This paper reviews supercritical helium gas cooling methods. The thermal transport properties of supercritical helium near 4.2°K are collected. Cryogenic helium pump or bellow pump for forced supercritical circulation is adequate to the laboratory-scale cooling system. The superconducting composite configurations with hollow conductors are used for supercritical channel forced cooling.
Hydrogen was first liquefied in 1898. However, more than a half-century, liquid hydrogen was liquefied in small quantities in a few cryogenic laboratories in the world. But now the industrial importance of liquid hydrogen is well recognized. In U.S.A. and Europe, it is produced and utilized in large quantities in chemical and nuclear propulsion, production of heavy water, bubble chamber in nuclear study and some other fields of science and industry. In our country, liquid hydrogen industry is still in its infancy, but quite recently 75cm liquid hydrogen bubble chamber and its refrigeration system having the capacity of 1kW at 20°K region have installed in the University of Tokyo. In this paper, the trends of liquid hydrogen industry in the world are reviewed and also comments are described in some possible utilizations of liquid hydrogen.
Recent developments on the study of flux flow in non-ideal type-II superconductors are reviewed mainly from the theoretical point of view. In non-ideal samples, fluxoid-pin interactions appear, together with the interactions between flux-line lattice defects and crystal lattice defects. These interactions affect the motion of flux-line lattice, and hence the mechanism of flux flow in non-ideal samples is different essentially from the flow in ideal samples. For engineering applications of superconducting phenomena, non-ideal type-II superconductors are widely used as materials. The materials are used under various conditions and circumstances, and a detailed information on flux-flow provides one of the important bases on the engineering design and analysis. It is, however, very hard to construct a long pipe connecting between a microscopic standpoint and an engineering design. Such a pipe has not yet been constructed in spite of energetic efforts of many workers.