Analysis of phase locking of tearing modes in reversed field pinch plasmas

The reversed field pinch magnetohydrodynamics (MHD) is characterized by a b road spectrum of interacting resistive tearing modes with poloidal mode num ber mainly m = 0,1. According to the nonlinear coupling theory, the modes p hase lock together if their amplitudes exceed a critical value. In the Reve rsed Field Pinch Experiment (RFX) [L. Fellin , Fusion Eng. Des. 25, 315 (19 95)] they are always locked in phase, determining a global nonaxisymmetric magnetic perturbation. In this work a detailed experimental characterizatio n of the magnetic perturbation is presented. The typical toroidal profiles and spectra, for both the m=0 and the m = 1 components, are shown. In parti cular the phase relationship under locking conditions between the interacti ng m = 0,1 modes is investigated and compared with the theoretical predicti ons. The results of three-dimensional (3D) MHD numerical simulations are al so discussed. (C) 2001 American Institute of Physics.