Evolution of the Radial Electric Field in a JET H-mode Plasma

Results are presented from recent measurements of the toroidal and poloidal rotation velocity in the pedestal region of an evolving JET H-mode plasma in which several transitions occur. These cover a range of plasma confinement regimes including L-mode, the L-H transition, ELM-free H-mode, ELMy H-mode and the H-L transition. Detailed edge plasma measurements show no spin-up of the poloidal rotation velocity prior to the L-H transition. However, directly following the transition to H-mode, the poloidal rotation velocity just inside the last closed flux surface increases to a maximum of 8(±2) km s-1. As the H-mode continues to evolve, the largest values of edge toroidal and poloidal rotation velocity gradients are clearly associated with the ELM-free H-mode. Following the ELM-free phase, large, 1.4MJ ELMs are observed to erode the pedestal ion and electron temperature profiles along with the edge toroidal rotation gradient but have little impact on the overall poloidal rotation velocity shear. Maximum values of ±9 km s-1 are observed in the poloidal rotation velocity profile and have a significant effect on the temporal development of the edge plasma radial electric field.
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