Influence of Anisotropy in Low Magnetic Field on 2G HTS Pancake Coils Under Liquid Nitrogen

This paper investigates how the current distribution and ac losses of second-generation high-temperature superconducting (2G HTS) pancake coils are affected by the material anisotropy. The 2G HTS tape has a strong anisotropy, which means that its critical current densities are different at different magnetic field orientations. 2G HTS pancake coils with different anisotropies have different ac losses. We studies this phenomenon by both experimental and numerical methods. Three 2G HTS coils with different turns are fabricated and tested in liquid nitrogen. AC losses with different frequencies are measured and compared with simulation. We use the critical-state model to calculate the current distribution and ac losses. Our modeling results are well validated by experimental measurements. We apply this numerical model to pancake coils with different anisotropies and calculate the current distribution, magnetic field, and ac loss. We find that the anisotropy of 2G HTS affects the ac loss and current distribution. It is possible to decrease the ac loss by an advanced pinning technique.