高能辐照对聚变磁体绝缘材料低温电绝缘特性的影响机理研究

The insulation materials of the superconducting magnet in magnet confinement fusion reactors were exposed in the severe environment such as cryogenic temperature (<7 K), high-energy irradiation and strong magnetic field. Insulation failure at cryogenic temperature is one of important factors contributing to magnet quenching. Therefore, it is necessary to investigate electrical properties of insulation materials from room temperature to liquid helium temperature before and after irradiation, in order to make sure safety operation of superconducting magnet in magnetic confinement fusion reactors. In the project, the electrical properties of glass fiber reinforced epoxy resin composites and polyimide films, such as electrical breakdown voltage, flashover properties, electrical resistance and dielectric properties will be systematic investigated from room temperature to liquid helium temperature before and after irradiation. In combination of the analysis of microstructure of the insulation materials, the mechanisms of cryogenic and radiation effect on electrical insulating properties will be discussed. The finish of the project will contribute to design and operation of the future superconducting magnet confinement fusion engineering reactor in China, and establish the basis for developing novel radiation-resistant insulation materials.

磁约束聚变装置中，超导磁体绝缘材料需要在低温(<7K)、高能辐照、强磁场的环境下工作。低温绝缘失效是引起超导磁体失超的重要原因之一。因此，为保证聚变堆中超导磁体的安全可靠运行，有必要深入研究高能辐照条件下绝缘材料在室温至液氦温区的电绝缘特性。本项目拟选择玻璃纤维增强环氧基复合材料以及聚酰亚胺薄膜作为研究对象，研究不同辐照剂量下绝缘材料在室温至液氦温区的电击穿强度、沿面闪络、电阻率以及介电性能等的变化规律，在此基础上结合微观结构的分析，探讨高能辐照和低温条件下电绝缘特性变化的机理，为未来我国独立建造超导磁约束聚变堆的可靠设计和运行提供参考，同时为开发新型耐辐照低温绝缘材料奠定理论基础。

针对国际热核聚变实验堆(ITER)及未来磁约束聚变装置中超导磁体对绝缘材料的要求，本项目以VPI工艺制备的环氧树脂基绝缘材料和聚酰亚胺薄膜为研究对象，开展高能辐照环境下聚变超导磁体绝缘材料的低温电绝缘特性研究,研究了高能辐照及温度对绝缘材料击穿强度、沿面闪络、介电性能和空间电荷的影响，研究结果表明，环氧树脂基绝缘材料的击穿强度和闪络电压随温度降低而升高。温度降至20 K过程中，介电损耗γ峰对应的频率变化不大，幅值随着温度降低呈整体下降趋势，且高频区域没有出现新的损耗峰，GFRP材料的环氧-玻璃纤维界面性能保持良好。200 K以下材料的电导率低，空间电荷限制电流阈值场强高，辐照对材料的作用表现为先交联后降解的过程，以降解过程为主，材料整体耐辐照性能较高。聚酰亚胺材料的相对介电常数随着辐照剂量的增大，表现为先增大后减小；经高能辐照后，聚酰亚胺试样表面陷阱捕获电荷的能力明显增强。