An advanced setup for vertical electropolishing of superconducting radio-frequency niobium elliptical cavities has been installed at CEA Saclay. Cavities are vertically electropolished with circulating standard HF-HF-H 2 SO 4 electrolytes. Parameters such as voltage, cathode shape, acid flow, and temperature have been investigated. A low voltage (between 6 and 10 V depending on the cavity geometry), a high acid flow (25 L= min), and a low acid temperature (20°C) are considered as promising parameters. Such a recipe has been tested on single-cell and nine-cell International Linear Collider (ILC) as well as 704 MHz five-cell Super Proton Linac (SPL) cavities. Single-cell cavities showed similar performances at 1.6 K being either vertically or horizontally electropolished. The applied baking process provides similar benefit. An asymmetric removal is observed with faster removal in the upper half-cells. Multicell cavities (nine-cell ILC and five-cell SPL cavities) exhibit a standard Q 0 value at low and medium accelerating fields though limited by power losses due to field emitted electrons.
The Saclay program of R&D on RF superconductivity is continuing, with applications in the frame of the TESLA and ELFE projects. The main topics under study have been the research of high accelerating gradients, and low RF dissipation in superconducting cavities. Thin superconducting films have also been investigated. We report substantial progress in these three areas.
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