Nondestructive Inspection of Niobium to Improve Superconductivity

This paper demonstrates that the information needed to select the highest quality niobium is obtainable nondestructively . Performance improvements of particle accelerators using RF superconductivit y requires rapid nondestructive inspection of commercially pure niobium sheets in bulk for assurance of high purity, small grain size, freedom from critical defects and near 100% recrystallizatio n. A total of 1.5 square meters of 3.0 and 1.5 mm thick niobium sheet vas scanned uith a Scanning Laser Acoustic Microscope (SLAM) using acoustic resolution of up to 25-50 microns. We found -- acoustic attenuation in both niobium plates and velds depends on interstitial gas content; spatial variation in acoustic transmission depends on grain size; ultrasonic evidence of inadequate recrystallizatio n; i nternal delaminations; and that internal localized i nclusions and voids are detectable. A principle SLAM advantage is its combination o f high scan density and high scan rate (130 lines/mm a nd o ne square meter in 30 minutes at 60 MHz) making practical large quantity inspection (e.g. 100 tons proposed )