Köszegi, J.M. Knobloch, J. Kugeler, O. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-THPB018 English 766-770 THPB018 ion niobium cavity SRF background Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-THPB018 http://jacow.org/srf2017/papers/thpb018.pdf Over the past years trapped magnetic flux has emerged as a main limiting factor of high quality factors in SRF cavities. Several studies investigated how the ambient magnetic field can be minimized or how the flux expulsion during the phase transition can be improved. We now present a study that targets the pinning centers which allow for the flux to remain inside the superconductor in the first place. Using magneto-optical imaging we were able to not only measure the amount of trapped flux but in addition we managed to image its distribution with a resolution below 10μm and correlate it with electron backscatter diffraction maps. As a result we found that the grain boundaries did not play a major role as pinning centers nor did the crystal orientation influence the amount of trapped flux signifi-cantly. Niobium hydrides which formed during the cool down to cryogenic temperatures however were found to enhance trapping.