Improvement of the polishing treatment for niobium surfaces of superconducting cavity resonators
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For superconducting cavities made from niobium sheet, which are interesting in the field of accelerator applications, smooth and defect free inner surfaces are needed to achieve a high unloadedQ along with high accelerating field strength. These can be obtained using chemical polishing procedures. Whereas normally a mixture of HF, HNO3, and H3PO4 is applied, we chose the known bath containing HF, HNO3, and H2SO4 and worked above 50 °C. The surface quality was judged by visual inspection using a light microscope as well as by microwave measurements of one spherical resonator. The new method gave less grain boundary etching and, with high field levels, an enlarged unloadedQ.
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