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Challenges in the Cryogenic Cooling of the 3.3 Giga Pixel detector array of the Large Synoptic Survey Telescope for deployment in Chile in 2020
Keywords: Telescope, Large, Compressor
In late 2009 the Stanford Linear Accelerator Center asked if MMR could provide cooling of the detector array of the Large Synoptic Survey Telescope – a project of the Department of Energy. This would require about 600W of cooling at 140K. This was many, many times more than anything we manufactured, as indeed MMR stands for Micro Miniature Refrigerators, which are tiny, microscope slide-size cryogenic refrigerators that provide milliwatts of cooling using the Joule Thomson effect. While MMR had sourced other closed cycle coolers that provide cooling to 80K for High Purity Germanium detectors that monitor nuclear fallout, but they have a refrigeration capacity less than 10 Watts at 100K, much too small for this project. This “interesting challenge” spawned a fruitful collaboration. The final design required six separate compressor modules, each of which was larger than any of our earlier coolers, and each would cool one sixth of the detector cold plate. Calculations predicted capacity to lift 90 to 100 Watts at 140K per module. The prototypes came close, but revealed another problem, that six compressors, condensers and heat exchangers would hold an enormous amount of flammable refrigerant. Fortunately an MMR senior scientist learned of newly synthesized refrigerants from colleagues which enabled the performance needed without explosion hazard. The physical implementation is a final great challenge that will be discussed in the presentation.
William A. Little, PhD,
MMR Technologies, Inc.
San Jose , CA

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