JLAB, Newport News, Virginia
NCSU AIF, Raleigh, North Carolina
The College of William and Mary, Williamsburg
Performance of SRF cavities depends on material within the shallow RF penetration depth. C, N, and O are of particular interest as interstitial contaminants and earlier work suggested very high H concentration*. Secondary Ion Mass Spectrometry (SIMS) has the sensitivity to quantitatively measure these species in the region of interest. However, standards for quantitative SIMS analysis of these elements in Nb did not exist. Initial attempts to develop an ion implanted standard were unsuccessful because of the roughness of the Nb surface. In this study, Nb samples were specially chemical mechanical polished and then subsequently treated with a light BCP. The result is a surface finish suitable for SIMS analysis and implantation standards. Ion implants of C, N, O, and deuterium (D) were obtained in Nb (and simultaneously in Si for dose verification). D was implanted to characterize H, and to avoid the high H background. The results show that D is apparently very mobile in Nb, and another approach will be required to quantify this element. This multi-element standard has already been of great benefit in characterization of C, O, and N in polycrystalline and large grain Nb**.
* A. D. Batchelor, et al. Proc. Single Crystal Niobium Technology Workshop, Brazil, AIP Conf. Proc., Melville, NY (2007) 72-83.
** P. Maheshwari, et al. Surface and Interface Analysis (in press)
BARC, Mumbai
JLAB, Newport News, Virginia
BARC-EBC, Mumbai
In recent years, large-grain/single-crystal niobium has become a viable alternative to the standard fine grain (ASTM grain size>6), high purity (RRR ) niobium for the fabrication of high-performance SRF cavities for particle accelerators In this contribution we present the results of a systematic study of the superconducting properties of samples obtained from four Niobium ingots (from CBMM, Brazil) of different purity. Measurements of bulk magnetization, surface pinning, critical temperature and thermal conductivity have been carried out on the samples subjected to different surface treatments such as buffered chemical polishing (BCP), 600C heat treatment, and low temperature baking (LTB). A correlation has been established between the LTB and the ratio of Hc3/Hc2. In addition, the phonon peak in the thermal conductivity data is suppressed by the presence of trapped magnetic vortices in the samples
