Design of the HGVPU Undulator Vacuum Chamber for LCLS-II

A vacuum chamber has been designed and prototyped for the new Horizontal Gap Vertically Polarization Undulator (HGVPU) as part of the LCLS-II upgrade project. Numerous functional requirements for the HGVPU assembly constrained the vacuum chamber design. These constraints included spatial restrictions to achieve small magnet gaps, narrow temperature and alignment specifications, and minimization of wall erosion and pressure drop within the cooling channels. This led to the design of a 3.5-meter length, thin walled, extruded aluminium chamber with interior water cooling. FEA stress analysis was performed to ensure the chamber will not fail under vacuum and water pressure. A cooling scheme was optimized to ensure water flow is sufficient to maintain temperature without the risk of erosion and to minimize pres-sure drop across the chamber.