The principle of pumping mechanism and basic construction for the cryopump cooled by a small refrigerator are described. Also some applications of the cryopump are described. Two-staged Gifford-McMahon cycle or modified Solvay cycle refrigerator are commonly used for the cryopump. The first stage cold station cools a baffle and a radiation shield which condenses water vapour and blocks thermal radiation to the cryopanel. The cryopanel cooled by the second stage cold station condenses most gases except neon, hydrogen and helium which are adsorbed by charcoal attached to the cryopanel. Pumping speed for a cryopanel is led from the statistical mechanics. An operating procedure based upon a typical cryopump system is also described.
An enormous number of papers on high Tc superconductors have been reported since the discovery of Ba-La-Cu-O superconductor in 1986. It becomes difficult for many researchers to read out the papers related to their field. In this article we report the explanation of numerical database for high-Tc superconductors “SUPERCON” which has been constructed in NRIM. The crystal structures of high-Tc superconductors are classified using the common name used in many papers. The references are represented by a newly developed reference number. Numerical data on superconducting properties, Hall coefficient, thermal conductivity, thermoelectric power and specific heat are collected from the published papers. Metadata and the usage of “SUPERCON” are described.
Fundamental techniques of superfluid cooling of superconducting magnets and electronic apparatuses are exemplified by an AC magnet. Superfluid helium, as a cryogen for magnets, has excellent properties such as superfluidity and super-thermal conductivity. Despite these properties, its heat transport capacity is restricted by narrow cooling channel configurations of a magnet winding and by the critical heat flux for a surface of a superconducting wire. To obtain the maximum heat transport and maximum critical heat flux, the optimum operational temperature should be between 1.8 and 1.9K. Also mentioned is the heat transfer to superfluid helium under transient state, where one can obtain a critical heat flux that is higher than that under the steady state but with a lifetime less than a one millisecond.