The ELT cryogenic infrastructure

The European Southern Observatory (ESO) is at present constructing the Extremely Large Telescope (ELT), a 40-m class astronomical telescope on top of the 3046 m high mountain Cerro Armazones in the central part of Chile’s Atacama Desert. In combination with its powerful facility instruments, it will be the largest optical/near-infrared telescope in the world, also known as the biggest eye on the sky. The instrument roadmap lists up to eight scientific instruments, whereof the first light instruments were already completing their final design phase. Nowadays massive instruments, each weighing about 20 to 40 tons, are requiring powerful cryogenic systems for cooling the cold mass of several tons of each individual instrument. <br/> <br clear="all"/> The paper outlines the cryogenic requirements defined by the ELT instrument suite and describes concept and design of the cryogenic infrastructure. A centralized and fully automated system combining open loop Liquid Nitrogen cooling in combination with low-vibration mechanical cryo-coolers is the baseline for providing the required cooling capacity and temperature levels as low as 4 Kelvin. Project status and timeline are presented.