Analysis of structure and transition of radial electric field in helical systems

A set of transport equations is analysed, including the bifurcation of the radial electric field in toroidal helical systems. Calculations are made simulating the compact helical systems experiments. Both hard and soft transitions are found in the profile of the radial electric field. Whether the electric domain interface exists or not is found to depend on the ratio of the electron temperature to the ion temperature. The structure of the electric domain interface is also studied. The steep gradient of the radial electric field is obtained and the width of the electric domain interface is determined by the anomalous diffusivity of the electric field. The region where the electron root and ion root co-exist is obtained when changing the density or the heating power of electrons. The various types of the electrostatic potential structures are found. The condition for the turbulence suppression is examined in the parameter regime studied here.