MACROSCOPIC BEHAVIOR AND DISCRETE DYNAMO IN HIGH-THETA REVERSED-FIELDPINCH DISCHARGES

The magnetohydrodynamic (MHD) activity and the discrete dynamo in high -THETA reversed-field pinch (RFP) discharges are studied through compa risons with those in normal-THETA RFP discharges, where THETA = B(thet a)(a)/[B(z)] is the pinch parameter. In high-THETA RFP discharges, the mode coupling of m = 1 is enhanced by the high magnetic shear configu ration, and the MHD activity is more turbulent as compared with that i n normal-THETA RFP discharges. Furthermore, the discrete increase of t he 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 t he discrete dynamo does not play an essential role in the RFP dynamo.