H-mode development in TEXT-U limiter plasmas
D R Roberts; R V Bravenec; R D Bengtson; D L Brower; G Cima; T P Crowley; A Darbar; P H Edmonds; H Gasquet; K W Gentle; G A Hallock; J W Heard; P D Hurwitz; Y Jiang; Y Y Karzhavin; J Lierzer; A Nikitin; A Ouroua; D M Patterson; P E Phillips; S Reedy; B Richards; W L Rowan; P M Schoch; D C Sing; E R Solano; D Storek; C Watts; D Winslow; A J Wootton; L Zeng; B Zhang; S-B Zheng; D R Roberts; University of Texas at Austin, Austin, TX 78712, USA; R V Bravenec; University of Texas at Austin, Austin, TX 78712, USA; R D Bengtson; University of Texas at Austin, Austin, TX 78712, USA; D L Brower; University of Texas at Austin, Austin, TX 78712, USA; G Cima; University of Texas at Austin, Austin, TX 78712, USA; T P Crowley; University of Texas at Austin, Austin, TX 78712, USA; A Darbar; University of Texas at Austin, Austin, TX 78712, USA; P H Edmonds; University of Texas at Austin, Austin, TX 78712, USA; H Gasquet; University of Texas at Austin, Austin, TX 78712, USA; K W Gentle; University of Texas at Austin, Austin, TX 78712, USA; G A Hallock; University of Texas at Austin, Austin, TX 78712, USA; J W Heard; University of Texas at Austin, Austin, TX 78712, USA; P D Hurwitz; University of Texas at Austin, Austin, TX 78712, USA; Y Jiang; University of Texas at Austin, Austin, TX 78712, USA; Y Y Karzhavin; University of Texas at Austin, Austin, TX 78712, USA; J Lierzer; University of Texas at Austin, Austin, TX 78712, USA; A Nikitin; University of Texas at Austin, Austin, TX 78712, USA; A Ouroua; University of Texas at Austin, Austin, TX 78712, USA; D M Patterson; University of Texas at Austin, Austin, TX 78712, USA; P E Phillips; University of Texas at Austin, Austin, TX 78712, USA; S Reedy; University of Texas at Austin, Austin, TX 78712, USA; B Richards; University of Texas at Austin, Austin, TX 78712, USA; W L Rowan; University of Texas at Austin, Austin, TX 78712, USA; P M Schoch; University of Texas at Austin, Austin, TX 78712, USA; D C Sing; University of Texas at Austin, Austin, TX 78712, USA; E R Solano; University of Texas at Austin, Austin, TX 78712, USA; D Storek; University of Texas at Austin, Austin, TX 78712, USA; C Watts; University of Texas at Austin, Austin, TX 78712, USA; D Winslow; University of Texas at Austin, Austin, TX 78712, USA; A J Wootton; University of Texas at Austin, Austin, TX 78712, USA; L Zeng; University of Texas at Austin, Austin, TX 78712, USA; B Zhang; University of Texas at Austin, Austin, TX 78712, USA; S-B Zheng; University of Texas at Austin, Austin, TX 78712, USA
Журнал:
Plasma Physics and Controlled Fusion
Дата:
1996-08-01
Аннотация:
H-mode transitions in TEXT-U limiter plasmas have been observed at and kA ( kW) with at least 300 kW of central electron-cyclotron heating (ECH). These are dithering transitions which are induced by sawtooth crashes and display the typical signatures of H-modes ( drop, spontaneous density increase, evidence of a transport barrier). However, they show only a slight improvement over L-mode energy confinement. The vessel walls are boronized and conditioned prior to experiments to achieve low-impurity influx and particle recycling. Discharges which undergo transitions are fuelled almost entirely on residual recycling. Transitions are observed when limited on a toroidally localized top or bottom limiter and, more often, when the limiter surface is `fresh', which is achieved by alternating between top and bottom limiters on successive shots. No strong dependence upon the distance from the low-field-side limiter has been found. Transitions are not yet observed when limited on the high-field-side wall tiles or in the case of TEXT-U diverted configurations. Preliminary measurements with the 2 MeV heavy-ion beam probe (HIBP) (in the core) and Langmuir probes (in the edge) indicate that the plasma potential drops outside the q = 1 radius while only small changes are observed in the density fluctuation level.
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