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(EX/C2-1) Tolerable ELMs in Conventional and Advanced Scenarios at ASDEX Upgrade

O. Gruber1), S. Guenter1), A. Herrmann1), L.D. Horton1), P.T. Lang1), M. Maraschek1), S. Saarelma2), A.C. Sips1), J. Stober1), W. Suttrop1), H. Zohm1), ASDEX Upgrade Team1)
1) Max-Planck-Institut für Plasmaphysik, EURATOM-Assoc., Garching, Germany
2) Helsinki University of Technology, EURATOM-Tekes Assoc., Espoo, Finland

Abstract.  Recent ASDEX Upgrade experiments integrated benign type II ELMs (tolerable peak heat loads on target plates) with high performance. In both conventional and advanced H-modes, the operation window with type II ELMs was extended towards q95 > 3.5 in close to double null configurations at sufficient high edge pedestal density above 50% of the Greenwald density. Type I ELMs are suppressed at almost constant pedestal parameters presumably due to a change in edge stability provided by higher edge magnetic shear, and at the same confinement level. Since conventional reactor designs are optimised at q95 around 3 operation with type II ELMs has to compensate the required higher q-value by advanced performance. This was achieved in advanced H-mode scenarios integrating high $ \beta_{N}^{}$ > 3.5, improved confinement via density peaking ( H98 - P = 1.3), and densities of 90% of Greenwald density with type II ELMs. Another way to mitigate ELMs is active type I ELM control by means of hydrogen or impurity injection. Using small hydrogen pellets we demonstrated an enhancement of the ELM frequency to almost the pellet rate of 20 Hz and a considerable reduction of the energy loss/ELM by more than a factor of 3.

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IAEA 2003