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Handbook of High Temperature Superconductor Electronics Part 13

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Tham khảo tài liệu 'handbook of high temperature superconductor electronics part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 12 Cryocoolers and High-Tc Devices Ray Radebaugh National Institute of Standards and Technology Boulder Colorado U.S.A. 12.1 INTRODUCTION 12.1.1 Cooling Requirements for High-Tc Superconducting Electronic Devices A long-range goal in the study of superconductivity is to find a new material with a superconducting transition temperature Tc significantly above room temperature so that there would be no need to cool the superconductor. Such a breakthrough would be of profound significance because it would then free superconductivity of the problems imposed upon it by the need for cooling. Operating temperatures of less than about two-thirds of the transition temperature are required to significantly reduce the temperature dependence of the critical current and to achieve satisfactory performance of superconductors in practical applications. At present temperatures below 80 K are needed for practical use of even the highest-temperature superconductors. Although liquid nitrogen is often used for laboratory studies of high-Tc devices it is rarely satisfactory for commercial applications. This dependence on cryocooling then adds another set of problems that must be overcome in moving a superconducting device into the marketplace. In terms of any marketable product the superconducting device and the cryocooler must be considered an inseparable pair. There are many problems associated with cryocooling the superconductor and it is these problems that often prevent the su Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. perconductor from making it into the marketplace. Studies to improve the performance of superconducting devices and systems should be coupled with studies to improve the performance and lower the cost of cryocoolers. The purpose of this chapter is to discuss the various methods available for cooling high-Tc superconducting electronic devices. The differing requirements of various superconducting devices often lead to different cooling methods being .