An improved confinement state can be attained by imposing a radial electric field at the plasma edge. This is characterized by a change of the Er structure. A charge conservation equation with a diffusion term has been solved to explain this mechanism. Various types of Er structures with multiple peaks are allowed for the same boundary condition. The relationship between the voltage and the current is obtained by numerical calculation. Both stable and unstable regions exist in the stationary solutions and their boundary points are critical points for transition from one state to another. Multiple transitions and hysteresis are predicted. The magnitude of the collision frequency affects the existence of solutions with multiple peaks.