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5 July 2000 Cryo design for the VLTI MIDI instrument
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The paper describes the cryogenic design of the 8 - 12 micrometers beamcombiner instrument MIDI for the VLTI. Because the instrument is very sensitive at the whole thermal wavelength region, all optics and mechanics inside the dewar have to be cooled to temperatures at 40 K. The main contribution to the heat load is the radiation. We propose to use one liquid Nitrogen cooled radiation shield and a second shield cooled by the first stage of a closed cycle cooler with a refrigeration capacity of 35 W at 50 K and 1.5 W at 4.2 K. The main problems by using a closed cycle cooler are the vibrations which can disturb the interferometric measurements. We measured the vibrations during cooler operation and checked different vibration isolation possibilities.
© (2000) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ralf-Rainer Rohloff, Werner Laun, Uwe Graser, Norbert Ortlieb, and Matthias Lebong "Cryo design for the VLTI MIDI instrument", Proc. SPIE 4006, Interferometry in Optical Astronomy, (5 July 2000); doi: 10.1117/12.390219;

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