Glock, H.-W.; Knobloch, J.; Neumann, A.; Tamashevich, Y.; Kinzinger, J.; Böhnel, M.; Reims, N.: Operational Experiences with X-Ray Tomography for SRF Cavity Shape and Surface Control. In: Mark Boland ... [Ed.] : IPAC 2019, Proceedings of the 10th International Particle Accelerator Conference: Melbourne, Australia, 19-24 May 2019Geneve: JacoW, 2019. - ISBN 978-3-95450-208-0, p. WEPRB017/2838-2841
http://accelconf.web.cern.ch/AccelConf/ipac2019/papers/weprb017.pdf
Open Access Version
Abstract:
X-ray tomography has been established as a nondestructive three-dimensional analysis tool, commercially offered by industrial vendors. Typical applications cover shape control and failure detection (voids, cracks) deep inside of complicated bulk pieces like engine blocks, bearings, turbine blades etc.. We evaluated the applicability of the process for superconducting radio frequency cavities, in particular a generic 1.3 GHz single test cell cavity, the 1.4-cell 1.3 GHz bERLinPro electron gun cavity and the 1.5 GHz VSR-1-cell-prototype cavity. The gun cavity experienced severe shape modifications during its tuning process and features a complicated internal stiffening construction. Thus it is a challenge to measure its actual internal cavity surface shape after the complete preparation process with a resolution, sufficiently high (better than 0.2 mm) to serve as input for meaningful comparative field simulations. First tests with a vendor’s on-site X-ray source, operating at X-ray energies up to 590 keV revealed an insufficient resolution of the inner surface, attributed to the unfavorable X-ray damping characteristics of niobium. This was overcome with the aid of an accelerator-based source (X-ray spectrum up to 7.5 MeV), operated by Fraunhofer IISEZRT, Fürth, Germany. Results show significant, while understood, shape changes and indicate partial inner surface modifications of the gun cavity. Further, the data evaluation process, which was needed to provide input for field simulations, raised issues because of data set size and complexity and illustrated further some typical artefacts, which are discussed in the paper.