Validation of Finite-Element Models of Persistent-Current Effects in Nb3Sn Accelerator Magnets

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Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated using three state-of-the-art Nb3Sn accelerator magnets featuring different subelement diameters, conductor critical currents, magnet designs and test temperatures. The temperature dependence of the persistent current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent-current effects is discussed. The strengths, limitations and possible improvements of the approach are also discussed.



Nb3Sn, accelerator magnets, field quality, mangetization


Published version: IEEE Transactions on Applied Superconductivity (Volume: 25, Issue: 3, June 2015) Article Sequence Number: 4003006.