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TY - CONF AU - Garg, P. AU - Bieler, T.R. AU - Cooley, L.D. AU - Solanki, K.N. ED - Michel, Peter ED - Arnold, André ED - Schaa, Volker RW TI - A First-Principles Study on Magnetic Flux Trapping at Niobium Grain Boundaries J2 - Proc. of SRF2019, Dresden, Germany, 30 June-05 July 2019 CY - Dresden, Germany T2 - International Conference on RF Superconductivity T3 - 19 LA - english AB - Niobium is basis for all superconducting radio frequency cavities, a technology that accelerates charged particle beams to energy levels not possible by other means. When cavities are pushed to limits, significant heating appears at extended material defects, like grain boundaries. Therefore, it is crucial to understand how grain boundary (GB) structure and associated properties lead to trapping of magnetic field, and whether GB itself has any unusual magnetic behavior. Using first-principles calculations, external magnetic field along the GB plane was simulated within an all-electron full-potential linearized augmented plane-wave framework. A ground state with non-zero flux, indicative of flux trapping, was obtained at some grain boundaries, this outcome being influenced strongly by GB local structure. Furthermore, electronic density of states and charge-transfer calculations suggested non-zero spin polarization at grain boundaries, which may be consistent with recent observations of unusual paramagnetic magnetization as a function of specimen surface area for cavity-grade niobium. PB - JACoW Publishing CP - Geneva, Switzerland SP - 565 EP - 569 KW - niobium KW - electron KW - cavity KW - simulation KW - radio-frequency DA - 2019/08 PY - 2019 SN - "" SN - 978-3-95450-211-0 DO - doi:10.18429/JACoW-SRF2019-TUP056 UR - http://jacow.org/srf2019/papers/tup056.pdf ER -