6 - Error field sideband effects for ITER

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