General aspects of β-W type compounds with high superconducting critical temperatures are given. Critical temperatures of superconducting compounds are mainly affected by factors of crystal structure, lattice constant, and stoichiometric composition. It is emphasized that the critical temperature of the β-W type compound is increased with the lattice constant approaching to an ideal stoichiometric value. The extrapolated plots of critical temperature and lattice constant suggest that the critical temperatures of stoichiometric compounds Nb3Ge and Nb3Si can be enhanced up to near 26K and 30K, respectively. Magnetic field dependence of a critical current density was also discussed about a coevaporated Nb3Ge thin film.
The stability of superconducting hollow conductor has been widely discussed, but almost all of them are concerned with the case of a superconducting magnet. In this paper, the stability condition against pulsive heat inleak is ascertained by numerical computation for a realistic power transmission line model.
This report describes the development and the reliability study of the Kirk cycle miniature refrigerator manufactured for trial. Firstly, we show the reason why the Kirk cycle is adopted for the refrigeration, and deal with the structure of cryogenic miniature refrigerator. The refrigeration power of this refrigerator is 72 watts max, at an operating temperature of 77K, and excellent characteristics are obtained in the actual COP, the specific volume and the specific weight. Secondly, we pointed out the failures of the trial Kirk cycle refrigerator. General failures may be divided into four modes; catastrophic, critical, marginal and negligible failures. We investigate the critical failures of the swash plate type driving system, and the calculated results of the reliability are given.