The design of the cryostat for ELT/METIS

Abstract

We present the current design status of the cryostat of the Mid-infrared ELT Imager and Spectrograph (METIS) instrument to be operated at ESO’s Extremely Large Telescope (ELT). The cryostat provides the cold optics of the instrument with the required cryo-vacuum environment. The radiation shields of the cryostat are cooled with liquid nitrogen and the cold optics is cooled via pulse-tube coolers down to temperatures around 35 K. The cold-warm interface is provided with G10 blades that build together with the top part of the cryostat vessel the structural interface to the cold optics, the warm support structure and the warm calibration source. The cryostat development is currently in its final design phase which is planned to conclude in summer 2022. We present in this paper the current design status, the key design considerations and the cooling concept.