Increase of Thermal Stability Caused by High Thermal Conduction Fiber and Sheet in Conduction-Cooled HTS Coils

We have examined thermal stability in high-temperature superconducting (HTS) coils, focusing on thermal properties of coil's structural components. As the component materials, high thermal conduction fibers and sheets made from a liquid crystal polymer (LCP) were used. First, we fabricated an LCP fiber reinforced plastic (LCP-FRP), and experimentally estimated thermal conductivity of the LCP-FRP round rod at cryogenic temperature, and made sure the conductivity was high. Next, thermal strain of the LCP-FRP rod from room temperature to 77 K was measured. From the results, the LCP-FRP bar expanded to a longitudinal direction of the bar with the cool down. Finally, we made an experimental apparatus which simulated a part of the HTS coil, and inserted the LCP sheet or a GFRP sheet in the HTS coil model. When the model was heated by a local heater, temperature rise of the model having the LCP sheet was lower than that having the GFRP sheet. From those experimental results, we think that thermal stability of the HTS coil becomes better by using the LCP sheet for non-metallic structural component in the coil.