Unwanted process defects occur during laser deep penetration welding. The formation mechanisms of the main process defects like spatters and pores are not completely identified yet. Several methods like beam oscillation or laser power modulation are known to help reducing the occurrence of defects. These methods change the temporal energy input. It can be assumed that also beam shaping influences the energy input into the keyhole and has the potential to influence process defects as well. Due to the adapted energy input keyhole instabilities, that are assumed to influence the formation of the defects, can be avoided. A newly developed multi-focus beam shaping optic that creates multiple beam waists in axial direction is used in this work. The additional areas with increased intensities are used to modify the energy input in the keyhole in order to explain the mechanism of spatter formation and evaluate the potential of the axial beam shaping for defect suppression during laser deep penetration welding. It is found that the number of spatters can be reduced when the middle sections of the keyhole are illuminated with a high intensity. It can be concluded that spatters can be reduced when a keyhole collapse is avoided and a high enough energy input is guaranteed in the upper keyhole sections.