A E Hubbard et al 2002 Plasma Phys. Control. Fusion 44 A359 doi:10.1088/0741-3335/44/5A/338
A E Hubbard1, B A Carreras2, R L Boivin1,3, J W Hughes1, E S Marmar1, D Mossessian1 and S J Wukitch
Show affiliationsLocal edge electron parameters are measured in the Alcator C-Mod tokamak, during discharges in which input power is continuously ramped up and down, leading to transitions from the low-confinement mode (L-mode) to high-confinement mode (H-mode) mode and back to L-mode. This allows measurement of the accessible portions of the non-monotonic flux-gradient relationship proposed by models of the H-mode as a critical transition. Results are consistent with a dependence of conductivity χ on the temperature gradient, where a very sharp decrease in χ occurs above a critical ∇T. Other possible flux-gradient relations are also examined, and the data are compared with theoretical formulations. The initial transient of pedestal energy in the first few ms after the L-H transition is also analysed and found to be consistent with a sudden decrease in χ across the pedestal region.
Issue 5A (May 2002)
Received 5 September 2001
Published 29 April 2002
A E Hubbard et al 2002 Plasma Phys. Control. Fusion 44 A359
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