Transport mechanisms in the outer region of RFX-mod

The transport processes taking place in the outer region of fusion-relevant magnetically confined plasmas are generally believed to be driven by the fluctuating electric field associated to plasma microturbulence. The edge plasma of RFX-mod, a large reversed field pinch (RFP) toroidal device, shares many peculiar characteristics of other configurations. The edge turbulence exhibits an intermittent behaviour, associated with blobs, coherent eddies and structures emerging form the turbulent background. Despite the crucial role in the improved confinement regimes of the interaction between the generation/dissipation of the flow and the creation/destruction of turbulent structures, its description is far from being completely understood. RFX-mod is equipped with a full set of edge diagnostic systems with sub-microsecond time resolution: the Gas Puffing Imaging diagnostic which gives great details of the structures and of their dynamics; the Integrated System of Internal Sensors, a distributed system of in-vessel magnetic and electrostatic probes, which can follow the structures in their motion and relate them to large scale instabilities; an insertable 'U-probe' which simultaneously measures local magnetic field, current density, plasma pressure, E x B flow and turbulent particle flux; a 'Gundestrup probe' which provides direct measurements of both parallel and perpendicular flow. Very recently new Thomson scattering and thermal Helium beam spectroscopy diagnostics for measurement of edge electron density and temperature profiles have been put into operation. The paper presents the new insights achieved starting from the obtained measurements: the properties of the structures in terms of pressure, flow and current density; an estimation of the diffusivity associated to the coherent structures, found to decrease with increasing n/n_Greenwald between 0.1 < n/n_G < 0.35 with a tendency to saturate at higher values; the analysis of turbulent momentum fluxes, described in terms of the Maxwell and Reynolds stress terms of momentum transport equation, where the Reynolds stress has been found to dominate the process over the Maxwell stress for at least a factor five. (author)