Electrons are injected into an afterglow plasma confined in an ℓ = 3 stellarator in order to raise the velocity of poloidal rotation. A steady shock-like structure characterized by a steep density gradient is observed near the critical rotational speed. Strong enhancement of the diffusion rate occurs at higher radial electric fields, accompanied by large-amplitude density fluctuations. Vortices are generated at the three corners of the triangular magnetic surfaces when the radial electric field is reversed inside the plasma.