Kramer, F.; Keckert, S.; Kugeler, O.; Knobloch, J.; Kubo, T.: Modelling Trapped Flux in Niobium. In: Kenji Saito ... [Ed.] : SRF2023 : Proceedings of the 21st International Conference on RF Superconductivity, Grand Rapids, MichiganGeneve: JACoW, 2023. - ISBN 978-3-95450-234-9, p. TUPTB002/1-5
https://srf2023.vrws.de/papers/tuptb002.pdf
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Abstract:
Detailed measurements of magnetic flux dynamics and trapped magnetic flux in niobium samples were conducted with a new experimental setup that permits precise control of the cooldown parameters. With this setup the dependency of trapped flux on the temperature gradient, external magnetic field, and cooldown rate can be mapped out in more detail compared to cavity measurements. We have obtained unexpected results, and an existing model describing trapped flux in dependence of temperature gradient does not agree with the measured data. Therefore, a new model is developed which describes the magnitude of trapped flux in dependence of the temperature gradient across the sample during cooldown. The model describes the amount of trapped flux lines with help of a density distribution function of the pinning forces of pinning centers and the thermal force which can de-pin flux lines from pinning centers. The model shows good agreement with the measured data and correctly predicts trapped flux at different external flux densities.