High Resolution and Fast Scanning Speed SQUID Based Nondestructive Inspection System of Niobium Sheets for SRF Cavities

Applications in high energy physics and other fields require the use of thousands of superconducting radio frequency (SRF) cavities made of high purity niobium (Nb) material. However, tantalum, the most prolific of metal inclusions, can cause thermal breakdown in these cavities. This project will develop a nondestructive system based on superconducting quantum interference devices (SQUID), which will scan Nb sheets used in the manufacturing of SRF cavities. The system will provide both high speed and high resolution, detecting tantalum defects as small as 25 microns. Phase I will modify an existing SQUID-based eddy current system to detect Ta defects smaller than 50 microns and also identify techniques to achieve the fast scanning of a large number of Nb sheets in a reasonable time and with higher resolution. In Phase II, the system will be further optimized, sensitivity will be improved, and the software will be enhanced. Ultimately, the system will be capable of scanning a 30cm x 30cm Nb sheet and detecting Ta defects smaller than 25 microns in less than 10 minutes. Commercial Applications and other Benefits as described by the awardee: The inspection system should enable the achievement of the highest possible accelerating field in SRF cavities. This cost reduction would be realized either by reducing the length of SRF cavities or by allowing the installation of higher gradient cavities for energy upgrades occupying the same space. The system also should find use in the detection of defects on the surface, inside the bulk, or at the back side of metallic sheets and structures used in other industries.