Interface transport barriers in magnetized plasmas

Abstract

We address the formation of Interface Transport Barriers using a generic turbulent transport model, reduced to 2D, and used to investigate interchange turbulence in magnetized plasmas. The generation of a transport barrier at the edge-scrape off layer (SOL) plasma interface is governed by a zonation regime in the edge region with closed-field lines. The barrier is triggered by a gap in the turbulent spectrum between zero, the zonal flow wave vector, and the wave vector of the spectrum maximum. This gap is controlled by the energy injection wave vector of the interchange instability and the Rhine scale that bounds the inverse cascade. Increasing the magnitude of the turbulence drive at a given gap reinforces the transport barrier. In the interface transport barrier regime, edge relaxation bursts of turbulence regenerate the zonal flows that are eroded by damping processes such as collisions. The duration of the quiescent phase between the quasi-periodic relaxation events is then governed by the ion collision frequency. Such an interface transport barrier can play the role of a seed barrier prior to a full bifurcation to improved confinement.