Speaker
Description
The performance of thin-film superconducting RF cavities is strongly dependent on the quality of the underlying copper substrate, whose surface morphology directly influences film growth, adhesion, and final RF behaviour. In the framework of thin-film R&D for future accelerators such as FCC-ee, achieving smooth, defect-free copper surfaces on full elliptical geometries is an essential prerequisite.
Plasma Electrolytic Polishing (PEP) offers an attractive alternative to conventional electropolishing, providing effective surface smoothing with environmentally friendlier electrolytes while avoiding aggressive acids. At INFN-LNL, PEP has been developed and applied to 1.3 GHz copper cavities for superconducting coatings — initially Nb, with the aim of transitioning to Nb₃Sn once the deposition process is mature.
In this contribution, we first present the principal challenges encountered in scaling PEP to a full elliptical cavity and the strategies adopted to make the treatment feasible. We then report on three cavities of different origin and fabrication history — bulk and hydroformed, with differing pre-treatments — all PEP-treated at INFN, Nb-coated at CERN, and RF-tested at CERN and KEK, reflecting a joint effort across the three laboratories. Finally, we outline challenges and mitigation strategies, including an electrolyte agitation approach.