Edge Localized Modes ELMs control by Resonant Magnetic

Edge Localized Modes (ELMs) control by Resonant Magnetic Perturbations (RMPs) E. Nardon, M. Bécoulet, G. Huysmans, O. Czarny ETFP workshop, Krakow, September 2006 E. Nardon 1/17

Introduction (1/2) • ELMs are unacceptable in ITER • DIII-D suppressed the ELMs using external magnetic perturbations • n=3 perturbations • I-coils current ~3 k. A (T. Evans, EPS 2005) • Work is ongoing to install ELMs control coils in other machines (ASDEX, MAST), project for ITER (EFDA contract « ERGITER » ) • However, the physics of ELMs suppression is not yet fully understood ETFP workshop, Krakow, September 2006 E. Nardon 2/17

Introduction (2/2) • Experimental facts • ELMs suppression = resonant effect (window in q 95) • Magnetic perturbations reduce r. P|ped and j |ped • Drop in r. P|ped due to a large drop in ne ( « pump-out » ) • Theory • RMPs produce islands in the pedestal • If RMPs are vacuum-like, ergodic region • Ergodic theory: heat transport • Simulations: too large heat flux => suggests RMPs screening • Pump-out? ETFP workshop, Krakow, September 2006 E. Nardon 3/17

Outline • Coils design for ITER (ERGITER project) • Self-consistent MHD modelling - A density transport mechanism - Cases where RMPs are not vacuum-like • Large bootstrap current: amplification • Toroidal rotation: screening ETFP workshop, Krakow, September 2006 E. Nardon 4/17

Coils design for ITER ETFP workshop, Krakow, September 2006 E. Nardon 5/17

Main principles • We use the vacuum perturbations • Goal = to produce strong edge RMPs (Reference = DIII-D’s I-coils, even configuration, 3 k. A) • Constraints = - Technical feasibility (location of the coils, required current) - Core perturbations (core MHD limits) ETFP workshop, Krakow, September 2006 E. Nardon 6/17

Where to put the coils? (1/2) • Up to now, we have looked at 2 main external to the vacuum vessel options. . . - Poloidal Field (PF) coils used as supports - Windings around the 18 midplane port plug walls ETFP workshop, Krakow, September 2006 E. Nardon 7/17

Where to put the coils? (2/2) • . . . and one inside the vacuum vessel option: windings around the blanket modules ETFP workshop, Krakow, September 2006 E. Nardon 8/17

Main conclusions of the calculations • n=3 configurations seem to be the best • External to the VV designs require several hundreds k. A for the H-mode, and much more for hybrid and steady-state • The internal design requires no more than ~20 k. A, whether q 95=3, 4 or 5 (possibility of adaptation by changing the phasings) + + --- + + -+ -+ • Core perturbations should be looked at carefully: 4/3 islands typically ~6 cm wide (but screening due to toroidal rotation could improve this) ETFP workshop, Krakow, September 2006 E. Nardon 9/17

Ongoing work Last ERGITER meeting: • Thermal constraints on the internal coils are marginal => we are doing now more precise calculations • A new possibility was suggested: coils fixed on the TF coils => under study now Some room here. . . See M. Bécoulet at upcoming IAEA for more details. . . ETFP workshop, Krakow, September 2006 E. Nardon 10/17

Self-consistent MHD modelling ETFP workshop, Krakow, September 2006 E. Nardon 11/17

Tool and method • Tool JOREK code: 3 D non-linear MHD in toroidal geometry, including the X-point (G. Huysmans, PPCF 47 (2005)) • Method • I-coils => BCs: vacuum poln=3 (Bpertn=3= ( poln=3 e )) imposed at the boundary • Simulations started with vacuum poln=3 everywhere ETFP workshop, Krakow, September 2006 E. Nardon 12/17

A density transport mechanism External magnetic perturbations => steady-state n=3 structures => E B convection n=3 ne (duration=103 A 0. 2 ms) • Candidate for the pump-out • Mechanism linked to resistivity (here S-1 A/ =5. 10 -5) ETFP workshop, Krakow, September 2006 E. Nardon 13/17

A case of amplification of the RMPs (1/2) • Tearing-stable plasmas can amplify external RMPs if close to instability threshold • Scan in jbootstrap and I-coils current 3 k. A Emagn=3 1 k. A 0. 3 k. A Unstable « Too » stable 0 k. A Stable but… time (in A) ETFP workshop, Krakow, September 2006 E. Nardon 14/17

A case of amplification of the RMPs (2/2) … poln=3 develops resonant structures… …and RMPs are amplified @ t=0 2 @ t=104 A (duration=104 A 2 ms) ETFP workshop, Krakow, September 2006 0 0. 7 E. Nardon pol 1 15/17

Screening of the RMPs by toroidal rotation • v not yet in JOREK => plasma cannot rotate • External magnetic perturbations are rotated instead j n=3 (amplitude ~10%jaxis) 2 RMPs are screened @ t=0 frot=2. 6. 10 -3 A-1~26 k. Hz 0 ETFP workshop, Krakow, September 2006 @ t=104 A E. Nardon 16/17

Summary and ongoing work • Magnetic perturbations induce an E B flow (non-static 3 D equilibrium) - Candidate for the pump-out - This flow weakens with resistivity • RMPs are not always vacuum-like - Large bootstrap => amplification - Toroidal rotation of the RMPs => screening • Candidate for the low heat transport • Now: v being implemented in JOREK ETFP workshop, Krakow, September 2006 E. Nardon 17/17