Recently, high Tc superconducting Y-Ba-Cu-O with relatively high critical current density Jc can be produced by means of various types of melt processes. Applications of the superconductors to bulk magnets, high field shielding, magnetic levitation and so on, are proposed, since the high Jc of the superconducting bulk results in capturing of dense magnetic flux and repelling of high magnetic field. In the present review, it is first pointed out that feasible bulk current density in the superconductors are restricted not only by weak couplings between sub-structures but also by electro-magnetic properties such as flux creep and flux jump. The processing of bulk Y-Ba-Cu-O is outlined at viewpoint of improvement of Jc, while the limited level of the current density due to the undesirable phenomena is presented. Experimental and theoretical works for the prospective applications of high Tc bulk superconductors are summarized.
A small liquefier/refrigerator is a powerful equipment for people using liquid helium in their experiments. In this paper, the fundamental thermodynamics and some crues are reviewed for the one having a plan to install the equipment. The required High Pressure Gas Reuration is briefly mentioned.
In order to increase the luminosity of the TRISTAN electron-positron collider, eight superconducting quadrupole magnets are required. For this purpose, KEK has developed an iron-free quadrupole with a field gradient of 70T/m. It has an inner diameter of 140mm and an effective length of 1.145m. The coils, which are of cos 2Θ type, are made from four layers of 27-strand NbTi Rutherford-type cable with Kapton insulation and firmly clamped with 316LN stainless steel collars. Following the successful test of a prototype, nine quadrupoles were manufactured by industry, for which KEK provided all scientific and tehnical information about the magnet, and were installed in the TRISTAN main ring. Since they were commissioned in January 1991, the eight quadrupoles have been operated without trouble and the luminosity has been improved up to about twice the old value. The total operating time of the magnets is presently about 10, 000 hours. In this paper, a brief description of the magnets and the results of the tests as well as the experience over the first two years of operation are presented.