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

• Published in: Physical review special topics. PRST-AB. Accelerators and beams 2014-08, Vol.17 (8), p.083501, Article 083501
• Main Authors: Eozénou, F., Boudigou, Y., Carbonnier, P., Charrier, J-P., Gasser, Y., Maurice, L., Peauger, F., Roudier, D., Servouin, C., Muller, K.
• Format: Article
• Language: English
• Subjects: Baking; Electrolytes; Electrolytic cells; Holes; Low voltage; Niobium; Parameters; Sulfuric acid; Superconducting supercolliders; Superconductivity
• ISSN: 1098-4402; 1098-4402; 2469-9888
• DOI: 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−H2SO4 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 (25L/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 Q0 value at low and medium accelerating fields though limited by power losses due to field emitted electrons.