[en] Heavy Ion Beam Probe diagnostics was used to study plasma potential and density in the regimes with improvement in confinement on the T-10 tokamak. Time-spatial potential distribution was analyzed during the formation of transport barriers. The time evolution of the potential profile shows simultaneous formation of the internal negative potential well and external layer with strong E_r, during the simultaneous formation of the internal and external transport barriers. The time history of the plasma potential in the inner region (0.6 < ρ < 1) shows its clear correlation with the D_α intensity. (author)