Wuppertal 2015 – scientific programme
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AKBP: Arbeitskreis Beschleunigerphysik
AKBP 6: SC Resonators
AKBP 6.5: Talk
Tuesday, March 10, 2015, 14:45–15:00, BZ.08.06 (HS 1)
Surface study of centrifugal barrel polished 1.3 GHz Nb cavities — •Yegor Tamashevich1,2, Eckhard Elsen2, Brian Foster1,2, Aliaksandr Navitski2, and Alena Prudnikava1,2 — 1DESY, 22607 Hamburg, Germany — 2University of Hamburg, 20146 Hamburg, Germany
Superconducting radio-frequency (SRF) cavities are the key components of accelerators such as the European X-ray Free Electron Laser and the planned International Linear Collider (ILC). Centrifugal barrel polishing (CBP) is a promising technique both for repairing and improving the performance of such cavities due to ability to remove large defects effectively and obtaining mirror-like surface without chemistry. In spite of numerous attempts, the CBP-treated cavities show yet worse SRF performance than expected. The present study explores the multi-step recipe last developed at FNAL/JLab by using a coupon cavity with removable samples. It allows investigation of the interior surface after each polishing step by microscopic techniques such as laser profilometry, SEM/EDX, AFM etc. and measurement of the roughness and material removal rates at the most relevant areas. The study reveals some polishing media (e.g. Al2O3) to be embedded into the surface which causes new surface scratches in the final polishing step and * being normal conducting * most probably the worsening of the SRF performance. Additionally, a possibly detrimental shearing and deformation of the upper surface layer is observed. An improvement of the recipe is under study.