Mechanical Losses Due to Frictional Heat in Bi-2223 Tapes With Structural Materials of Various Thermal Expansion Properties

We have experimentally studied relation between mechanical losses and thermal expansion properties in superconducting coils. For the experiments, three kinds of structural materials (GFRP, DGFRP, and ZFRP) were used. A glass fiber reinforced plastic (GFRP) contracts with decreasing temperature; on the contrary, a Dyneema and grass fiber reinforced plastic (DGFRP) and a Zylon fiber reinforced plastic (ZFRP) expand with the decrease of temperature. We used sample holders made of those plastics and measured AC current losses of a Bi-2223 tape in liquid nitrogen. Even if the magnetic field applied to the tape and an AC transport current of the tape were same, the loss depended on the sample holder materials. When the sample holder is the GFRP, the loss was largest in the three kinds of plastics, and in case of the ZFRP, the loss was smallest. The ZFRP has the largest expansion property of the three materials, that is, the loss decreased with expansion of the sample holder´s materials