Characterization of Nb Superconducting Radio Frequency Cavities Based On In-Situ STEM And EELS

Various impurities of Nb are investigated with atomic resolution. Methodologies for quantifying Nb oxides and hydrides are developed. Direct observation of hydrogen atoms is realized in ABF images at room temperature, and can also serve as a promising method to identify diff erent hydrides in Nb bulk at LN2 temperature if the cold stage is stable enough. My work on the local strain of Nb cavities points out that Nb carbides play a signi ficant role in the performance of SRF cavities at low temperature and intermediate to high fields.