Study of second generation, high-temperature superconducting coils: Determination of critical current

Reference:

Zhang, M., Kim, J.-h., Pamidi, S., Chudy, M., Yuan, W. and Coombs, T. A., 2012. Study of second generation, high-temperature superconducting coils: Determination of critical current. Journal of Applied Physics, 111 (8), 083902.

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Official URL:

http://dx.doi.org/10.1063/1.3698317

Abstract

This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns’ electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper.

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