Macroscopic behavior and discrete dynamo in high-Θ reversed-field pinch discharges

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Abstract
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)/〈Bz〉 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.