[en] A m=1, helically displaced current channel was identified in the ASDEX plasma interior during m=2 mode activity. This was achieved by means of simultaneous data obtained from a new gradient sensitive schlieren diagnostic and B_P measurements. They clearly show a rotational-transform-dependent coupling mechanism between the driver m=1 current helix and the m=2 perturbation of the bulk current surrounding it. The mechanism is of central importance for the development of the instability and for the theoretical understanding of mode coupling, mode locking and other varieties of mode structures in plasma. (orig.)