Critical gradients and plasma flows in the edge plasma of Alcator C-Mod

Journal Article · Thu May 15 04:00:00 EDT 2008 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2838246· OSTI ID:21120361

LaBombard, B; Hughes, J W; Smick, N; Marr, K; McDermott, R; Reinke, M; Greenwald, M; Lipschultz, B; Terry, J L; Whyte, D G ^[1]; Graf, A ^[2]; Zweben, S J ^[3]

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1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2. University of California, Davis, California 95616 (United States)
3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

Recent experiments have led to a fundamental shift in our view of edge transport physics; transport near the last-closed flux surface may be more appropriately described in terms of a critical gradient phenomenon rather than a diffusive and/or convective paradigm. Edge pressure gradients, normalized by the square of the poloidal magnetic field strength, appear invariant in plasmas with the same normalized collisionality, despite vastly different currents and magnetic fields--a behavior that connects with first-principles electromagnetic plasma turbulence simulations. Near-sonic scrape-off layer (SOL) flows impose a cocurrent rotation boundary condition on the confined plasma when Bx{nabla}B points toward the active x-point, suggesting a link to the concomitant reduction in input power needed to attain high-confinement modes. Indeed, low-confinement mode plasmas are found to attain higher edge pressure gradients in this configuration, independent of the direction of B, evidence that SOL flows may affect transport and 'critical gradient' values in the edge plasma.

• OSTI ID: 21120361
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 15; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
BOUNDARY CONDITIONS
MAGNETIC FIELDS
MAGNETIC SURFACES
PLASMA
PLASMA CONFINEMENT
PLASMA SCRAPE-OFF LAYER
PRESSURE GRADIENTS
ROTATION
TURBULENCE