The operational phase-space of the edge plasma and its sensitivity to magnetic topology in Alcator C-Mod

B. LaBombard, N. Smick, M. Greenwald, J.W. Hughes, B. Lipschultz, K. Marr, J.L. Terry

Research output: Contribution to journalArticlepeer-review


The range of 'edge plasma states' (i.e., the combination of densities, temperatures and gradients in the scrape-off layer near the separatrix) accessible to a tokamak are highly restricted. Experiments in Alcator C-Mod suggest that this restriction is a consequence of electromagnetic fluid drift turbulence (EMFDT), which sets the cross-field transport levels; plasma states are constrained to lie in a narrow region of EMFDT 'phase-space' defined by poloidal beta gradient (α) and normalized plasma collisionality. Recent experiments have investigated this behavior over an increased parameter range in lower- and upper-null (LSN/USN) discharges. L-mode edge pressure gradients are found to exhibit clear sensitivity to magnetic topology, favoring higher α for LSN compared to USN. These variations may be caused, in part, by the different edge plasma flow patterns in LSN versus USN. Such flows arise from a ballooning-like transport drive and can produce a topology-dependent modulation in the toroidal plasma rotation.
Original languageEnglish
Pages (from-to)517-521
Number of pages5
JournalJournal of Nuclear Materials
Issue number1-3
Publication statusPublished - 15 Jun 2007

Cite this