Study of the scaling of magnetic fluctuations in the RFX reversed field pinch

The scaling of magnetic fluctuations with the Lundquist number (S) is studied in the RFX reversed field pinch (RFP) device for different operational regimes. For the first time in a RFP experiment a complete set of diagnostics to measure all the quantities needed to estimate S is available. Due to the high plasma currents (up to 1.1 MA) obtained in RFX, a broad range of S values is available for scaling. The results are compared with numerical MHD simulations (SPECYL code) providing a reasonable agreement (?_exp = -0.18±0.02, ?_SPECYL = -0.22). The modification to the expected scaling law due to viscous effects is also discussed. We also perform a comparison of the amplitude of magnetic fluctuations in discharges with different characteristics: standard, pulsed poloidal current drive (PPCD), quasi single helicity and rotating locked mode induced by an external rotating toroidal field modulation. A reduced level of fluctuations is obtained during PPCD operations, although the dependence on S is the same. Concerning confinement time, at fixed I/N?3×10^14 Am, a favourable scaling with S is found. Its interpretation in terms of the simple Rechester-Rosenbluth model is briefly discussed.