May-Mann, J. Eichhorn, R.G. JACoW Geneva, Switzerland 978-3-95450-178-6 10.18429/JACoW-SRF2015-MOPB013 English 105-109 MOPB013 cavity simulation factory superconducting-cavity focusing Contribution to a conference proceedings 2015 2015-12 http://dx.doi.org/10.18429/JACoW-SRF2015-MOPB013 http://srf2015.vrws.de/papers/mopb013.pdf Trapping or expulsion of ambient magnetic field has become an important factor in the performance of superconducting cavities with very high Q. As experimental data is limited, we set up a numerical field calculation model to study this effect in more details. We will report, how the cavity orientation, the movement of the transition to superconductivity front, and the orientation of the magnetic field contributes to the amount of magnetic field being vulnerable for trapping.