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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 Team^1)
 
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 ( H_{98 - 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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