Multi-scale physics and transport barriers in fusion plasmas

Abstract

Both tokamaks and stellarators develop edge bifurcations with basically similar properties, demonstrating the ubiquitous character of the low to high (L–H) transition in fusion plasmas. Experiments have shown that the paradigm of turbulent control by sheared flows should include both mean and oscillating sheared flows. Recent experimental findings point out the possible role of fluctuating sheared flows (zonal flows) as a trigger mechanism of edge transport barriers. This is in line with the expectation that multi-scale interactions are a crucial ingredient of the L–H transition dynamics. These observations provide a guideline for further developments in plasma diagnostics and transport studies of plasma bifurcations.