Mode locking from an applied stationary error field in MST

To gain a better understanding of mode locking resulting from magnetic field errors in the reversed field pinch (RFP), a stationary field error has been applied to MST to determine the locking threshold amplitude and dependence on the spatial structure of the field error. Mode locking could be robustly produced by an applied m = 1 field error, which is resonant with the core tearing modes. A dominantly m = 0 field error did not produce locking. The toroidal loop voltage Vloop was not significantly changed by the applied error field nor by the occurrence of locking.