Effect Of Magnetic Perturbations On Turbulence-Flow Dynamics At The L-H Transition On Diii-D

Detailed 2D turbulence measurements from the DIII-D tokamak provide an explanation for how resonant magnetic perturbations (RMPs) raise the L-H power thresholdPLH [P. Gohil et al., Nucl. Fusion 51, 103020 (2011)] in ITER-relevant, low rotation, ITER-similar-shape plasmas with favorable iondel B direction. RMPs simultaneously raise the turbulence decorrelation rateDeltaomegaD and reduce the flow shear rateomegashear in the stationary L-mode state preceding the L-H transition, thereby disrupting the turbulence shear suppression mechanism. RMPs also reduce the Reynolds stress drive for poloidal flow, contributing to the reduction ofomegashear. On the similar to 100 mu s timescale of the L-H transition, RMPs reduce Reynolds-stress-driven energy transfer from turbulence to flows by an order of magnitude, challenging the energy depletion theory for the L-H trigger mechanism. In contrast, non-resonant magnetic perturbations, which do not significantly affectPLH, do not affectDeltaomegaD and only slightly reduceomegashear and Reynolds-stress-driven energy transfer.