paper

Effect of magnetic perturbations on turbulence-flow dynamics at the L-H transition on DIII-D

arXiv:2004.12003 · doi:10.1063/1.5145207

Abstract

Detailed 2D turbulence measurements from the DIII-D tokamak provide an explanation for how resonant magnetic perturbations (RMPs) raise the L-H power threshold $P_{LH}$ [P. Gohil et al., Nucl. Fusion 51, 103020 (2011)] in ITER-relevant, low rotation, ITER-similar-shape plasmas with favorable ion $\nabla B$ direction. RMPs simultaneously raise the turbulence decorrelation rate $I^ I ¨ _{D}$ and reduce the flow shear rate $I ¨ _{shear}$ 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 of $I ¨ _{shear}$ On the ~100 Î¼s 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 affect $P_{LH}$ , do not affect $I^ I ¨ _{D}$ and only slightly reduce $I ¨ _{shear}$ and Reynolds-stress-driven energy transfer.

The following article has been submitted to Physics of Plasmas