Internal Transport Barrier and Bifurcation Phenomena in Stellarators

Bifurcation phenomena with confinement improvement in toroidal plasmas are briefly reviewed. After a general discussion of the formation mechanisms of improved confinement modes, the electron internal transport barrier commonly observed in stellarators is chosen here as the main subject with focus on the following aspects: the bifurcation property, the scenario of bifurcation with confinement improvement, and the confinement features. Several works to investigate the relationship between rational surfaces and barrier formation are introduced as examples to show the relation between magnetic topology and the bifurcation property. The roles of stellarators, which have a wide variety of configurations, for understanding bifurcation phenomena are discussed.