Magnetic lenses are new devices that concentrate magnetic flux by using the diamagnetism of superconductors. Magnetic lenses of two types made from NbTi sheets were constructed; measurements were made on them and they were systematically studied. TypeA was constructed by stacking NbTi rings that had identical outer diameters and increasing inner diameters to form a hollow cone. Each ring had a slit to suppress the circumference current. Three construction methods for typeA were tested: the rings were stacked with their slits aligned but with no insulation between the rings (A-1), with their slits aligned and with insulation between the rings (A-2), and with their slits in different positions and with insulation between the rings (A-3). For typeB, sheets were rolled into hollow cones. Three identical cones were stacked to form a lens (B-1) and a single cone was used as a reference lens (B-2). The lenses were assembled in a cryocooler-cooled cryostat with a NbTi magnet. The quenching behavior, concentration ratio, hysteresis, and decay behavior were measured. Because of its larger dimensions, typeB had a larger concentration ratio (2.49 for B-1) than typeA (1.87 for A-1). Both lenses (typesA and B-1) were quenched when the concentrated flux density reached about 0.64T. The results suggest that quenching was caused by the NbTi sheet itself.
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