Toroidally resolved measurements of ELMs in RMP and non-RMP H-mode discharges on DIII-D

1. Toroidally resolved measurements of ELMs in RMP and non-RMP H-mode discharges on DIII-D M.W. Jakubowski1, T.E. Evans3, C.J. Lasnier4, O. Schmitz2, M.E. Fenstermacher4, R. Laengner2, R.C. Wolf1, L.B. Baylor3, J.A. Boedo5, K.H. Burrell3, J.S. deGrassie3, P. Gohil3, R.A. Moyer5, A.W. Leonard3, C.C. Petty3, R.I. Pinsker3, T.L. Rhodes5,M.J. Schaffer3, P.B. Snyder3, H. Stoschus2, T. Osborne3, D. Orlov5, E. Unterberg3, J.G. Watkins6 1 Max-Planck-InstitutfürPlasmaphysik, IPP-EURATOM Association, Greifswald, Germany2 ForschungszentrumJülich, IEF-4, Association FZJ-EURATOM, TEC, Jülich, Germany3 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)

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

3. 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.

4. In RMP: once H98 comes back to pre-RMP value very small ELMs appear 1 3 2 4 • We have realized four discharges with different q95: 3.5, 3.9, 4.1, 4.3. • Four different phases of the discharge.

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

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

7. 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: j = 160° j = 55° smaller ELM j = 160° j = 55° larger ELM M.W. Jakubowski, et al., PSI San Diego (2010)

8. With RMP heat deposition patterns follow structure of stochastic boundary • Introducing RMP (5 kA, q95 = 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). j = 160° j = 55° smaller ELM j = 160° j = 55° larger ELM M.W. Jakubowski, et al., PSI San Diego (2010)

9. Without RMP larger variability of deposited energy and wetted area between toroidal locations • Application of RMPreducessignificantlyELMenergies. 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 (RE) between energy deposited on two toroidal locations • Without RMP there is also rather strong variabilityof wetted area (Rw) between two locations. • Introducing RMP reduces variability of deposited energy and wetted area, but creates small asymmetries in deposited.

10. On average no toroidal asymmetry without RMP deposited energy [kJ] • Without RMP (blue curves): • average ELM energy almost does not change with q95 with variability of deposited energy of about 50%. • on average no toroidal asymmetry in deposited energyand slight asymmetry in wetted area. symmetry of wf - Rw symmetry of Edep - RE M.W. Jakubowski, et al., PSI San Diego (2010)

11. RMP at q95 closer to resonant window reduces ELM energies and variability. deposited energy [kJ] • Without RMP (blue curves): • average ELM energy almost does not change with q95 with variability of deposited energy of about 50%. • wetted area change rate increases linearly with q95 • on average no toroidal asymmetry. • RMP at Ptot = 6 MW (red curves): • reduces average energy by factor of 2 • toroidal asymmetry depends on q95 symmetry of wf - Rw symmetry of Edep - RE M.W. Jakubowski, et al., PSI San Diego (2010)

12. Higher Ptot enhances coupling of RMP with plasma: smaller ELMs and toroidal asymmetries. deposited energy [kJ] • Without RMP (blue curves): • average ELM energy almost does not change with q95 with variability of deposited energy of about 50%. • wetted area change rate increases linearly with q95 • on average no toroidal asymmetry. • RMP at Ptot = 5 MW (red curves): • reduces average energy by factor of 2 • toroidal asymmetry depends on q95 symmetry of wf - Rw symmetry of Edep - RE • RMP at Ptot = 9 MW (green curves): • reduces ELM energy even better (8 kJ  3 kJ) • toroidal asymmetries are slightly higher M.W. Jakubowski, et al., PSI San Diego (2010)

13. 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 q95 M.W. Jakubowski, et al., PSI San Diego (2010)

14. Population curve of ELMs has two subgroups  different ELMs? • Introducing RMP at 6 MWheating 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)

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

16. Amplitude and frequency is very sensitive to q95 T. Evans, et al., IAEA, Geneve (2008) M.W. Jakubowski, et al., PSI San Diego (2010)

17. 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 q95significantly 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)

18. 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)

19. 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 q95 M.W. Jakubowski, et al., PSI San Diego (2010)

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