Transition from divertor to limiter configuration and associated transient plasma oscillation in Heliotron J

A transition from a divertor configuration to a limiter configuration and associated transient plasma oscillation were observed in configurations whose confinement region expanded with the codirected plasma current in the Heliotron J device. The transition was associated with the edge plasma profile such as electron density and temperature, and the change in the particle flux on the divertor probe was qualitatively consistent with the magnetic field line tracing calculation result, including the effect of the plasma current. During the transition, a spontaneous oscillation with a toroidal mode structure of n = 1 was observed at approximately 2 kHz, accompanied by an edge plasma response with a synchronized divertor footprint shift. This suggests that the transition to the limiter configuration was coupled with transient oscillatory responses. The study shows that the plasma current alters the edge magnetic field structure, and the edge plasma oscillates as a transient response.