Upgrade of the spoke test cavity station

Originally the spoke test cavity cryostat was designed to test exclusively SSR1 cavities. The goal of this upgrade is to extend this capability to SSR2 cavities, and to the low and high beta 650 MHz cavities. These cavities are the last elements of the superconducting linac architecture which is the main component of the Proton Improvement Plan-II (PIP-II) at Fermilab. The size of SSR2 and 650 MHz cavities being much bigger than SSR1, extensions of the vacuum vessel and of all the cryogenic lines have been necessary. Mechanical, thermal and cryogenic analyses have been performed to ensure proper operation. This paper summarizes the design choices which have been made by describing the main elements of this upgrade and the interface between cryogenic lines and cavities.