托卡马克第一镜反射率的衰变直接关系到各种光学诊断信号的有效性，决定了第一镜的使用寿命与各种常规光学诊断系统能否应用在大型超导托卡马克装置中。适当防护可维持第一镜反射率，而清洗可主动恢复部分第一镜反射率，防护与清洗是提高第一镜使用寿命的有效方法。本申请拟在EAST托卡马克装置及相关材料实验平台上开展挡板防护、加热与充气对第一镜表面沉积的抑制实验，并运用蒙特卡罗程序ERO对实验结果进行模拟，阐明不同方法维持第一镜光学反射率的机理与效率；另一方面，开展等离子体及激光清洗第一镜表面沉积的实验研究，对不同清洗方法主动恢复第一镜反射率的参数进行优化，并对比清洗效率，提出延长第一镜使用寿命的有效方法，并将其应用于EAST上主要的光学诊断系统。本项研究不仅可为国家大科学工程项目EAST提供延长第一镜使用寿命的有效方法，而且可为ITER及未来聚变装置光学诊断第一镜的研究提供科学基础并积累经验。

The degradation of first mirrors (FMs) reflectivity in tokamak, which is directly related to the effectiveness of various kinds of optical diagnostic signals, determines the lifetime of the FMs and the application of various conventional diagnostic systems in a large-size superconducting tokamak. The reflectivity of the FMs could be maintained by proper protections and recovered partly by active cleaning, and therefore, both of protection and cleaning are effective methods to prolong the FMs lifetime. This application proposes to carry out the deposition mitigation experiments for FMs by means of ducts protection, heating and gas puffing at EAST tokamak and its materials and plasma evaluation system (MAPES).With simulations of experimental results by the Monte Caro code ERO,the mechanism and efficiency of the FMs reflectivity maintenance by different methods will be clarified. On the other hand, experimental studies on plasma and laser cleaning of the FMs surface deposition will be performed. The parameters will be optimized and cleaning efficiencies will be compared for different methods on actively recovering the FMs reflectivity. Then, an effective method to prolong the FMs lifetime will be proposed, and applied to the various kinds of optical diagnostic systems in EAST. This study will not only provide the effective method to prolong the lifetime of FMs for national giant scientific project EAST, but also provide significant scientific basis and accumulated experiences for studying the optical diagnostic first mirrors in ITER and the future fusion devices.