Comparison of edge plasma behavior at different poloidal positions in Heliotron J

Abstract The edge plasma profile (the ion-saturation current profile) and its time evolution at three different positions of the field topology (near inboard-X, outboard-O and outboard-X points) are discussed focusing on the spontaneous transition to an improved mode in Heliotron J ECH-plasma. For all three positions it is found that the plasma profile becomes steeper as progress of the transition. In the early phase of the transition, however, the different time response is observed between the profiles near X- and O-points.