Change in ion orbit loss, intrinsic rotation and particle pinch across the L–H transition in DIII-D plasmas

Two interesting L–H transition phenomena are further investigated in DIII-D. Firstly, it has previously been observed in co-current rotating DIII-D discharge #118897 that at the L–H transition there is an immediate increase in the measured carbon toroidal co-rotation velocities for ρ ≤ 0.94, as would be expected for improved confinement in H-mode, but for the edge pedestal (0.94 < ρ < 1.0) there is a decrease in the measured carbon toroidal co-rotation that persists for about 20 ms before also beginning to increase. Calculations indicate that ion orbit loss of predominantly counter-current rotating ions in the edge plasma, which produces an intrinsic co-rotation, is reduced in H-mode relative to L-mode, consistent with the observed reduction of the measured carbon co-rotation immediately after the L–H transition. Secondly, a theoretical expression for the radial particle pinch (predominantly electromagnetic) predicted a weak pinch when evaluated for the measured L-mode plasma conditions prior to the L–H transition, but predicted a strongly inward pinch velocity when evaluated for the measured H-mode plasma conditions immediately following the L–H transition. We have now refined the data fitting and repeated this investigation for the same and two additional L–H transitions in DIII-D, essentially confirming the generality of the previous results.