Natural gas is generally classified in two categories; the flamable gas and the nonflamable gas. Methane, Ethane etc., which belong to the former, are the main constituents of the socalled natural gas, while the helium belongs to the latter. First, the place of mines and the amounts of production are described for the flamable gas. Secondly, the following items of helium gas are described; the location of mines, the amounts of production, the recovery and the probable reserves and thirdly, the recent world trend in the field of natural gas is discussed.
One of key factors of cryogenic systems is a heat transfer from room temperature. In some cases a heat transfer by radiation is dominant. A general calculation for heat transfer by radiation is given in this paper. Assumtion used is that all surfaces are of diffuse graybody. A heat transfer by radiation for straight dewars and its dependence on surface treatment of wall are discussed and compared with experimental results.
The Nb3Sn layer was formed at the interface between Nb and Sn-Cu alloy for a short reaction time near the temperature of 700°C. In case that the layer thickness of the Cu-Sn alloy on the surface of Nb is thicker than several μm, the Cu content of Cu-Sn alloy should be above 30 at.% to produce the Nb3Sn layer for a short reaction time at this temperature. When the layer thickness of Cu-Sn alloy plated initially is thinner than 1μm, even a Cu-Sn alloy with a less than 10 at.% Cu can produce the Nb3Sn by utilizing the variation of Cu concentration during reaction. The Nb3Sn layer having Tc of 18.05 with ΔTc of 0.05K was prepared from about 1μm thickness of 20 at.% Cu-Sn alloy reacted at the temperature of 720°C for 24h.
Aluminium stabilized superconducting cables were prepared in order to investigate their cryostatic stability. The sample are seven-strands cabled conducters composed of copper-clad, single core Nb-Ti wires and copper-sheathed, high purity aluminium wires and dipped in Pb-Sn solder. From the measurements of the voltage versus current characteristics, the cold end recovery current has been determined as a function of an external field. A considerable increase of the recovery current has been obtained as compared with the copper stabilized cable. Simple fabrication method proposed as well as the improved recovery current may prove the possibility of light-weight, compact superconducting magnets.
For low temperature vacuum seals, O-rings of soft metals such as indium, lead, and gold have been used extensively. Besides these, stainless steel hollow O-rings are also usable for the same purpose. No vacuum seal of this type, however, has been reported so far, which is proved to be leak-tight in liquid helium. We have found that commercially available silver-plated stainless steel hollow O-rings and Teflon-coated ones provide reliable superleak-tight seals and they can be used repeatedly.