Investigation on the relation between edge electric radial field asymmetries in RFX-mod and Greenwald limit

In all major confinement devices (tokamaks, stellarators, spheromaks and reversedfield pinches - RFP), a density limit has been found (Greenwald and Sudo limits). Results summarized in [1] show that in the RFP high density does not cause a disruption, but a sequence of phenomena leading to the disappearance of quasisingle helicity (QSH)/Single Helical Axis (SHAx) [2], density increase, radiation condensation and fast resistive decay of the plasma current. In this paper we discuss the coherence of the magnetic ripple and its effect on test particle motion, and the impact of edge turbulent transport through "blobs". The competition between collisional and turbulent transport may be envisaged to rule the observed density limit.