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          Institute: MPI für Plasmaphysik     Collection: Articles, Books, Inbooks     Display Documents



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ID: 56114.0, MPI für Plasmaphysik / Articles, Books, Inbooks
ELM frequency control by continuous small pellet injection in ASDEX Upgrade
Authors:Lang, P. T.; Neuhauser, J.; Horton, L. D.; Eich, T.; Fattorini, L.; Fuchs, J. C.; Gehre, O.; Herrmann, A.; Ignacz, P.; Jakobi, M.; Kalvin, S.; Kaufmann, M.; Kocsis, G.; Kurzan, B.; Maggi, C.; Manso, M. E.; Maraschek, M.; Mertens, V.; Mück, A.; Murmann, H. D.; Neu, R.; Nunes, I.; Reich, D.; Reich, M.; Saarelma, S.; Sandmann, W.; Stober, J.; Vogl, U.; ASDEX Upgrade Team
Language:English
Date of Publication (YYYY-MM-DD):2003
Title of Journal:Nuclear Fusion
Journal Abbrev.:Nucl. Fusion
Volume:43
Issue / Number:10
Start Page:1110
End Page:1120
Copyright:Copyright © Institute of Physics and IOP Publishing Limited 2003
Review Status:Peer-review
Audience:Experts Only
Abstract / Description: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.
Free Keywords:H-MODE DISCHARGES, MAGNETOHYDRODYNAMIC STABILITY, DIVERTOR, CONFINEMENT, TOKAMAK, JET, PEDESTAL, DRIFT,
FLUX
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Plasmaphysik/Tokamak Scenario Development (E1)
External Affiliations:Centro de Fusão Nuclear, Associacão EURATOM/IST, Instituto Superior Técnico, 1049-001 Lisboa, Portugal; KFKI-RMKI, PO Box 49, H-1525 Budapest, Hungary; FH Amberg-Weiden, Abt. Amberg, Kaiser-Wilhelm-Ring 23, 92224 Amberg, Germany; Helsinki University of Technology, Euratom-TEKES Association, PO Box 2200, FIN-02015 HUT, Finland
Identifiers:DOI:10.1088/0029-5515/43/10/012
URL:http://stacks.iop.org/0029-5515/43/1110
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