[en] Advances in potential formation have led to remarkable discoveries on the effects of radial electric field distribution on turbulence suppression and transverse loss reduction. In order to study the improvement in plasma confinement because of the formation of plasma confinement potential, we constructed a multi-channel microwave interferometer system that can measure the density and density fluctuation radial profiles in a single plasma shot. We obtained clear density fluctuation suppression by the formation of the plasma confinement potential. Therefore, we have a powerful diagnostic tool with which to study the improvement in plasma confinement. (author)