H mode behaviour induced by radially outward fields imposed in TEXTOR

Edge polarization experiments were performed on TEXTOR showing that H mode behaviour can be set up with both positive and negative radial electric fields. The H mode can be sustained in the presence of auxiliary heating, and improvements in energy confinement of up to about 1.4 and in particle confinement of 2 to 2.5 were obtained with positive bias. First indications are that the particle confinement might increase more with negative bias. The viscous damping of poloidal rotation is found to be in good agreement with some versions of neoclassical theory. An expression can therefore be derived for the minimum non-ambipolar radial current that must be set up in the plasma edge to provoke an L to H transition.