Particle influx studies and confinement properties in RFX-mod

The investigation on a wide range of plasma densityof the particle confinement properties will be discussed in this work for high current (Ip > 1MA) experiments at RFX-mod. To study the paricle influx from the wall, a synthetic diagnostic has been developed in RFX-mod. It simulates the H? emission and a 2-dimensional map of the particle influx has been computed. At high current and low density (n/nG <0.3), the RFP exhibits a self-organized helical regime, where the innermost resonant tearing mode grows to large amplitude. If such amplitude is sufficiently large, the original magnetic axis is replaced by a new helical axis, bringing about the single helical axis (SHAx) state. A strong effort has been developed to describe the peculiar plasma wall interaction and the consequent particle influx fromthe wall during the single helical state. Indeed plasma edge is strongly distorted by the dominant mode and a dependence of the particle influx on the associated helical ripple is present. The dynamics of the H?signals measured in different poloidal and toroidal positions have been analyzed considering the experimental plasma density, temperature and the 3D magnetic topology. Increasing the density the SHAx topology is lost and the multiple helicity state occurs: a wide spectrumof these locked resonant tearing modes produces a toroidally localized large distortion of the plasma column, named locked mode (LM). This distortion leads to a much more local power deposition on the first wall. The particle influx results localized as well. The H?synthetic diagnostic has been used to interpret both data in low and high density regimes. The average particle influx increases almost linearly with density in the range 2-6x10 19 m -3 and it shows saturation or damping at higher density, even considering the strong contribution at the LM position. Exploiting such description of the particle influx,and its dependence on the density level, a transport analysis has been carried out with the ASTRA code. A reduction of the diffusivity has been observed at low density in the plasma core, thanks to the magnetic surfaces associated to the SHAx state whereas a larger particle transport is present at the edge. At higher plasma density a better global particle confinement is found. The relative role on the particle transport of the magnetic diffusion term and of the electrostatic turbulence will be discussed.