Role of the m = 0 modes in the edge region of a reversed-field pinch during pulsed poloidal current drive

Changes in the edge profile of soft x-ray emission during pulsed poloidal current drive (PPCD) experiments are in agreement with the modifications of the plasma surface, as seen from magnetic measurements. In particular, the m=0 modes resonant at the reversal radius have been analyzed. A comparison with an m=0 island reconstruction model shows that PPCD reduces the bulging associated with the m=0 modes by shifting inward the reversal surface, where the m=0 island is located. Regarding the total m=0 amplitude, there are evidences that during PPCD, on average, it does not change significantly. Additional data coming from standard discharges support the idea that two competing phenomena act during PPCD: one is the inward shift of the reversal, which destabilizes the m=0 modes; the other one is the decrease of the m=1 fluctuations, which acts in the opposite direction. (C) 2003 American Institute of Physics.