Edge turbulence approaching the density limit in RFX-mod experiment

The boundary region of the RFX-mod reversedfield pinch experiment is strongly influenced bythe value of the electron density. With increasing density the magnetic topology in the plasmacore and in the plasma edge changes, together with the statistical properties of the edge turbulentfluctuations. Using the density normalized to the Greenwald density(n/nG), two density regimesare identified: the low density regime at n/nG<0.3-0.4, and the high density regime forn/nG>0.4-0.5, without a clear threshold between them. At low density the plasma isdominated by the(m, n)=(1,-7)magnetic mode, which gives the same shape to the magneticboundary; at higher density a strong(0, 1)mode rises. When increasingn/nG, edgefluctuationsdevelop strong non-Gaussian tails, turbulent structures become larger and their radial velocitybecome measurable with the gas puff imaging diagnostic whenn/nG>0.3-0.4. Thisphenomenology is described in detail for the two density regimes of RFX-mod.