22 July 2010 Liquid nitrogen pre-cooling of large infrared instrument at ESO
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Since the last decade, most of the large infrared instruments are kept at operating cryogenic temperature using mechanical cryo-coolers. Generally Gifford MacMahon Closed Cycle Coolers or Pulsed Tubes are doing this duty. These coolers are well dimensioned to keep the instrument and the detector at a sufficiently low operating temperature. Using the only cooling power provided by the steady state mechanical cryo-coolers would lead to several days for the initial cooling down. Therefore an additional cooling has to be used to allow a reasonable cooling time. The present paper describes the liquid nitrogen continuous flow cooling system developed at ESO for ISAAC. During the past years, this system has also been used successfully for a number of VLT instruments (CRIRES, HAWK-I..). After a short comparison with the more common technique using an instrument internal tank, we list in detail the various developments which have been required to get the continuous flow working in a reliable and efficient way. This paper also presents the advantages making this technology as a potential very attractive way to replace definitively mechanical coolers in most of the cases.
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J. L. Lizon, J. L. Lizon, "Liquid nitrogen pre-cooling of large infrared instrument at ESO", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77393F (22 July 2010); doi: 10.1117/12.856014; https://doi.org/10.1117/12.856014

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