The control of the well-type radial potential profile in a dc plasma by applying bias potential, V-E, to the end plate is investigated experimentally. The experimental evidence that a plasma space potential, Phi (p), increases at the circumference of the plasma with the increase of V-E is interpreted qualitatively by the experimental results of the current drawn by the segmented end plate, and of the relationship of Phi (p) to V-E. For the dc discharge the value of Phi (p) at the center of the plasma is naturally settled on the value somewhat lower than the anode potential, the electron sheath therefore appears in front of the end plate and expands radially as V-E is increased. Electrons are drawn from the circumference of the plasma to the end plate, inducing the nonambipolar radial electron flux. Since the cross-field electron mobility is not sufficiently large, the inwardly directed radial electric field becomes stronger. The role of electron sheath formed is crucial in actively controlling the radial potential profile in the dc plasma. (C) 2001 American Institute of Physics.