PHYSICAL AND CONSTRUCTIONAL PRINCIPLES FOR HIGH-T(C) SUPERCONDUCTING MAGNETS

The development of high temperature superconductors offers on the one hand a new possibility for building magnets due to their extremely hig h upper critical magnetic field, but represents on the other hand rigo rous limitations because of their relatively low critical current and rigid and brittle mechanical properties. Among the practicable methods of magnet manufacture the simplest one is to use ceramic spirals with conventional electrical contacts to convey the current. As a second p ossibility, solenoids of traditional type can be realized, based on cu t, electrically contacting rings. Both of these types can be supplied by conventional d.c. electrical treatment. These magnets can, however, create fields of only low intensity and the enormous power dissipatio n in the contact resistivities causes almost unsolvable cooling proble ms. In order to avoid these difficulties we have elaborated a new proc edure for building high-T(c) superconducting magnets, which seems to b e more useful from the point of view of applications. They are constru cted of individual rings and energized by a contactless external magne tic induction method. Subseqently, the persistent self current provide s a magnetic field for every ring. Stacking the rings on top of each o ther allows the magnetic field strength of the solenoid-like arrangeme nt to be increased, although the small critical current and the thickn ess of the rings limit its value. Further improvements may be looked f or using thick film- or thin layer systems, the high critical current densities of which guarantee a radical increase in the magnetic field. Among the superconducting materials, mainly the Y-Ba-Cu-O and Bi(Pb)- Sr-Ca-Cu-O compounds are worthy of consideration.