Physical and constructional principles for high-Tc superconducting magnets

Abstract

Abstract The development of high temperature superconductors offers on the one hand a new possibility for building magnets due to their extremely high upper critical magnetic field, but represents on the other hand rigorous 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 possibility, solenoids of traditional type can be realized, based on cut, 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 dissipation in the contact resistivities causes almost unsolvable cooling problems. In order to avoid these difficulties we have elaborated a new procedure for building high-Tc superconducting magnets, which seems to be more useful from the point of view of applications. They are constructed of individual rings and energized by a contactless external magnetic induction method. Subseqently, the persistent self current provides a magnetic field for every ring. Stacking the rings on top of each other allows the magnetic field strength of the solenoid-like arrangement to be increased, although the small critical current and the thickness of the rings limit its value. Further improvements may be looked for 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.