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Edge Localized Mode and pedestal control using resonant magnetic perturbations

Edge Localized Mode and pedestal control using resonant magnetic perturbations. T. E. Evans. ITER 2007- 2016  2037. Transient heat flux excursions are a critical ITER issue: Transient energy impulses to material surface must be < 45-60 MJm -2 s -1/2 (ideal ablation limit)

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Edge Localized Mode and pedestal control using resonant magnetic perturbations

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  1. Edge Localized Mode and pedestal control using resonant magnetic perturbations T. E. Evans ITER 2007-20162037 • Transient heat flux excursions are a critical ITER issue: • Transient energy impulses to material surface must be < 45-60 MJm-2s-1/2 (ideal ablation limit) • Implies transients (ELMs ~0.5 ms) < 6-8 MJ (assuming in-out and axisymmetric target distribution) • Scaling from present tokamaks~12-20 MJ • In DEMO transients heat flux excursions are expected to be at least 5X large than in ITER • A reliable ELM control system is essential for DEMO • Resonant Magnet Perturbations (RMPs): • Produce complete ELM elimination • at reactor relevant collisionalities • with robust edge transport barriers and • somewhat improved Teped • Appear to be scalable to reactor plasmas • Provide pedestal and steady-state heat flux control that may lead to improved H-mode performance DEMO 2024-2036

  2. RMP ELM control in DEMO requires developing scalable physics models and optimized coil designs • Current RMP experiments are providing valuable basic physics data: • Current physics understanding large pedestal resonances with minimal core resonances and non-resonant components • Currently restricted to suboptimal coils (using field-error correction and RWM control coils) • ITER attempting to shoehorn RMP ELM control coils into its design but facing: • Rigid constraints on coil design parameters • Suboptimal design, reduced spectral flexibility • No provisions for mid-course coil optimization • The program is facing a significant gap in the development of RMP ELM control for DEMO that will not be filled by ITER • This gap could be filled with a dedicated new device or a significant upgrade (~100M$) of an existing device • Optimized RMP coil design tightly integrated into device design • Options for mid-course coil and divertor changes based on developing physics understanding ( strongly integrated theory, modeling and experiments) • New physics understanding  potential for improved DEMO performance

  3. Supporting material

  4. ELMs are completely eliminated with RMPs in high confinement plasmas with ITER Similar Shapes • 2006 lower divertor reconfiguration allows collisionality control (pumping) in ITER Similar Shape T.E. Evans, et al., Nature Physics, 2 (2006) 419.

  5. The predicted tangle forms non-axisymmetric magnetic footprints which have been experimentally observed 123300: filtered CIII Xpt-TV • Te reflects a superposition of both upper invariant manifolds • Multiple footprint stripes observed during I-coil RPM operation 123301: filtered D Xpt-TV I. Joseph, et al., Nucl. Fusion, (2007) to be submitted.

  6. 3D structure of tangle is seen by rotating the magnetic perturbation toroidally I. Joseph, et al., Nucl. Fusion, (2007) to be submitted.

  7. The peak divertor heat flux is reduced by 40% due to separatrix splitting when the RMP is applied • Split heat flux peaks are consistent with divertor plate homoclinic tangle intersections T.E. Evans, et al., J. Physics: Conf. Ser., 7 (2005) 174

  8. Installation of magnetic coils on MAST Plan to install 12 “DIII-D I-coil” in MAST To be used for ELM mitigation and TAE studies Complete installation by the end of 2007 A. Kirk, et al., 3rd Stochasticity in Fusion Plasmas (2007), Juelich, Germany.

  9. Proposed RMP coil design for ASDEX-U • Both n=3 and n=4 RMP ELM control experiments will be possible W. Suttrop, et al., 3rd Stochasticity in Fusion Plasmas (2007), Juelich, Germany.

  10. Several RMPs coil design options are being studied for ELM and heat flux control on ITER • Both internal (n=3 and n=4) and external (n=3) RMP ELM and divertor heat flux cotrol coil design are being modeled for ITER M. Becoulét, et al., Nucl. Fusion (2007) submitted.

  11. RMP H-modes have reduced particle confinement times compared to ELMing H-modes • Three small ELM-like D bursts are triggered during the HFS pellet ablation phase but do not persist. T.E. Evans, et al., Nucl. Fusion (submitted June, 2007)

  12. RMP ELM suppression is correlated with a narrowing and shifting of the pedestal gradient profile T.E. Evans, et al., Nucl. Fusion (submitted June, 2007)

  13. Spectral gap Island width Spectral gap Calculations of the stochastic layer width are sensitive to plasma current and pressure profiles • Fast ion pressure (measured) and edge bootstrap current distribution (modeled) are needed for accurate calculations of the stochastic layer width.

  14. RMP induced edge transport barriers have been observed in limiter tokamaks Confirmed in TEXTOR: K. H. Finken, et al., Phys. Rev. Lett. 98 (2007) 065001 T.E. Evans, et al., J. Nucl. Mater. 196-198 (1992) 421

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