Power deposition in the wall of the helical undulator of the ILC positron source

The positron source of the International Linear Collider is based on a superconducting helical undulator passed by the high-energy electron beam to generate photons which hit a conversion target. Since the photons are circularly polarized the resulting positron beam is polarized. At ILC250 (E$_{cm}$=250 GeV), the full active length of 231 m (320 m total length) is needed to produce the required number of positrons. To keep the power deposition in the undulator walls below the acceptable limit of 1 W/m, masks must be inserted. The mask design requires a detailed study of the power deposition in the walls. The results of this study are presented taking into account errors in the undulator magnetic field and period as well as misalignment of the electron beam.