Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

• Main Authors: F. Eozénou, Y. Boudigou, P. Carbonnier, J-P. Charrier, Y. Gasser, L. Maurice, F. Peauger, D. Roudier, C. Servouin, K. Muller
• Format: Article
• Language: English
• Published: American Physical Society 2014-08-01
• Series: Physical Review Special Topics. Accelerators and Beams
• Online Access: http://doi.org/10.1103/PhysRevSTAB.17.083501

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.