Measurements of three-dimensional flows induced by magnetic islands

Magnetic reconnection and the resulting complex magnetic field geometries are fundamental aspects of our understanding of both space and laboratory plasmas. We report on the observation of three-dimensional (3D) impurity ion flow perturbation due to counterstreaming flows in the boundary plasma of the DIII-D tokamak. These counterstreaming flows arise not due to the magnetic reconnection itself but from the subsequent creation of collections of isolated flux tubes called magnetic islands. The magnetic islands form chains that wrap helically around the tokamak and modify local pressure balance generating a distinctive pattern of velocity perturbations that confirm long-standing 3D transport simulations. EMC3-EIRENE fluid modeling shows that these velocity perturbations arise from parallel pressure gradients that result principally from the radial temperature gradient across the magnetic islands and are supported by a momentum-loss feedback loop.