  We report results from experiments performed to study how a DC bias with
respect to the plasma potential is affecting the plasma states in the toroidal
geometry of the Blaamann device in Tromso. In the experiments discussed here, a
ring with smaller diameter than the limiter was centered inside the bulk of the
plasma and its bias varied with respect to the plasma potential. In the
electron saturation current regime of the ring, a significant reduction of the
fluctuation levels was observed, and a shear in the poloidal velocity occurred
at the low-field side of the ring. This shear was positioned at the same radial
position as the maximum of the radial transport when the ring was left floating
or biased in the ion saturation current regime. For the latter ring biases, the
poloidal velocities had no shear on the low-field side of the ring. Without the
velocity shear, the radial transport was similar to previous experiments
without ring. With the velocity shear, the radial transport was destroyed. This
plasma state, with very low radial transport and fluctuation levels as well as
plasma densities around 1017 m-3, is believed to provide a suitable plasma for
wave propagation studies in a magnetized plasma with curved magnetic field
lines without end effects.
