Generation of Intermittent Turbulent Events at the Transition from Closed to Open Field Lines in a Toroidal Plasma

Turbulent transport at the transition from closed to open field lines has been investigated in the stellarator experiment TJ-K. It is found that drift-wave turbulence in the confined region is responsible for the generation of intermittent structures (so-called blobs) in the unconfined region. There the character of turbulence changes and a decoupling of density and potential fluctuations is observed. The poloidal propagation of the intermittent events can be understood in the framework of background flows caused by gradients in the equilibrium plasma pressure and potential profiles.