2016 年 51 巻 6 号 p. 248-258
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.