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 m50 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 m50 modes; the other one is the decrease of the m51 fluctuations, which acts in the opposite direction. © 2003 American Institute of Physics.