Transport-driven scrape-off layer flows and the x-point dependence of the L-H power threshold in Alcator C-Mod

Journal Article · Sun May 15 04:00:00 EDT 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.1876294· OSTI ID:20736576

LaBombard, B; Rice, J E; Hubbard, A E; Hughes, J W; Greenwald, M; Granetz, R S; Irby, J H; Lin, Y; Lipschultz, B; Marmar, E S; Marr, K; Mossessian, D; Parker, R; Rowan, W; Smick, N; Snipes, J A; Terry, J L; Wolfe, S M; Wukitch, S J ^[1]

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1. Massachusetts Institute of Technology, Plasma Science and Fusion Center, 175 Albany Street, Cambridge, Massachusetts 02139 (United States)

Factor of {approx}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{nabla}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{nabla}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.

• OSTI ID: 20736576
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 12; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
BOUNDARY CONDITIONS
H-MODE PLASMA CONFINEMENT
PLASMA
PLASMA PRESSURE
PLASMA SCRAPE-OFF LAYER