Evans-ELMs by xiangpeng


									 Edge Localized Mode and pedestal control
 using resonant magnetic perturbations                                 T. E. Evans
• Transient heat flux excursions are a critical ITER issue: ITER 2007-20162037
    –   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
                                                                       DEMO 2024-2036
•   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

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

Supporting material

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.
The predicted tangle forms non-axisymmetric magnetic
footprints which have been experimentally observed

    123300: filtered CIII Xpt-TV

    123301: filtered D Xpt-TV

•   Te reflects a superposition of both upper invariant manifolds
•   Multiple footprint stripes observed during I-coil RPM operation

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

                             QuickTime™ and a
                       are need ed to see this picture.

             I. Joseph, et al., Nucl. Fusion, (2007) to be submitted.
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
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.
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.
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.
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)
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)
Calculations of the stochastic layer width are
sensitive to plasma current and pressure profiles

                 Spectral gap
               Spectral gap

     Island width

•   Fast ion pressure (measured) and edge bootstrap current distribution (modeled) are needed for
    accurate calculations of the stochastic layer width.

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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