Multilayer insulation (MLI) is essential for the thermal insulation of cryostat because the apparent thermal conductivity is much lower than that of other vacuum insulation such as evacuated fibrous insulation or powdered insulation. Thermal radiation through MLI is effectively suppressed by thin aluminized polyester (PET) films stacked around the cold surface. As gravity causes thermal contact between the adjacent PET films, the insulation performance of MLI is degraded considerably. To avoid this degradation, extremely thin PET films are chosen to achieve a lightweight MLI. It is important to fabricate MLI by placing the aluminized PET films one after another around the cold surface, so as to avoid extra contact pressure between the films. If the MLI is properly fabricated, it can be said it is in a state of self-compression. The most important factor among the test conditions of MLI thermal insulation performance is the interlayer contact pressure. If the experimental conditions of the interlayer contact pressure are not clarified, it is impossible to verify the data. The characteristics of materials for MLI are introduced in this report, and the measurement method and its accuracy for determining the interlayer contact pressure are described.
The strain effect of REBa2Cu3Oy (REBCO: RE = Y, Gd, Sm)-coated conductors (CCs) on critical current (Ic) is one of the most fundamental factors for superconducting coil applications. In this study, we aim to clarify the effect of artificial pinning center shapes on the strain effect in BHO-doped GdBCO CCs. To achieve this, we fabricated a Pure-GdBCO CC, a BHO nanorod-doped GdBCO CC and a multilayered-GdBCO (ML-GdBCO) CC, and carried out bending tests. As the result, the strain dependence of Ic for each CC showed an upward convex and the peak strain of the BHO-doped GdBCO CC shifts towards the compressive strain independent of the BHO shapes. In addition, the strain sensitivity of Ic in the GdBCO CCs including BHO becomes smaller. To clarify the difference between the strain sensitivity of Ic and the peak strain among the CCs, we evaluated the residual strain and the slopes of the internal lattice strains against the applied tensile strain (β). From this measurement, the residual strains for the Pure-GdBCO CC and the ML-GdBCO CC were almost the same. In addition, there was no change in the β value between the Pure-GdBCO and ML-GdBCO CCs. These results suggest that the changes in peak strain and strain sensitivity were not related to the internal lattice strain.