[en] The velocities of helium ions and neutrals are derived from Doppler shifted spectral lines He II 4686 A and He I 5876 A respectively. The ion velocity proves to be in accordance with the speed of rotating spokes which are usually observed in the build-up phase of rotating plasmas. It is demonstrated that the spoke velocity represents the plasma mass motion. Braking of plasma motion and acceleration of the neutrals to a value near Alven's critical velocity occurs within 10 μs. (orig.)