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Cryogenics is the science of making and maintaining low temperatures, studying the properties of materials and systems at low temperatures, and safely utilizing low temperatures for applications such as superconductivity, electronics, and medicine. At the University of Wisconsin - Madison we have been at the forefront of cryogenic developments supporting superconducting applications, and exploring new refrigeration cycles. We have measured unique modes of normal zone propagation in superconductors carrying 60 kA at 1.8 K and 4 tesla, and have developed state-of-the art quench detection systems for multiple-coupled superconducting coils. Our cooling system for tests related to Superconducting Magnetic Energy Storage (SMES) provides 35 watts of refrigeration at 1.8 K. Since the discovery of High Temperature Superconductivity (HTS), we have been exploring the practical limitations of current leads utilizing HTS elements, providing guidelines for their design, and have patented a twin-cold-finger cryocooler to manage their thermal loads. Our recent interests involve characterizing the thermal stability of HTS conductors, especially the coated conductor configuration of YBCO tapes. Thermal models are being combined with experimental measurements to investigate the limiting modes of operation for these 2nd generation HTS conductors. To accommodate HTS applications that may be cooled in a bath of liquid nitrogen, we are studying nucleate boiling phenomena in very narrow channels with the use of fiber-optic imaging in the cryogenic environment.
Refrigeration at cryogenic temperatures has evolved from the very large and cumbersome systems developed before 1960 to small, high efficiency refrigerators called cryocoolers. The Cryogenics group at the University of Wisconsin - Madison houses cutting-edge expertise in the development of Pulse-Tube, Reverse-Brayton, Joule-Thomson, and various hybrid cryocoolers. Our activities draw from fundamental principles of heat transfer, thermodynamics, fluid mechanics, and materials science, and utilize generous doses of innovation and experience. Through a combination of experiments and numerical modeling we have developed a broad understanding of both low and high- frequency Pulse Tube refrigerators and are developing hardware examples for military, electronics, and superconducting electric power applications. Combinations of regenerative and recuperative cryocooler cycles are being explored to provide compact, high efficiency coolers for superconducting and cold-electronics applications. We are exploring the use of shape-memory-alloys at cryogenic temperatures to improve the reliability of Joule-Thomson cryocoolers, and to reduce vibrations in a variety of cryocooler applications.
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