Abstract
Large-grain Nb has become a viable alternative to fine-grain Nb for the fabrication of superconducting radio-frequency cavities. In this contribution we report the results from a heat treatment study of a large-grain 1.5 GHz single-cell cavity made of “medium purity” Nb. The baseline surface preparation prior to heat treatment consisted of standard buffered chemical polishing. The heat treatment in the range was done in a newly designed vacuum induction furnace. values of the order of at 2.0 K and peak surface magnetic field () of 90 mT were achieved reproducibly. A value of at 2.0 K and was obtained after heat treatment at . This is the highest value ever reported at this temperature, frequency, and field. Samples heat treated with the cavity at were analyzed by secondary ion mass spectrometry, x-ray photoelectron spectroscopy, energy dispersive x ray, point-contact tunneling, and x-ray diffraction, and revealed a complex surface composition which includes titanium oxide, increased carbon, and nitrogen content but reduced hydrogen concentration compared to a non-heat-treated sample.
19 More- Received 23 October 2012
DOI:https://doi.org/10.1103/PhysRevSTAB.16.042001
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Published by the American Physical Society