ACOUSTIC-EMISSION FROM NBTI SUPERCONDUCTORS DURING FLUX JUMP

In experiments with NbTi superconductors, the emission of acoustic waves in the frequency range 0.1 to 0.3 MHz was recorded during a current sweep. The acoustic emission as the current increased started at about 30% of the critical current and continued as the current decreased. The emission was reduced in subsequent current cycles which is explained by reduced magnetic flux motion due to the previously trapped flux. The reduction of acoustic emission in subsequent cycles proves definitely it is due to flux motion and excludes other possible sources like mechanical deformation. Results of different NbTi compositions are presented and discussed qualitatively. © 1979.