A mechanism of bifurcation to strongly sheared toroidal rotation in the radiatively improved mode in TEXTOR-94

A mechanism, based on the dependence of the anomalous plasma viscosity on the velocity gradient, is proposed to explain a strong shearing of the ion toroidal velocity in the radiatively improved (RT) mode in TEXTOR-94 with unbalanced neutral injection. The conditions of the bifurcation into this plasma state with a barrier in the ion momentum and heat transport are analysed, and it is demonstrated that the density peaking caused by puffing of impurities is of principal importance to achieve them. The time evolution of the ion toroidal velocity and temperature by the transition into the RI mode is modelled.