Thermal damage mechanism of xenon lamp silica envelope during high-power discharge

基于高功率激光装置对脉冲氙灯工程运行可靠性的要求,利用现有的能源模块开展了氙灯放电考核实验。实验结果表明:虽然氙灯运行在安全的能量负载水平,当能源模块单个放电回路的峰值功率超过300 MW时,氙灯石英玻璃管壁存在热损伤风险。肉眼观察到管壁损伤后在反射器对侧的灯管内壁出现乳白色沉积层。经扫描电镜和X射线光电子能谱测试分析,证实热损伤形成的乳白色沉积物为二氧化硅。为探究管壁热损伤机制,采用高速摄影观测了氙灯放电等离子体沟道发展过程。图像显示放大器内金属反射器的几何形状对放电沟道的分布产生了显著影响,尤其是在侧灯箱,灯内电弧沟道会靠近反射器一侧集中分布,因此,导致等离子体对灯管的偏烧。当放电峰值功率超过石英热负载极限时,管壁表面二氧化硅材料会被烧蚀至蒸发、气化,并随后沉积在灯管较冷部位。研究结果表明放电回路的放电峰值功率过高、放大器内金属反射器均会对氙灯造成热损伤。To improve the reliability of xenon lamps in optical amplifier of inertial confinement fusion (ICF) facility, high power xenon lamps were tested with the power modules similar to NIF facility in US. Though operating at a relatively safe energy loading factor of 0.2 or so, unexpected behavior of some lamps was observed while peak power value of discharge pulse was higher than 300 mega watts. Milky white participants appeared in the inner surface of the quartz envelope opposite to metallic reflector inside amplifier. Scanning electron microscopy and X-ray photoelectron spectroscopy data demonstrated that the chemical composition of whitish participant was SiO_2. To understand the thermal damage mechanism of the lamp envelope, the plasma channel profiles were captured by a high speed CCD camera. The photographs indicated that the existence of metallic reflector beside silica envelope resulted in an uneven distribution of plasma. The temperature was higher in the region with high plasma density. This leaded to local evaporation of silica glass and the whitening of quartz envelope. The results are helpful to optimize the design of discharge circuit of power module and reflector of amplifier of ICF facility