(EX/9-3) Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes

R.A. Moyer1), K.H. Burrell2), T.E. Evans2), M.E. Fenstermacher3), P. Gohil2), I. Joseph1), T.H. Osborne2), M.J. Schaffer2), P.B. Snyder2), J.G. Watkins4), L.R. Baylor5), M. Bécoulet6), J.A. Boedo1), N.H. Brooks2), E.J. Doyle7), K.-H. Finken8), P. Garbet6), M. Groth3), J. Harris5), E.M. Hollmann1), G.L. Jackson2), M. Jakubowski8), T.C. Jernigan5), S. Kasilov9), C.J. Lasnier3), A.W. Leonard2), M. Lehnen8), J. Lönnroth10), E. Nardon6), V. Parail11), G.D. Porter3), T.L. Rhodes7), D.L. Rudakov1), A. Runov12), O. Schmitz8), R. Schneider12), D.M. Thomas2), P. Thomas6), G. Wang7), W.P. West2), L. Yan13), J.H. Yu1), L. Zeng7)
 
1) University of California-San Diego, La Jolla, California, United States of America
2) General Atomics, San Diego, California, United States of America
3) Lawrence Livermore National Laboratory, Livermore, California, United States of America
4) Sandia National Laboratories, Albuquerque, New Mexico, United States of America
5) Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
6) Association EURATOM-CEA, Cadarache, France
7) University of California-Los Angeles, Los Angeles, California, United States of America
8) Forschungszentrum Julich, Association EURATOM-FZJ, Trilateral Euregio Cluster, Germany
9) Kharkov Institute for Physics and Technology, Kharkov, Ukraine
10) Association EURATOM-Tekes, Helsinki University of Technology, Finland
11) EURATOM/UKAEA Fusion Association, Culham Science Center, United Kingdom
12) Max Planck Institute, Greifswald, Germany
13) Southwest Institute for Physics, Chengdu, China

Abstract.  Edge localized mode (ELM) control is a critical issue for ITER because the impulsive heat load from ELMs is predicted to erode the divertor target plates and limit the divertor lifetime. In DIII-D, edge resonant magnetic perturbations (RMPs) with n=3 toroidal symmetry have been used to eliminate large Type I ELMs without degrading confinement at pedestal collisionalities of 0.2, typical of those expected for ITER. ELMs are completely eliminated during the RMP pulse provided the edge safety factor is near the resonant condition q95∼3.7. The RMPs enhance the radial transport across the H mode pedestal, reducing the pressure gradient enough to stabilize the MHD modes that trigger ELMs. The reduction is controlled by changing the RMP amplitude. Linear peeling-ballooning stability analysis with the ELITE code confirms that the ELMs are suppressed by reducing the pressure gradient below the peeling-ballooning limit in all cases analyzed to date. Surprisingly, the pressure gradient reduction results primarily from an increase in particle transport, not electron thermal transport, a result that is inconsistent with stochastic layer transport theory. There is no edge harmonic oscillation (seen in QH modes) or intermittent transport (seen in higher collisionality ELMing discharges) during the ELM-suppressed phase. Instead, pedestal density fluctuations increase, consistent with enhanced anomalous transport replacing the impulsive ELM transport and maintaining steady state H-mode. In ELM control experiments with collisionalities of 4, large ELMs are replaced by small recycling fluctuations, possibly Type II ELMs, that are correlated with increased intermittent transport. The increased intermittency yields a similar level of transport, leaves the pressure gradient unchanged near the peeling-ballooning boundary, and reduces the heat impulses to the divertor. Together, these results suggest that optimization of the ELM suppression might be possible. These results will be extended to ITER-relevant pedestal rotation and triangularity using the new balanced neutral beam injection and high triangularity divertor pumping capabilities and will help assess the viability of using edge RMPs to control ELMs in ITER.
* Work supported by US DOE under DE-FG02-04ER54758, DE-FC02-04ER54698, DE-FG03-01ER54615, W-7405-ENG-48, DE-FG03-96ER54373, and DE-AC04-94AL85000.

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