Role of edge magnetic shear on the limiter H-mode transition of the JIPP T-IIU tokamak

In a circular cross-section plasma bounded by a limiter, the H-mode transition is triggered by rapid ramp-down in a plasma current during additional heating, even in the case that the edge electron temperature decays gradually prior to the transition. This result suggests that the enhancement of a magnetic shear near the plasma edge by the ramp-down plays a crucial role on the transition, and that the transition in a limiter-bounded plasma is essentially governed by the current density profile near the edge. (author)