Magnetic Perturbations (RMPs) and Implications for ITER by M.R. - - PowerPoint PPT Presentation

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Magnetic Perturbations (RMPs) and Implications for ITER by M.R. - - PowerPoint PPT Presentation

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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,

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Advances in Understanding of ELM Suppression by Resonant Magnetic Perturbations (RMPs) and Implications for ITER

by

M.R. Wade

  • n 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

25th IAEA Fusion Energy Conference Saint Petersburg, Russia October 13–18, 2014

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DIII-D Program Addresses ITER Research Needs and Advances Basic Understanding of ELM Suppression

  • ELM suppression achieved

with as few as 5 internal coils

  • New data reveals bifurcation

indicative of resonant field penetration at ELM suppression

5 coils 7 coils 11 coils

 Confirmed ITER decision on ELM

control coil maintainability

 Providing a solid physics basis for

extrapolation to ITER conditions

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DIII-D Research is Focused on Resolving Critical Issues for ELM Suppression in ITER

ITER ELM Control Coils

  • ELMs in ITER may deposit up to 20 MJ

to the divertor

  • 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

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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

DIII-D ELM Control Coils

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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

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RMP ELM suppression in Low Power, Low Torque Helium Plasmas Meets Requirements for ITER Non-Nuclear Phase

  • ELM suppression in dominant

Helium plasma

– nHe/ni > 80 %

  • Obtained in conditions expected

in ITER non-nuclear phase

– Input power just above L-H

threshold (PEC=3.0 MW)

– Low NBI torque (Tinj ≈ 0.1 N-m)

  • Extension to higher power, high

performance plasmas remains

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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

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  • EPED: Pedestal expansion

governed by KBM-driven transport until peeling- ballooning stability exceeded

Model: Enhanced Local Transport Limits Pedestal Expansion, Preventing Peeling Mode Onset

Pedestal Width (N) Pedestal Pressure (kPa)

Snyder, TH/2-2

KBM = Kinetic Ballooning Mode

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  • EPED: Pedestal expansion

governed by KBM-driven transport until peeling- ballooning stability exceeded

  • Model of suppression: RMP

induces enhanced transport at the top of pedestal

  • Enhanced transport keeps

pedestal from expanding to unstable width

Transport at top of pedestal is key

Model: Enhanced Local Transport Limits Pedestal Expansion, Preventing Peeling Mode Onset

RMP- Induced transport

Pedestal Width (N) Pedestal Pressure (kPa)

Snyder, TH/2-2

KBM = Kinetic Ballooning Mode

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Leading Mechanism for ELM Suppression Based on Resonant Field Penetration at the Top of the Pedestal

  • IAEA 2012: ELM suppression
  • ccurs when co-alignment of:

– Rational surface(s) with same pitch as high-amplitude poloidal harmonic of applied field – Region of w⊥,e = wExB + we,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

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Plasma Response to 3D Field Explored by Continuous Variation of n=2 Poloidal Spectrum

  • Vary relative phase between upper &

lower rows to continuously modify poloidal spectrum

฀ DfUL = relative phase of upper and lower I-coils

  • New magnetic sensors and improved

profile measurements resolve plasma response to DfUL

static rotating

DfUL

Vacuum

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MARS-F Simulation Predicts Ideal-MHD Response Varies Dramatically as DfUL is Varied

  • MARS-F shows strong

modulation of edge tearing drive with DfUL

  • Amplification also seen

relative to vacuum

Vacuum Plasma Response

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Minimum Pedestal Density and ELM Suppression Not Aligned with Peak of Vacuum Coupling

  • Minimum density and ELM

suppression occurs at DfUL≈30 deg.

– Vacuum resonance peaks at DfUL≈90 deg.

  • Brief periods of ELM suppression
  • ccur at same DfUL at minimum

density

– ITER Similar Shape, q95=4.1 ELM Suppression

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IPEC Simulations Indicate Density Response, Suppression Aligned with Maximum Tearing Drive

  • IPEC calculates ideal MHD

coupling to low order surfaces

– Tearing drive

  • Maximum density response and

suppression observed at different DfUL from vacuum alignment

  • Resonant field penetration is most

likely to occur at the peak of the tearing drive Paz-Soldan, EX/P2-28 Tearing Drive

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Dominant Resonant Response to n=2 RMP is Edge Localized, Does Not Possess Ballooning Structure

Paz-Soldan, EX/P2-28

  • Edge resonant response – strong

coupling to edge

  • Global kink response – weak

coupling to edge

Similar to MAST modeling* showing density response correlated with edge resonant coupling

*Y. Liu et al., Nucl. Fusion 51 (2011) 083002

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Bifurcations to ELM Suppression Observed at the Peak of the Calculated Tearing Drive

  • At peak predicted tearing drive

(DfUL=30o), 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
  • n high-field-side (HFS) magnetics

– Weak response on low-field-side T.E. Evans EX/1-3

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M3D-C1 Simulation Confirms Strong Resonant Field Penetration at Top of Pedestal During ELM Suppression

  • Te pedestal width narrows,

gradient decreases at top of pedestal

  • |V⊥e| strongly decrease at q=4

in suppression window due to

– Vf spin-up – Temperature flattening

  • M3D-C1 linear single fluid MHD

simulation predicts strong penetration at the q=4 surface – Localized near V⊥e≈0 – Predicts HFS Bpol increase

M3D-C1

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Pedestal Dynamics with Static n=2 RMP Indicates Critical Threshold for Penetration and Screening

  • Static n=2 RMP at DfUL=0,

constant parameters

– Near peak tearing drive

  • Bifurcations observed

near ELM suppression threshold

– V⊥e , Te , HFS magnetics

  • Back transitions to standard

ELM-free before ELMs

  • Future: Understand threshold

dynamics to predict requirements for future experiments

ELM Suppressed Standard ELM Free

Te (keV)

ELM Suppressed Back Transition to Std. ELM-free

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Pedestal Turbulence Also Changes Dramatically, Consistent with Resonant Field Penetration

  • Z. Lin TH/7-2
  • Consistent with theory that resonant

field penetration suppresses zonal flow and increases turbulence

– Leconte, P.H. Diamond, Phys. Plasmas (2011) ELM Suppressed Back Transition to Standard ELM Free

(a.u.)

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Outline

RMP- Induced transport

Pedestal Width (N) Pedestal Pressure (kPa)

  • 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

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  • R. Nazikian/IAEA-FEC/Oct. 2014

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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?

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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

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Future Directions: Progress Towards Steady State Hybrid Regime with ELM Suppression

  • Strong ELM mitigation obtained

in fully noninductive plasmas

฀ bN = 3, H98 = 1.35, q95= 6.5

  • Higher RMP amplitude led to

full ELM suppression… but

  • verdriven

Next Step: ELM suppression in fully noninductive plasmas

Clamped

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  • DIII-D responds to ITER research needs, demonstrates

 ELM suppression with reduced coil set, dominant He plasmas

  • New studies validate leading model of ELM suppression

 Bifurcation driven by resonant field penetration at top of pedestal

  • Confinement in RMP ELM suppressed plasmas compatible with ITER

performance requirements Future Directions:

  • Develop predictive understanding of bifurcation dynamics
  • Develop steady-state ELM suppressed regimes for next step devices

DIII-D Has Addressed Immediate ITER Physics Needs and Advanced Understanding of ELM Suppression