Electric Field Bifurcation and Transition in CHS Heliotron/Torsatron

Transition in radial electric field has been observed in CHS plasmas during a combined heating phase of ECH+NBI, using a heavy ion beam probe. The transition occurs in a timescale of a few dozen or a hundred microseconds. Radial current to induce the transition is evaluated by high temporal resolution of the heavy ion beam probe. Neoclassical dependence of radial electric field on a plasma parameter will be discussed to clarifv the nonlinearitv to allow the transition.