Many cryopumps have been used to produce clean vacuum for LSI manufacturing equipment and experimental equipment of fusion reactor, etc. In this paper, the pumping principle of cryopump is described. A structure and operation of the cryopump with a closed-cycle refrigerator are also described. Recently, some types of cryopumps which are just suitable to the function of particular purposes have been developed. For examples of these cryopumps, cryopump for ultra high vacuum, cryopump with high pumping speed and cryopump for sputtering equipment are also introduced.
Mechanical properties of SUS 321 (18 Cr-9 Ni-Ti steel) and 347 (19 Cr-9 Ni-Nb steel) aged at 700°C×75hr were studied at the temperatures below the room temperature, especially at liquid helium temperature. Cr rich carbides, M23C6, precipitated at grain boundaries in the both steels during aging whether the both were stabilized at 900°C beforehand or not. The distributions of grain boundary precipitates, however, were different. The aged SUS 321 showed both connected precipitates along grain boundaries and fine TiC scattered uniformly. On the other hand the aged SUS 347 presented isolated ones along boundaries as well fine Nb (CN) distributed uniformly. The degradation of tensile properties at 4K was small but that of fracture toughness was very large. The degree of degradation of SUS 347 was much smaller than that of SUS 321. Moreover 4K JIC specimens of SUS 347 fractured transgranularly while those of SUS 321 did intergranularly. The results make it clear that the degradation of 4K fracture toughness due to aging could be suppressed by controling morphology of precipitates and that niobium addition is effective to make the morphology advantageous.
In order to study stability and A.C. losses in A.C. superconducting coils, the authors have developed two 50kVA class coils and operated it at 50Hz. These coils were made of an ultra-fine multifilamentary superconducting 42-strand cable. Nevertheless the conductor has CuNi matrix without Cu, one coil could be operated continuously at nearly 50kVA. The coil was quenched at 173A r.m.s., whose peak value was about 87% of the short sample D. C. critical current. Maximum field was 1.59T. To prevent wire motions and retain helium ventilation, the cable was embedded in grooves on coil formers made by fiber reinforced plastic. The apparent normal zone propagation velocity is much larger than the calculated adiabatic propagation velocity.