Advances in Understanding of ELM Suppression by Resonant Magnetic Perturbations (RMPs) and Implications for ITER by M.R. Wade on behalf of R. Nazikian With contributions from J. De Grassie, D. Eldon, T.E. Evans, N.M. Ferraro, B.A. Grierson, R.J. Groebner, S. Haskey, J.D. King, E. Kolemen, N. Logan, G.R. McKee, O. Meneghini, R.A. Moyer, D.M. Orlov, T.H. Osborne, C. Paz-Soldan, C.C. Petty, T.L. Rhodes, W.M. Solomon, O. Schmitz, M.W. Shafer, S.P. Smith, P.B. Snyder, E.J. Strait, and M.R. Wade Presented at the 25 th IAEA Fusion Energy Conference Saint Petersburg, Russia October 13 – 18, 2014 1 R. Nazikian/IAEA-FEC/Oct. 2014
DIII-D Program Addresses ITER Research Needs and Advances Basic Understanding of ELM Suppression ELM suppression achieved New data reveals bifurcation • • with as few as 5 internal coils indicative of resonant field penetration at ELM suppression 5 coils 7 coils 11 coils Confirmed ITER decision on ELM Providing a solid physics basis for control coil maintainability extrapolation to ITER conditions 2 R. Nazikian/IAEA-FEC/Oct. 2014
DIII-D Research is Focused on Resolving Critical Issues for ELM Suppression in ITER • ELMs in ITER may deposit up to 20 MJ to the divertor ITER ELM Control Coils - Must be mitigated or suppressed • ITER design based only on vacuum modeling - Observations suggest more complex plasma response • DIII-D Research goals: - Demonstrate ELM suppression in ITER specific conditions - Develop predictive understanding for confident extrapolation to ITER 3 R. Nazikian/IAEA-FEC/Oct. 2014
Outline • Key data on ITER urgent needs – Reduced coil assessment – Helium plasmas DIII-D ELM Control Coils • Advances in fundamental understanding – Working model – Evidence for resonant field penetration • Projections to ITER and future devices – Confinement scaling when operating at threshold – Towards steady state 4 R. Nazikian/IAEA-FEC/Oct. 2014
ELM Suppression Achieved with as Few as 5 Control Coils, Affirming ITER Coil Maintainability Design Choice • Reduced coil set surprisingly led to reduced power requirement • n=1 sideband correction essential for avoiding locked modes Orlov EX/P2-21 5 R. Nazikian/IAEA-FEC/Oct. 2014
RMP ELM suppression in Low Power, Low Torque Helium Plasmas Meets Requirements for ITER Non-Nuclear Phase • ELM suppression in dominant Helium plasma – n He /n i > 80 % • Obtained in conditions expected in ITER non-nuclear phase – Input power just above L-H threshold (P EC =3.0 MW) – Low NBI torque (T inj ≈ 0.1 N -m) • Extension to higher power, high performance plasmas remains 6 R. Nazikian/IAEA-FEC/Oct. 2014
Outline • Key data on ITER urgent needs – Reduced coil assessment – Helium plasmas • Advances in fundamental understanding – Working model – Evidence for resonant field penetration • Projections to ITER and future devices – Confinement scaling when operating at threshold – Towards steady state 7 R. Nazikian/IAEA-FEC/Oct. 2014
Model: Enhanced Local Transport Limits Pedestal Expansion, Preventing Peeling Mode Onset • EPED: Pedestal expansion governed by KBM-driven Pedestal Pressure (kPa) transport until peeling- ballooning stability exceeded Pedestal Width ( N ) KBM = Kinetic Ballooning Mode Snyder, TH/2-2 8 R. Nazikian/IAEA-FEC/Oct. 2014
Model: Enhanced Local Transport Limits Pedestal Expansion, Preventing Peeling Mode Onset • EPED: Pedestal expansion governed by KBM-driven Pedestal Pressure (kPa) transport until peeling- ballooning stability exceeded • Model of suppression: RMP RMP- induces enhanced transport at Induced the top of pedestal transport • Enhanced transport keeps pedestal from expanding to Pedestal Width ( N ) unstable width Transport at top of pedestal is key KBM = Kinetic Ballooning Mode Snyder, TH/2-2 9 R. Nazikian/IAEA-FEC/Oct. 2014
Leading Mechanism for ELM Suppression Based on Resonant Field Penetration at the Top of the Pedestal • IAEA 2012: ELM suppression occurs when co-alignment of: – Rational surface(s) with same pitch as high-amplitude poloidal harmonic of applied field – Region of w ⊥ ,e = w ExB + w e,dia ≈ 0 – Top of the pedestal Leads to island formation at top of pedestal, arresting pedestal expansion • Evidence for n=3 islands lacking due to small island size and spectral variation limitations 10 R. Nazikian/IAEA-FEC/Oct. 2014
Plasma Response to 3D Field Explored by Continuous Variation of n=2 Poloidal Spectrum rotating • Vary relative phase between upper & lower rows to continuously modify poloidal spectrum Df UL Df UL = relative phase of upper and static lower I-coils • New magnetic sensors and improved profile measurements resolve plasma response to Df UL Vacuum 11 R. Nazikian/IAEA-FEC/Oct. 2014
