Plasma edge cross-field transport: experiment and theory

In recent years, the basic physics picture of plasma transport in the scrape-off layers of tokamaks and stellarators has changed. This basic picture was based on slow diffusive cross-field transport competing with fast parallel transport. However, the idea of a local diffusive cross-field transport picture is not compatible with some of the experimental findings. Cross-field particle fluxes have an intermittent character. Large transport events can be responsible for a large portion of the total integrated flux. Those measurements also show the existence of long-range correlations in time and space. These correlations break down a possible separation of scales that was the base in deriving the macroscopic transport models. Structures are not limited to density fluctuations; they also appear on edge flows. The interaction between fluctuations and flows becomes one of the most important issues in the plasma edge dynamics.