An equilibrium model for RFP plasmas in the presence of resonant tearing modes with an application to particle and heat transport

The equilibrium of a finite-beta cylindrical RFP plasma in the presence of saturated-amplitude tearing modes is investigated. The singularities arising from the perturbative analysis of the MHD force balance equation JxB=grad(p) are resolved through a proper regularization of the cylindrical symmetric component of the pressure and parallel current density profiles, by setting to zero their gradient at the modes rational surfaces. An equilibrium model, which satisfies the regularization rule at the various rational surfaces, is developed. The comparison with the experimental data from the Reversed Field eXperiment (RFX) gives encouraging results. The model provides an easy tool to extrapolate the magnetic data, ordinarily measured only at the plasma edge, inside the plasma. As an application, we present the computation of the particle and heat stochastic diffusion coefficient from the reconstructed magnetic field profile.