The Universitäts-Sternwarte M¨unchen (USM) was responsible for the procurement of a big Liquid Nitrogen (LN2) continuous-flow test cryostat, equipped with a 1600 mm diameter optical bench. This cryostat is planned to perform cryogenic tests of the two large cryogenic mechanisms of the MICADO instrument, the Main Selection Mechanism (MSM) and Central Wheel Mechanism (CWM), and of some of the instrument cold optics (COI) modules. The Big Test Cryostat was delivered at the end of 2021, and is currently installed at the Max Planck Institute for Extraterrestrial Physics (MPE) laboratories. In this paper we present the design, specifications and measured cold performances of the cryostat. We also provide an overview of the tests planned inside the cryostat, which will start at the beginning of 2024 and will run until beginning of 2026, when the mechanisms and the cold optics modules will be finally integrated inside the MICADO Instrument Cryostat.
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