Turbulence, transport and their relation with the magnetic boundary in the RFX-mod device

The outer region of Reversed Field Pinch (RFP) devices is found to share many characteristics with other magnetic configurations. Such similarities regard for instance the particle transport, dominated by electrostatic turbulence [1], the existence of blobs and intermittent structures [2, 3] and momentum transport which is found to be regulated through the electrostatic contribution to the Reynolds stress [4]. Apart from this, RFPs exhibit also peculiar characteristics due to its magnetic topology. In particular the edge region is characterized by a toroidally localized distortion of the outermost well conserved magnetic surfaces due to phase and wall locking of m=1 modes, and by the presence of chains of m=0 islands located at the reversal surface. Aim of the present paper is to analyze how such peculiarities influence energy and particle transport in the RFX-mod device, describing the confinement properties of the most external region where strong density and temperature gradients develop. The investigation of edge particle and energy transport is inferred from local measurements, with a special attention devoted to their dependency on global toroidal asymmetry and on local magnetic topology. Transport features will be addressed both by analyzing the profiles of the main plasma parameters (density, temperature, perpendicular flow and wE×B) and by investigating how profile modifications influence micro-instabilities, such as blobs dimension and dynamics, and local turbulence characteristics. An evaluation of c and D coefficients will presented. References [1] V.Antoni et al., Plasma Phys. Contr. Fusion 47, B13 (2005) [2] M. Spolaore et al, Phys. Rev. Lett., 93, 215003 (2004) [3] G.Serianni et al., Plasma Phys. Contr. Fusion, 49, 2075 (2007) [4] N. Vianello et al., Phys. Rev. Lett., 94, 135001 (2005)