This review article summarizes the recent advances in the investigation of multilayer insulation in the light of cryogenic radiation heat transfer. Brief summary for the previous investigation of multilayer insulation is first made after “Advances in Cryogenic Engineering” volumes and next some problems that are peculiar to cryogenic radiation heat transfer systems are pointed out after Tien and Cravalhos' article. Discussion is expanded to the recent study for the prediction of heat transfer rate in multilayer insulation through the introduction of the author's own investigation both experimental and of analysis. Other related investigations in this field are also introduced and discussion as to the relationship among those studies is made. Some prospective research areas in the cryogenic insulation technology are pointed out.
In order to realize a stable and continuous cooling system of superconducting magnets for magnetically levitated high speed trains, design study of the cryostat with liquid helium condenser has been performed. Boil-off helium gas inside liquid helium vessel of the cryostat is to be reliquefied by liquid helium condenser in which helium mist coolant from a external helium refrigerator is flowing.
A cryostat coupled with helium refrigerator has been constructed and tested in order to establish an on-board refrigeration system of superconducting magnets for magnetically levitated high speed trains. The cryostat (1975mm in length×745mm in hight×185mm in width, and 320kg in weight) is composed of a liquid helium vessel in which a coil and a liquid helium condenser are mounted, two layers of radiation shields and an outer vessel. A modified Sumitomo's 4l/h helium liquefier is used as a refrigerator which provides its helium coolant to two radiation shields and to the liquid helium condenser, simultaneously. The helium mist coolant in the condenser suppresses an increase of gas phase pressure inside the liquid helium vessel. This clearly indicates the condensation of evaporated helium gas in the vessel. All the system showed smooth, stable operation throughout the experiments. A series of tests provide us useful design data for the on-board refrigeration system.