A bifurcative behavior of the divertor and edge plasma with self-sustained oscillations has been observed in the JET tokamak. Two plasma states are observed with high and low divertor densities. The oscillations between these two states are observed only within a certain core plasma density range and for input powers above a threshold. The change of divertor state has sizable effects on the main plasma leading to inverted density profiles and a clamping of the edge temperature which adversely influences the access to the $H$-mode regime.

• Received 18 December 1998

DOI:https://doi.org/10.1103/PhysRevLett.83.3657