On the origin of "intermittency" in the scrape-off layer of linear magnetic confinement devices

The goal of this article is to show that the "intermittent" convective transport in the scrape-off layer (SOL) of linear magnetic confinement plasmas actually takes place periodically. This is reflected in several features that are unveiled in this article. It is found that the distribution of the time between high-amplitude bursts, selected above a given threshold, has a central frequency in the SOL. Moreover, this distribution is found similar to the one taken inside the main plasma column as the threshold is reduced, suggesting links between the SOL and the main plasma column. The power spectrum of the radial flux is determined, indicating the presence of a coherent peak that accounts for about 50% of the transport. Using two probes that are poloidally and radially separated, it is shown that a burst in the SOL is correlated to a wave packet inside the main plasma column. The relation between the two distant regions is thus assured by avaloids that are nonlocal structures in nature as they have velocities much higher than the background. (C) 2003 American Institute of Physics