- Rice, JE
- Gao, C
- Reinke, ML
- Diamond, PH
- Howard, NT
- Sun, HJ
- Cziegler, I
- Hubbard, AE
- Podpaly, YA
- Rowan, WL
- Terry, JL
- Chilenski, MA
- Delgado-Aparicio, L
- Ennever, PC
- Ernst, D
- Greenwald, MJ
- Hughes, JW
- Ma, Y
- Marmar, ES
- Porkolab, M
- White, AE
- Wolfe, SM
- et al.
Several seemingly unrelated effects in Alcator C-Mod ohmic L-mode plasmas are shown to be closely connected: non-local heat transport, core toroidal rotation reversals, energy confinement saturation and up/down impurity density asymmetries. These phenomena all abruptly transform at a critical value of the collisionality. At low densities in the linear ohmic confinement regime, with collisionality ν* 0.35 (evaluated inside of the q = 3/2 surface), heat transport exhibits non-local behaviour, core toroidal rotation is directed co-current, edge impurity density profiles are up/down symmetric and a turbulent feature in core density fluctuations with kθ up to 15 cm-1 (kθρs ∼ 1) is present. At high density/collisionality with saturated ohmic confinement, electron thermal transport is diffusive, core rotation is in the counter-current direction, edge impurity density profiles are up/down asymmetric and the high k θ turbulent feature is absent. The rotation reversal stagnation point (just inside of the q = 3/2 surface) coincides with the non-local electron temperature profile inversion radius. All of these observations suggest a possible unification in a model with trapped electron mode prevalence at low collisionality and ion temperature gradient mode domination at high collisionality. © 2013 IAEA, Vienna.