Study on the Performance of Glass Fiber Used for Superconducting Magnet Insulation Before and after Vacuum Heat Treatment Process

A long time 640℃ vacuum heat treatment is needed for the Nb₃Sn superconducting magnet to form the superconducting phase. Vacuum pressure impregnation(VPI)was carried out for the Chinese E glass fiber,HS/6 high-strength glass fiber and American S-2 high-strength glass fiber used in different superconducting magnet insulation structures before and after the vacuum heat treatment process at 640℃. We discuss whether the Chinese glass fiber can reach the performance of American S-2 high-strength glass fiber after the vacuum heat treatment process at 640℃ and meet the requirements of Nb₃Sn superconducting magnets. The effect of glass fiber on the mechanical and insulation properties of glass fiber reinforced resin matrix composite(GFRPs)after the vacuum heat treatment process was investigated. The tensile strength,interlayer shear strength,and DC withstand voltage breakdown tests were carried out at RT before and after vacuum heat treatment. After the vacuum heat treatment process,the tensile strength and interlayer shear strength of these GFRPs have been greatly degraded. The HS/6 high-strength glass fiber exhibits the best mechanical properties before and after the vacuum heat treatment process,also has the highest retention rate,and meets the requirements of use. The DC withstand voltage breakdown experiment shows that the electrical strength of HS/6 high-strength GFRP after vacuum heat treatment process is40% lower than that of S-2 high-strength GFRP,which cannot satisfy the requirements for usage,and the E GFRP loses its insulation properties.