The Pump-Out Effect as a Trigger for the Electron to Ion Root Transition in TJ-II

This is the authors' abstract. We don't add key points for this paper.

In this paper, we study electron to ion root confinement transitions triggered by Electron Cyclotron Resonant Heating switch-off when the line-averaged electron density is sufficiently high and while Neutral Beam Injection heating is on. We use a Heavy Ion Beam Probe system to document the transition in considerable detail. The transition occurs in two phases. An initial, fast phase is characterized by a rapid, global decay of the plasma potential and the concomitant establishment of an edge radial electric field shear layer. This phase is induced by the pump-out effect, as documented using simultaneous measurements of the evolution of the plasma potential at different radial locations. This initial, fast phase is followed by a slow phase during which the profiles adjust to the new edge and heating conditions via transport.