(IT/1-3) Edge pedestal physics and its implications for ITER

Y. Kamada1), A. W. Leonard2), G. Bateman3), M. Becoulet4), C. S. Chang5), T. Eich6), T. E. Evans2), R. J. Groebner2), P. N. Guzdar7), L. D. Horton6), A. Hubbard8), J. W. Hughes8), K. Ida9), G. Janeschitz10), K. Kamiya1), A. Kirk11), A. H. Kritz3), A. Loarte12), J. S. Lonnroth11), C. F. Maggi6), R. Maingi13), H. Meyer11), V. Mukhovatov14), T. Onjun15), M. Osipenko16), T. H. Osborne2), N. Oyama1), G. W. Pacher17), H. D. Pacher18), A. Y. Pankin3), V. Parail11), A. R. Polevoi14), T. Rognlien19), G. Saibene12), R. Sartori12), M. Shimada14), P. B. Snyder2), M. Sugihara14), W. Suttrop6), H. Urano1), M. R. Wade2), H. R. Wilson20), X. Q. Xu19), M. Yoshida1), ITPA Edge & Pedestal Physics Topical Group
1) Japan Atomic Energy Agency, Naka, Ibaraki, Japan
2) General Atomics,
3) Lehigh Univ.
4) Association Euratom-CEA
5) New York Univ.
6) Association Euratom-IPP
7)Univ. Maryland
8) MIT Science and Fusion Center
9) National Institute for Fusion Science
10) FZK-PL-Fusion
11) Association Euratom-UKAEA
13) Oak Ridge National Laboratory
14) ITER International Team
15 ) Thammasart Univ.
16) Kurchatov Institute
17) Hydro-Quebec
18) INRS
19 )Lawrence Livermore National Laboratory
20) Univ. of York

Abstract.  The H-mode pedestal plays a central role in achieving the required integrated plasma performance in ITER. The critical issues in the pedestal research are 1) understanding of the type I ELM trigger and energy losses, 2) identification of the processes determining the pedestal structure, 3) development of small/no ELM regimes and type I ELM mitigation methods, and 4) construction of integrated prediction codes. For all of these issues, remarkable progress has been achieved by integrating the results obtained in single- and inter-machine experiments (Alcator C-Mod, ASDEX-U, DIII-D, JET, JFT-2M, JT-60U, MAST and NSTX) with theoretical progress. It has been confirmed that the trigger of type-I ELM can be explained systematically by the peeling-ballooning modes. Nonlinear explosive evolution of ELM crash has been revealed by improved diagnostics and reproduced numerically. The ratio of the energy loss by an ELM to the pedestal stored energy increases with decreasing collisionality, and a simple projection to ITER shows that it exceeds the allowable level. It has been revealed that the transport between ELMs is close to the ion neoclassical transport and that the pedestal width is determined by the magnetic field structure and non-dimensional parameters. Neutral penetration depth also plays a role. Prediction of the fusion gain Q in ITER depends strongly on the pedestal temperature Tped. Although some models predict a Tped∼4 keV with Q > 10, the range of predicted Tped is still wide. The ripple loss of fast ions and the shift of plasma rotation into co-direction increase the pedestal height. The small/no-ELM regimes (QH, grassy-ELM, type II ELM, EDA/HRS) have been reproduced in multiple devices by matching the non-dimensional parameters and the plasma shape. Accessibility to these regimes has been categorized. The grassy-ELM and QH regimes have been achieved at collisionalities close to ITER. Type I ELM mitigation techniques, such as pellet injection and application of a resonant magnetic perturbation, have been developed and their applicability to ITER is under evaluation. The modeling capability for integrating the core, pedestal, SOL and divertor regions has achieved remarkable progress. Models based on turbulence suppression and peeling-ballooning stability have reproduced experiments and predicted ELMing edge evolution in ITER.

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