Plasma-wall interaction and locked modes in the toroidal pinch experiment TPE-RX reversed-field pinch

The MHD instabilities that sustain the reversed-field pinch (RFP) configuration tend to phase-lock together and also to wall-lock, forming a bulging of the plasma column, called "locked mode". This phenomenon is of particular interest, since the locked mode causes a larger plasma resistivity, plasma cooling. and, in some cases, anomalous discharge termination. Up to now, studies of the locked mode have been focused on in = I modes (being in the poloidal mode number). In this Letter we show that in = 0 modes also play a role, based on the cross-check between magnetic spectra and toroidally resolved D, array measurements.