In the past few years, most DNA constructions have been desided through the project of GENOMICS or civilian companies. But these constructions were only “Drawings for protains.” To develop medical science or to new medicines, the actual construction of all protains must be cleared. High-magnetic field NMR, Nuclear Magnetic Resonance, is the most effective way to analize these protains. Along with the “TROSY” method, a magnetic field required to achieve 25.85T (1.1GHz) to clear all protain constructions. Depending on these requiments, recent development of the magnet forword to achieve heiher magnetic field. On the other hand, critical current: Ic of superconductiving wire almost aproechies its critical value, which depends on material property. The only way to have a heigh magnetic field is to decrease its operating temperature. This paper shows the recent development of cooling techniques below 4.2K, using superfluid helium, including the subcooled helium method, on NMR cryostat.
The LHC project is in progress at CERN. The LHC accelerator, whose beam energy is 7TeV, consists of more than 2, 000main superconducting magnets. Almost all the magnets are to be operated at 1.9K pressurized He II cooling because of the high magnetic field. The cooling system consists of 8 refrigerator units with a large equivalent capacity of 18kW at 4.5K. Each unit covers to cool the aligned magnets along a distance of 3.3km long. In order to obtain 1.9K pressurized He II with better efficiency, 8 cold compressor units will be installed into the 8 refrigeration systems. The necessary cooling of the magnets is obtained with pipe-shaped heat exchangers embedded in magnet iron yokes. The minimum cooling unit of the magnets is composed with the 6main dipole and 2main quadrupole magnets. The unit length is 106m. This paper will describe the outline of the He II refrigeration system.