Transport-driven scrape-off layer flows and the x-point dependence of the L-H power threshold in Alcator C-Mod -: art. no. 056111

被引:88
作者
LaBombard, B [1 ]
Rice, JE [1 ]
Hubbard, AE [1 ]
Hughes, JW [1 ]
Greenwald, M [1 ]
Granetz, RS [1 ]
Irby, JH [1 ]
Lin, Y [1 ]
Lipschultz, B [1 ]
Marmar, ES [1 ]
Marr, K [1 ]
Mossessian, D [1 ]
Parker, R [1 ]
Rowan, W [1 ]
Smick, N [1 ]
Snipes, JA [1 ]
Terry, JL [1 ]
Wolfe, SM [1 ]
Wukitch, SJ [1 ]
机构
[1] MIT, Plasma Sci & Fus Ctr, Cambridge, MA 02139 USA
关键词
D O I
10.1063/1.1876294
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
Factor of similar to 2 higher power thresholds for low- to high-confinement mode transitions (L-H) with unfavorable x-point topologies in Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] are linked to flow boundary conditions imposed by the scrape-off layer (SOL). Ballooning-like transport drives flow along magnetic field lines from low- to high-field regions with toroidal direction dependent on upper/lower x-point balance; the toroidal rotation of the confined plasma responds, exhibiting a strong counter-current rotation when Bx del B points away from the x point. Increased auxiliary heating power (rf, no momentum input) leads to an L-H transition at approximately twice the edge electron pressure gradient when Bx del B points away. As gradients rise prior to the transition, toroidal rotation ramps toward the co-current direction; the H mode is seen when the counter-current rotation imposed by the SOL flow becomes compensated. Remarkably, L-H thresholds in lower-limited discharges are identical to lower x-point discharges; SOL flows are also found similar, suggesting a connection. (c) 2005 American Institute of Physics.
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页数:10
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