Developments in advanced and energy saving thermal isolations for cryogenic applications

Abstract

Abstract. The cooling power consumption in large scale superconducting systems is huge and cryogenic devices used in space applications often require an extremely long cryogen holding time. To economically maintain the device at its operating temperature and minimize the refrigeration losses, high performance of thermal isolation is essential. The radiation from warm surrounding surfaces and conducting heat leaks through supports and penetrations are the dominant heat loads to the cold mass under vacuum condition. The advanced developments in various cryogenic applications to successfully reduce the heat loads through radiation and conduction are briefly and systematically discussed and evaluated in this review paper. These include: (1) thermal Insulation for different applications (foams, perlites, glass bubbles, aerogel and MLI), (2) sophisticated low-heat-leak support (cryogenic tension straps, trolley bars and posts with dedicated thermal intercepts), and (3) novel cryogenic heat switches. IntroductionKeeping temperatures of a large scale cold mass within a few kelvin of absolute zero is a great challenge. Many superconductivity projects have cold masses kilometers in length or huge complex machines, such as CERN, RHIC, Fermilab, CEBAF, DESY and ITER [1][2][3]. The high Tc superconducting applications and other usages with LO 2 , LN 2 and LH 2 present different requirements.For example, requirements for the LHC magnets distributed in a tunnel of 27 km can be summarized in terms of heat load per meter as follows [3]: total leak from 290 K vacuum vessel to 80 K shield is 4.26 W (3.76 W by MLI, 0.68 W by support) and from the 80 K shield to the cold mass is 0.18 W (0.09 W by MLI and 0.09 W by supports). Obviously, the design and implementation of high thermal efficient supports is about equally crucial to the contribution of high performance MLI.This review paper will cover energy saving cryogenic transfer lines and then discuss the sophisticated support structures in large magnets, SRF cavities, and detectors. The merit of traditional powder type insulation and newly developed aerogels insulation are compared [4]. The performance, materials and design combinations of various super-insulations or multilayer insulation (MLI) are summarized. Special attention is then given to the tests and improvements of MLI with penetrations [5]. Finally, novel cryogenic switches for thermal management are also mentioned.

Design, configuration, and thermal optimization of advanced cryostats

“…Cryostats come in all shapes and sizes, ranging from palm-sized devices to massive superconducting accelerators and fusion Tokamaks, weighing hundreds of tons and spanning tens of kilometers. As extensively discussed in references [1][2], researchers are leveraging their extensive technical experience with existing cryostats to develop guidelines for addressing the challenges of further optimizing and expanding the use of these critical systems. A brief review of advanced cryostat designs currently in use is provided.…”