Thanks to the installation of four APPLE X helical undulators, the SASE3 soft X-ray beamline at European XFEL will provide to the experimental stations the polarization control of the X-rays. The helical undulators are located downstream with respect to the already existing planar undulators. The design of the magnetic active parts and of the helical undulator support structure requires a new design of the vacuum chamber and its alignment system. This contribution describes the mechanical design, production process, UHV qualification process and alignment of the vacuum chamber.
