Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
ANL, Argonne, Illinois, USA
Recent progress on vapour diffusion coated Nb3Sn SRF cavities makes this material a very promising alternative for CW medium field SRF applications. In this paper we report on several systematic studies to determine the sources currently limiting the performance of Nb3Sn cavities to determine improved coating parameters to overcome these limitations. These include a detailed study of the sensitivity of Nb3Sn to trapped ambient magnetic flux, a first measurement of the field dependence of the energy gap in Nb3Sn and detailed measurements of the stoichiometry of the obtained Nb3Sn coatings with synchrotron x-ray diffraction and STEM. Initial results from a study on the impact of the coating process parameters on energy gap, Q-slope, and residual resistance, show clear dependencies, and thus directions for process optimization.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
ANL, Argonne, Illinois, USA
Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing.