Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity

P. Dhakal; G. Ciovati; G. R. Myneni; K. E. Gray; N. Groll; P. Maheshwari; D. M. McRae; R. Pike; T. Proslier; F. Stevie; R. P. Walsh; Q. Yang; J. Zasadzinzki

doi:10.1103/physrevstab.16.042001

arXiv · 1210.6875

Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity

P. Dhakal·G. Ciovati·G. R. Myneni·K. E. Gray·N. Groll·P. Maheshwari·D. M. McRae·R. Pike·T. Proslier·F. Stevie·R. P. Walsh·Q. Yang·J. Zasadzinzki

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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 800 - 1400 C was done in a newly designed vacuum induction furnace. Q0 values of the order of 2x1010 at 2.0 K and peak surface magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0-value of (5+-1)1010 at 2.0 K and Bp = 90 mT was obtained after heat treatment at 1400 C. This is the highest value ever reported at this temperature, frequency and field. Samples heat treated with the cavity at 1400 C were analyzed by secondary ion mass spectrometry, secondary electron microscopy, 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.

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P. Dhakal, G. Ciovati, G. R. Myneni, K. E. Gray, N. Groll, P. Maheshwari, D. M. McRae, R. Pike, T. Proslier, F. Stevie, R. P. Walsh, Q. Yang, J. Zasadzinzki. 2012-10-25. Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity. https://doi.org/10.1103/physrevstab.16.042001

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