Boundary plasma response in RFX-mod to 3D magnetic field perturbations

Highlights: • Poloidal measurements of edge plasma pressure and floating potential. • Analysis of edge plasma measurements in the helical angle frame. • Effective local deformation of magnetic surfaces in the edge. • Edge magnetic topology in RFP depends from m=1 stochastic layer and m=0 islands. • Plasma response to a monochromatic MP depends on the toroidally coupled sidebands. - Abstract: The edge of the RFX-mod (R = 2 m, a = 0.46 m) Reversed Field Pinch device is characterized by weak magnetic chaos affecting ion and electron diffusion. Edge particle transport is strongly influenced by a toroidal and poloidal asymmetry caused by magnetic islands and an ambipolar radial electric field ensures local neutrality. At higher plasma current (I_ϕ>1MA) a spontaneous resonant dominant mode m/n = 1/7, slowly rotating, develops in the inner region. The edge electron pressure P_e and floating potential V_f show a shape of the Plasma Wall Interaction (PWI) with the same toroidal periodicity, which follows the edge local ideal magnetic displacement Δ_1,7. Detailed measurements along the poloidal direction of P_e and V_f have been undertaken newly, their time behavior present respect to Δ_1,7 a time lag, which depends on the poloidal angle θ. The mode analysis in terms of helical angle reveals a role of the 0/7 mode in determining a poloidal phase lag respect to Δ_1,7 of P_e and V_f. Since the 0/7 is the largest toroidal sideband of the 1/7 mode, this work suggests a role of toroidal coupling in determining the plasma response to a MP.