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The magnetohydrodynamic (MHD) activity and the discrete dynamo in high-Θ reversed-field pinch (RFP) discharges are studied through comparisons with those in normal-Θ RFP discharges, where Θ=Bθ(a)/ is the pinch parameter. In high-Θ RFP discharges, the mode coupling of m=1 is enhanced by the high magnetic shear configuration, and the MHD activity is more turbulent as compared with that in normal-Θ RFP discharges. Furthermore, the discrete increase of the toroidal magnetic flux is obviously observable. The increase of the toroidal magnetic flux generated by the discrete dynamo, which has an asymmetric structure in the toroidal direction, is only 1%–2% of the whole toroidal magnetic flux. The experimental results indicate that the discrete dynamo does not play an essential role in the RFP dynamo. [ABSTRACT FROM AUTHOR]

A rapid growth of magnetic fluctuations resulting from the m=1 and m=2 modes and succeeding stop of rotation of these modes have been found as the precursor phenomena of current termination in the STP-3(M) [Trans. Inst. Elec. Eng. Jpn. 107-B, 469 (1987)] reversed field pinch. By deepening the field reversal at the wall, these precursors disappear and the current duration becomes much longer. It is found that sudden current termination is caused by a rapid growth of resistive tearing modes mainly because of nonlinear coupling of the m=1 mode. [ABSTRACT FROM AUTHOR]