Formation of electric potential in a tokamak edge by limiter biasing

It was found in the HYBTOK-II tokamak that the negative change of the electric potential of the plasma by a limiter biasing is influenced sensitively by the magnetic configuration in the SOL, but the positive change is not. The concept of effective area is introduced to explain the potential change due to a horizontal shift of plasma column in the negative biasing. Using such a concept, a simple model for the formation of electric potential in a plasma for both a cold and an electron-emitting limiter is presented. The model explains qualitatively the experimental results.>