MARS-F Simulation Predicts Ideal-MHD Response Varies Dramatically as Df UL is Varied Plasma • MARS-F shows strong Response modulation of edge tearing drive with Df UL • Amplification also seen Vacuum relative to vacuum 12 R. Nazikian/IAEA-FEC/Oct. 2014
Minimum Pedestal Density and ELM Suppression Not Aligned with Peak of Vacuum Coupling ELM Suppression Minimum density and ELM • suppression occurs at Df UL ≈30 deg. – Vacuum resonance peaks at Df UL ≈ 90 deg. Brief periods of ELM suppression • occur at same Df UL at minimum density – ITER Similar Shape, q 95 =4.1 13 R. Nazikian/IAEA-FEC/Oct. 2014
IPEC Simulations Indicate Density Response, Suppression Aligned with Maximum Tearing Drive • IPEC calculates ideal MHD coupling to low order surfaces – Tearing drive Tearing Drive • Maximum density response and suppression observed at different Df UL from vacuum alignment • Resonant field penetration is most likely to occur at the peak of the tearing drive Paz-Soldan, EX/P2-28 14 R. Nazikian/IAEA-FEC/Oct. 2014
Dominant Resonant Response to n=2 RMP is Edge Localized, Does Not Possess Ballooning Structure Edge resonant response – strong Global kink response – weak • • coupling to edge coupling to edge Similar to MAST modeling* showing density response correlated with edge resonant coupling *Y. Liu et al ., Nucl. Fusion 51 (2011) 083002 Paz-Soldan, EX/P2-28 15 R. Nazikian/IAEA-FEC/Oct. 2014
Bifurcations to ELM Suppression Observed at the Peak of the Calculated Tearing Drive • At peak predicted tearing drive ( Df UL =30 o ), rapid bifurcation occurs • Exhibits signatures of field penetration/island formation – Rapid edge spin-up – Flattening at pedestal top – Proximity to low order q=m/n • Suppression correlated with increase on high-field-side (HFS) magnetics – Weak response on low-field-side T.E. Evans EX/1-3 16 R. Nazikian/IAEA-FEC/Oct. 2014
M3D-C1 Simulation Confirms Strong Resonant Field Penetration at Top of Pedestal During ELM Suppression • T e pedestal width narrows, gradient decreases at top of pedestal • |V ⊥ e | strongly decrease at q=4 in suppression window due to – V f spin-up – Temperature flattening • M3D-C1 linear single fluid MHD simulation predicts strong M3D-C1 penetration at the q=4 surface – Localized near V ⊥ e ≈0 – Predicts HFS B pol increase 17 R. Nazikian/IAEA-FEC/Oct. 2014
Pedestal Dynamics with Static n=2 RMP Indicates Critical Threshold for Penetration and Screening Static n=2 RMP at Df UL =0, • ELM Suppressed constant parameters – Near peak tearing drive Back Transition to Std. ELM-free Bifurcations observed • near ELM suppression threshold – V ⊥ e , T e , HFS magnetics Back transitions to standard • ELM-free before ELMs Te (keV) Future: Understand threshold • dynamics to predict requirements ELM Suppressed for future experiments Standard ELM Free 18 R. Nazikian/IAEA-FEC/Oct. 2014
Pedestal Turbulence Also Changes Dramatically, Consistent with Resonant Field Penetration (a.u.) ELM Suppressed Back Transition to Standard ELM Free Consistent with theory that resonant • field penetration suppresses zonal flow and increases turbulence – Leconte, P.H. Diamond, Phys. Plasmas (2011) Z. Lin TH/7-2 19 R. Nazikian/IAEA-FEC/Oct. 2014
Outline • Key data on ITER urgent needs – Reduced coil assessment – Helium plasmas Pedestal Pressure (kPa) • Advances in fundamental understanding – Working model – Evidence for resonant RMP- field penetration Induced transport • Projections to ITER and future devices – Confinement scaling Pedestal Width ( N ) when operating at threshold – Towards steady state 20 R. Nazikian/IAEA-FEC/Oct. 2014
Pedestal Model (EPED) Accurately Predicts Pedestal Pressure at the Threshold of ELM Suppression Pedestal pressure at or • above EPED prediction in ELM mitigated and no RMP plasmas ELM suppressed plasmas • within 10% of EPED prediction at threshold How is global • confinement affected by RMP? 21 R. Nazikian/IAEA-FEC/Oct. 2014
Global Confinement and H-factor Are Not Substantially Affected at the Threshold of ELM Suppression 10% degradation of H- • factor at threshold of ELM suppression Overdriving suppression • can further degrade confinement Density and I-coil • feedback control needed to maintain high confinement Kolemen, PPC/1-1 Hawryluk, PPC/P2-33 22 R. Nazikian/IAEA-FEC/Oct. 2014
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