Title: Niobium Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: coating process and film characterization
Author: Alban Sublet
Abstract: The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a superconducting niobium thin film. The series production of the high-beta cavities has started. In parallel to the production, a systematic characterization of the film has been launched. Thickness measurement, RRR and FIB-SEM cross section and TEM analysis are conducted in collaboration with EPFL (CIME) to investigate the film growth and its morphological properties at different places along the cavity inner and outer conductor. Samples are produced in a test cavity with the baseline production coating recipe and in the same hardware to be as close as possible to the production conditions.
The production coating cycle and setup to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5×108) is described and the resulting niobium film characteristics is presented.