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ELM frequency control by continuous small pellet injection in ASDEX Upgrade

MPS-Authors
/persons/resource/persons109762

Lang,  P. T.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Horton,  L. D.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109017

Eich,  T.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109124

Fuchs,  J. C.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109152

Gehre,  O.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109371

Herrmann,  A.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Jakobi,  M.
Experimental Plasma Physics 2 (E2), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109578

Kaufmann,  M.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

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Kurzan,  B.
Experimental Plasma Physics 2 (E2), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109863

Maggi,  C.
Experimental Plasma Physics 4 (E4), Max Planck Institute for Plasma Physics, Max Planck Society;

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Maraschek,  M.
Experimental Plasma Physics 2 (E2), Max Planck Institute for Plasma Physics, Max Planck Society;

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Mertens,  V.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Neu,  R.
Experimental Plasma Physics 4 (E4), Max Planck Institute for Plasma Physics, Max Planck Society;

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Reich,  M.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Sandmann,  W.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Stober,  J.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

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Citation

Lang, P. T., Neuhauser, J., Horton, L. D., Eich, T., Fattorini, L., Fuchs, J. C., et al. (2003). ELM frequency control by continuous small pellet injection in ASDEX Upgrade. Nuclear Fusion, 43(10), 1110-1120. doi:10.1088/0029-5515/43/10/012.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0027-242B-6
Abstract
Injection of cryogenic deuterium pellets has been successfully applied in ASDEX Upgrade for external edge localized mode (ELM) frequency control in type-I ELMy H-mode discharge scenarios. A pellet velocity of 560 m s⁻¹ and a size of about 6 × 10¹⁹ D-atoms was selected for technical reasons, although even lower masses were found sufficient to trigger ELMs. A moderate repetition rate close to 20 Hz was chosen to avoid over-fuelling of the core plasma. Pellet sequences of up to 4 s duration were injected into discharges close to the L–H threshold, intrinsically developing large compound ELMs at a rate of 3 Hz. With pellet injection, these large ELMs were completely replaced by smaller type-I ELMs at the much higher pellet frequency, accompanied by a slight increase of density and even of stored energy. This external ELM control could be repeatedly switched on and off by just interrupting the pellet train. ELMs were triggered in less than 200 µs after pellet arrival at the plasma edge, at which time only a fraction of the pellet has been ablated, forming a rather localized, three-dimensional plasmoid, which drives the edge unstable well before the deposited mass is spread toroidally. The pellet controlled case has also been compared with a discharge at a somewhat lower density, but with otherwise rather similar data, developing spontaneous 20 Hz type-I ELMs. Despite the different trigger mechanisms, the general ELM features turn out to be qualitatively similar, possibly because of the similarity of the two cases in terms of ELM relevant parameters. The scaling with background plasma, heating power, pellet launch parameters, etc over a larger range still remains to be investigated.