3D Magnetic Perturbation Effects on Transport in Tokamaks

Recent experimental results in DIII-D H-mode plasmas, with a constant level of applied n=3 perturbation fields, have revealed dramatic particle, energy and momentum transport changes simply by altering the relative toroidal phase between the intrinsic n=1 and 2 field-errors and the applied n=3 perturbation field. Here, we present a summary of the experimental observations, including changes in the turbulence and MHD behavior in configurations with either constructive or destructive interference between the intrinsic n=1 and 2 fields and the applied n=3 field. A particularly interesting aspect of these results is that the energy confinement increases by $\sim$35\% when the intrinsic and applied perturbation fields are relatively well aligned to produce a larger total radial field. Similar increases are seen in the particle and momentum confinement. These observations are compared to a hypothesis connecting the structure of the 3D radial magnetic perturbation field to the changes in transport.