Experimental investigation of marfes and the density limit in the ASDEX upgrade
V Mertens; W Junker; M Laux; M Schittenhelm; K Buchl; F Mast; A Carlsont; A Field; C Fuchs; O Gehre; O Gruber; A Hermann; G Haas; A Kallenbach; M Kaufmann; W Koppendorfer; K Lackner; G Lieder; S Pitcher; J Neuhauser; F Ryter; H Salzmann; W Sandmann; K -H Steuer; M Weinlich; U Wenzel; H Zohm; Asdex Upgrade Team; V Mertens; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; W Junker; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; M Laux; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; M Schittenhelm; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; K Buchl; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; F Mast; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; A Carlsont; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; A Field; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; C Fuchs; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; O Gehre; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; O Gruber; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; A Hermann; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; G Haas; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; A Kallenbach; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; M Kaufmann; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; W Koppendorfer; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; K Lackner; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; G Lieder; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; S Pitcher; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; J Neuhauser; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; F Ryter; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; H Salzmann; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; W Sandmann; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; K -H Steuer; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; M Weinlich; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; U Wenzel; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; H Zohm; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany; Asdex Upgrade Team; EURATOM Assoc., Max-Planck-Inst. fur Plasmaphys., Garching bei Munchen, Germany
Журнал:
Plasma Physics and Controlled Fusion
Дата:
1994-08-01
Аннотация:
In the ASDEX Upgrade, X-point marfe formation and its behaviour up to the density limit is investigated in gas-fuelled ohmically-heated single-null discharges over a wide range of parameters: I<sub>p</sub>=0.6-1.2 MA, B<sub>TF</sub>=1.35-2.4 T, a plasma elongation of 1.6 and Z<sub>eff</sub><2. The standard-ion Del B drift is directed towards the X-point. At medium electron densities inevitably a marfe develops in the vicinity of the active X-point. The marfe formation is consistent with a model of thermal instabilities in the radiating edge plasma. Moreover, stable steady-state operation is demonstrated with marfes which can extend significantly into the bulk plasma. The density limit is always connected with quick marfe expansion and movement followed by mode-locking leading to a major disruption. The limit scales linearly with I<sub>p</sub> and is in good agreement with the Greenwald density limit scaling. The resulting experimental Hugill limit is n<sub>e</sub>Rq<sub>95</sub>/B<sub>TF</sub>=2.8*10<sup>20</sup>) m<sup>-2</sup> T<sup>-1</sup>. Reversal of the ion Del B drift direction away from the target has a detrimental effect on the density limit.
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