Magnetic field, temperature and mechanical crack performance of a GdBCO magnetic lens

Magnetic field concentration by using the diamagnetism of a superconductor is a novel technique that has been experimentally demonstrated in magnetic lenses. A magnetic lens consists of a hollow superconductor cylinder with a tapered inner diameter within which the magnetic flux is concentrated by diamagnetism. Magnetic lenses are very promising for use in compact high magnetic field systems. However, magnetic lenses with large inner diameters are required to facilitate sample access during use. In this study, an optimized GdBaCuO magnetic lens with large inner and outer diameters was designed and its performance was investigated in liquid nitrogen, liquid helium, and a cryocooler-cooled cryostat. A lens with an inner diameter of 12mm was constructed by stacking three specially machined GdBaCuO bulk pieces. This magnetic lens cracked due to the large flux jump that occurred when the concentrated field of the magnetic lens exceeded 10T at 4.2K. The cracked lens was subsequently impregnated with epoxy resin. A concentrated field of 12.42T was realized when the background field was 8T at 20K and no flux jumps occurred. This result demonstrates that this GdBCO magnetic lens is promising for use in compact superconducting magnet systems.