Effects of the toroidal electric field perturbation on the radial electric field and confinement bifurcation in the TUMAN-3M tokamak

Plasma current profile was modified using current Ramp Up and Down or, alternatively, magnetic compression scenarios on the TUMAN-3M tokamak. It was found that the fast current profile evolutions in these experiments led to confinement mode transitions. However, the direction of the confinement bifurcation (improvement at the L-H transition, or degradation at the H-L transition) correlates with the sign of toroidal electric field perturbation, rather than with the peaking or broadening of current profile itself. A novel mechanism of the radial electric field generation based on 'non-ambipolar' radial drift of electrons and ions is proposed. This mechanism is capable of explaining the observed peculiarities of the confinement evolution. (author)