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Toroidally resolved measurements of ELMs in RMP and non-RMP H-mode discharges on DIII-D M.W. Jakubowski 1, T.E. Evans 3, C.J. Lasnier 4, O. Schmitz 2, M.E. Fenstermacher 4, R. Laengner 2, R.C. Wolf 1, L.B. Baylor 3, J.A. Boedo 5, K.H. Burrell 3, J.S. deGrassie 3, P. Gohil 3, R.A. Moyer 5, A.W. Leonard 3, C.C. Petty 3, R.I. Pinsker 3, T.L. Rhodes 5, M.J. Schaffer 3, P.B. Snyder 3, H. Stoschus 2, T. Osborne 3, D. Orlov 5, E. Unterberg 3, J.G. Watkins 6 1 Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Greifswald, Germany 2 Forschungszentrum Jülich, IEF-4, Association FZJ-EURATOM, TEC, Jülich, Germany 3 General Atomics, P.O. Box 85608, San Diego, California, 92186-5608 U.S.A. 4 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550, U.S.A. 5 University of California, San Diego, La Jolla, CA 92093, U.S.A. 6 Sandia National Laboratory, Albuquerque, New Mexico, U.S.A. M.W. Jakubowski, et al., PSI San Diego (2010)

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Outlook Motivation Experimental set-up with two toroidally separated infra-red cameras Evolution of ELM behavior from non-RMP to mitigated RMP scenario.

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Motivation The common picture of ELMs is that they are filamentary structures creating toroidally symmetric heat loads, when averaged over time. How does it change with RMP? On DIII-D application of n=3 resonant magnetic perturbation fields (RMP) allows to achieve H-mode with ELMs suppressed or mitigated. What can we say about heat loads due to mitigated ELMs? As ELMs prevent accumulation of impurities inside the plasma volume a scenario with very small, well controlled ELMs would be beneficial for ITER.

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In RMP: once H98 comes back to pre-RMP value very small ELMs appear 1 2 3 4 We have realized four discharges with different q 95 : 3.5, 3.9, 4.1, 4.3. Four different phases of the discharge.

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Wetted area increases linearly with ELM size in H- mode discharges Wetted area is defined as: M.W. Jakubowski et al., Nuclear Fusion 49 (2009) 095013

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Slope in non-RMP H-mode is a function of plasma current Wetted area is defined as: M.W. Jakubowski et al., Nuclear Fusion 49 (2009) 095013 Slope of w f = f(E dep ) changes with plasma current A = tan

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Without RMP evolution of ELM structures shows 3D dynamics Evolution and structure of heat flux density distribution on the surface of lower divertor can be very different (bottom graphs), but there are cases, where the evolution is rather similar (top example). Energy deposited per ELM is defined as: With toroidal symmetries defined as: = 160° = 55° = 160° = 55° smaller ELM larger ELM M.W. Jakubowski, et al., PSI San Diego (2010)

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With RMP heat deposition patterns follow structure of stochastic boundary Introducing RMP (5 kA, q 95 = 3.5) changes evolution of type-I ELMs to small events following topology of the stochastic boundary. Smaller ELMs “fill” two lobes of striated footprints Larger ELMs expel enough energy to “fill” the third lobe (bottom graph). = 160° = 55° = 160° = 55° smaller ELM larger ELM M.W. Jakubowski, et al., PSI San Diego (2010)

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Without RMP larger variability of deposited energy and wetted area between toroidal locations Application of RMP reduces significantly ELM energies. Higher heating power (9 MW) results in stronger ELM mitigation. Without RMP some ELMs show toroidal asymmetries up to 50% on average there is no toroidal asymmetry (R E ) between energy deposited on two toroidal locations Without RMP there is also rather strong variability of wetted area (R w ) between two locations. Introducing RMP reduces variability of deposited energy and wetted area, but creates small asymmetries in deposited.

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On average no toroidal asymmetry without RMP Without RMP (blue curves): average ELM energy almost does not change with q 95 with variability of deposited energy of about 50%. on average no toroidal asymmetry in deposited energy and slight asymmetry in wetted area. deposited energy [kJ] symmetry of w f - R w symmetry of E dep - R E M.W. Jakubowski, et al., PSI San Diego (2010)

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RMP at q 95 closer to resonant window reduces ELM energies and variability. Without RMP (blue curves): average ELM energy almost does not change with q 95 with variability of deposited energy of about 50%. wetted area change rate increases linearly with q 95 on average no toroidal asymmetry. RMP at P tot = 6 MW (red curves): reduces average energy by factor of 2 toroidal asymmetry depends on q 95 deposited energy [kJ] symmetry of w f - R w symmetry of E dep - R E M.W. Jakubowski, et al., PSI San Diego (2010)

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Higher P tot enhances coupling of RMP with plasma: smaller ELMs and toroidal asymmetries. Without RMP (blue curves): average ELM energy almost does not change with q 95 with variability of deposited energy of about 50%. wetted area change rate increases linearly with q 95 on average no toroidal asymmetry. RMP at P tot = 5 MW (red curves): reduces average energy by factor of 2 toroidal asymmetry depends on q 95 RMP at P tot = 9 MW (green curves): reduces ELM energy even better (8 kJ 3 kJ) toroidal asymmetries are slightly higher deposited energy [kJ] symmetry of w f - R w symmetry of E dep - R E M.W. Jakubowski, et al., PSI San Diego (2010)

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Without RMP ELMs spanned over wide spectrum of energies. Without RMP one observes rather wide spectrum of ELMs (up to 20 kJ). Shape of the population distribution does not depend on q 95 M.W. Jakubowski, et al., PSI San Diego (2010)

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Population curve of ELMs has two subgroups different ELMs? Introducing RMP at 6 MW heating power suppresses large ELMs. In case of q95 = 3.5 almost 90% of ELMs are below 3 kJ. M.W. Jakubowski, et al., PSI San Diego (2010)

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At P tot = 9 MW and q 95 = 3.5 virtually all ELMs below ITER limit. At higher power coupling of RMP with plasma is better Strong dependence of population distribution on q 95 In the case of q95 = 3.9 virtually all ELMs deposit less than 3 kJ). M.W. Jakubowski, et al., PSI San Diego (2010)

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Amplitude and frequency is very sensitive to q 95 T. Evans, et al., IAEA, Geneve (2008) M.W. Jakubowski, et al., PSI San Diego (2010)

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Summary On average in DIII-D H-mode plasmas without RMP type-I ELMs do not introduce toroidal asymmetries in energy deposition. However, individual events show up to 50% toroidal asymmetries in deposited energy to the divertor and rather different evolution of heat flux density patterns. The wetted area increases linear with ELM size. Slope is a function of plasma current. Applying RMP at proper q 95 significantly reduces energy deposited per ELM keeping virtually all events below certain level, which is compatible with ITER guidelines. Their structure of deposition patterns follows 3D topology of stochastic boundary, which also results in small toroidal asymmetries. RMP allowed to realize a scenario with very small, well controlled ELMs. M.W. Jakubowski, et al., PSI San Diego (2010)

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ELMs in RMP phase follow stochastic boundary M.W. Jakubowski et al., NF 49 (2009) 095013 M.W. Jakubowski, et al., PSI San Diego (2010)

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Weak effect of RMP in the initial phase In the initial RMP phase most of the ELMs deposit energy between 2 and 6 kJ Rather weak effect of RMP on ELM behavior Shape of the population curve does not depend on q 95 M.W. Jakubowski, et al., PSI San Diego (2010)

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Change of heat flux density M.W. Jakubowski, et al., PSI San Diego (2010)

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