Interaction of magnetic islands with turbulent electron temperature fluctuations in DIII-D and in GENE nonlinear gyrokinetic simulations

Abstract

We present localized measurements of interactions between neoclassical tearing modes (NTMs) and turbulent electron temperature fluctuations ((T) over tilde (e)) in the expected k theta rho(s)=0-0.5 wave-number range of the ion temperature gradient (ITG) instability measured via correlation electron cyclotron emission (k(theta) and rho(s) are the poloidal wave-number and ion-sound Larmor radius, respectively). Comparison to GENE gyrokinetic simulations, shows qualitative agreement with (T) over tilde (e) being reduced (increased) inside (outside) of the islands due to modified local gradients, and (T) over tilde (e) being higher (lower) in the region outside the island where lower (higher) flow shear is expected due to radially asymmetric island shape. These results are consistent with previously reported modifications of long and intermediate wavelength turbulent density fluctuations and cross-field electron thermal diffusivity reduction at the O-point of magnetic islands. Interestingly, a 30% increase of (T) over tilde (e) is detected at the NTM rational surface when the island width is a few times rho(s), which is replicated by GENE through zonal flow damping due to the destroyed magnetic field topology of the NTM rational surface.