Recent results and encountered difficulties in the development of low loss fine filament composite superconductor are presented. The design criteria of superconductors for power frequency applications are discussed from the viewpoint of thermal properties, a.c. losses and the proximity effect and the critical elements to be satisfied by the a.c. conductors were clarified. The present state of the R & D of NbTi and continuous filament Nb3Sn composites is overviewed and special emphasis is placed on the identification of the problems of conductor fabrication and electromagnetic properties peculiar to ultrafine filament composites. The design parameters of ideal conductors are given in order to show the ultimate target.
This report reviews the current activity for the measurement of the superconducting critical current (IC) and a proposal for the standardization of the IC measurement and its attitude. The standard materials and the IC test standard method will be widely needed as primary standards in many diverse fields of science, industry, and technology, both within the nation and throughout the world. For many scientists and technologists at laboratories and companies it is of more than passing interest to know the measurements and methods. Although preliminary screening measurements of the several condidate conductors mainly for NbTi superconductor were started few years ago, these tests have to be established to generate data base for the standard test method of the IC measurement. The concensus in order to understand and to generate data base of the IC measurement has to be advanced as wide as possible, first. Second, a new measurement system is built to research needs, to define technical terms, to measure critical currents and to evaluate the test results. Third, an interim standard is approved by standards groups, such as an institute and a foundation, and volunteered to the national standards or the international standards. In practice, the interim or group standards in the third stage will become to be very important because of its quick response and its purpose orientation.