Confinement bifurcation initiated by plasma current profile and toroidal electric field perturbations in the TUMAN-3M tokamak

The results of the experimental study of confinement mode bifurcation performed on the TUMAN-3M tokamak are reported. As a trigger of confinement mode switching, plasma current ramp-up/-down or magnetic compression/decompression is used. It is found that the possibility and direction of confinement mode switching are correlated not with plasma current profile perturbation (peaking or broadening) but with the sign of toroidal electric field perturbation. A model connecting confinement bifurcation and toroidal electric field perturbation through the perturbation of the radial electric field is used to describe the phenomena observed in all eight scenarios investigated. This model ascribes the radial electric field generation to the non-compensated Ware drift of banana electrons at the TUMAN-3M peripheral plasma, where . Measurements of turbulence level and poloidal plasma rotation using microwave reflectometry are used to validate the model.