Plasma Confinement Characteristics in Heliotron J—Spontaneous Change of Plasma Confinement State

Spontaneous transition of the plasma confinement mode was observed in the helical-axis heliotron device Heliotron J for three different plasma heating schemes, i.e. ECH-only, NBI-only and the combination of ECH and NBI. The transition seems to occur above a certain critical density. In addition to the confinement transition, a spontaneous shift of the hitting position of the divertor plasma flux on the wall was observed. This shift could be related with the change of the edge field topology caused by non-inductive toroidal currents.