Hybrid composite pipes reinforced with high-strength polyethylene fiber (DF) and glass fiber (GF) were prepared to develop the coil bobbin for stable superconducting coils. The bobbin that in which the circumferential thermal strain expands with cooling and in which the circumferential Young's modulus is large would be effective for stable coils. The unidirectional DGFRP showed negative thermal expansion coefficient, and its Young's modulus was similar to DFRP in fiber direction; Young's modulus perpendicular to fiber direction was larger than that of DFRP. The circumferential Young's modulus of DGFRP pipe did not decrease with the filament winding (FW) angle to compare with DFRP. The calculated thermal strain with a cooling of the pipe showed good agreement with the average of observed inner and outer thermal strains. The circumferential thermal strain showed an expansion with FW angle of 50-90 deg and the absolute value was smaller than that of DFRP. The inner and outer circumferential thermal strains were different. The difference decreased with increasing inner diameter/thickness, and the differences were smaller than those of DFRP. The experimental data were obtained to make it possible to devise a coil bobbin with negative thermal expansion coefficient by DGFRP.
Alumina ceramics (Al2O3) is well known as an excellent material for insulation equipment, such as insulation breaks and feed-through terminals, at room temperature. A mechanical test of the ceramics was carried out for the application of an insulation break at low temperature. The insul