Ion-scale turbulence modified by applied magnetic islands in DIII-D

The interaction of ion-scale turbulence with 3D magnetic fields including applied magnetic islands is an emerging area of interest for both tokamaks and stellarators. We present 2D maps of density turbulence characteristics in the presence of large quasi-static magnetic islands using beam emission spectroscopy (BES) at DIII-D. A slowly-rotating (f ~ 1 Hz) n=1 resonant magnetic perturbation (RMP) generated m=2 islands in limited L-mode plasmas. The island structure from vacuum calculations is comparable with measured electron temperature contours. Density fluctuations are enhanced several-fold near the island X-point and reduced near the O-point, compared to the unperturbed equilibrium, in qualitative agreement with predictions from slab models. The turbulence phase velocity and radial correlation length are also modified by the island. The temporal dynamics of the turbulence during the RMP application and island formation are also analyzed. When higher applied torque prevents island formation, the shielded RMP induces a weaker, more radially-uniform response.