SQUID-based Nondestructive Testing Equipment of Dished Niobium Sheets for SRF Cavities

79784S05 In superconducting cavities used in nuclear physics research, the detection of impurities on to less than 50 micrometer sizes would enable the cavities to reach the highest possible accelerating fields. Currently available equipment can only inspect flat sheets, which allows for defective sheets to be eliminated before the expensive forming and machining of the cavity half-cells. However, this technology does not eliminate the problem of impurities that may remain after partial chemical etching of the half-cells, nor does it detect any defects that may have been added during the fabrication of the half-cells. This project will develop nondestructive equipment that can scan dished niobium sheets for superconducting radio frequency (SRF) cavities, allowing inspection and detection during the entire cavity manufacturing process. The technology will be based on an existing, sensitive SQUID (Superconducting Quantum Interference Device) system with gradiometer probe, non-magnetic dewar, data acquisition system, and a three dimension tracing mechanical system. In Phase I, the detection sensitivity of the SQUID pickup coils will be increased by modifying the existing flat-sample scanning table to allow the system to scan curved surfaces. A two- dimensional inducer will be developed to generate eddy currents in orthogonal directions. Finally, test scans will be performed to verify the functioning of the system. Commercial Applications and Other Benefits as described by the awardee: The instrument ultimately should allow the achievement of the highest possible accelerating field in cavities. In turn, the increased accelerating field would provide a considerable cost reduction for new accelerators as well as for upgrades of existing accelerators.