| 题名 | 大功率脉冲氙灯失效机理分析及性能优化研究 |
| 作者 | 刘建军 |
| 学位类别 | 博士 |
| 答辩日期 | 2014 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 胡丽丽 |
| 关键词 | 惯性约束聚变 脉冲氙灯 失效 等离子体 |
| 其他题名 | Study on failure mechanism of high power xenon flashlamp and optimization of pump performance |
| 中文摘要 | 激光惯性约束核聚变（ICF）是当今国际上的重大基础科研课题，也是国内外研究的前沿和热点领域。大功率脉冲氙灯作为ICF激光器驱动器的泵浦光源，它需要承载全部输入电能后将其转换为辐射能，以实现对钕玻璃激光工作物质的高密度泵浦，其运行的可靠性和稳定性直接决定装置的运行状态。因此，研究大功率脉冲氙灯失效机理和破坏机制并有效降低失效几率是一个重大的研究课题，它对我国ICF激光驱动装置的建设具有重要意义。 随着ICF驱动器的规模越来越大，对泵浦光源的要求也不断提高。一方面要求泵浦氙灯的功率负载更强，能量增益水平更高；另一方面，为增加脉冲氙灯的堆积密度以提高单位空间输入的能量和泵浦效率，脉冲氙灯的尺寸也越来越大。因此，脉冲氙灯在放大器中的数量和规格都不断提高，如美国NIF装置要使用7680支Ф48×1800mm规格的大功率脉冲氙灯，所以其可靠性水平也愈发重要。 大功率脉冲氙灯在ICF装置运行中出现的故障被归纳为氙灯爆炸、电绝缘击穿和触发失效三类，除此之外，还存在两类导致氙灯光输出衰减的“软”失效：电极溅射和灯管因过度光照出现退化。两类“软”失效在氙灯长期运行后变得甚为突出，已引起人们的重视。为了满足ICF激光装置的运行稳定性要求，国际上对脉冲氙灯提出了接近“三零”技术指标，即“零击穿、零爆炸、零失效”。通过材料研发和结构工艺改进，我们研制的大功率脉冲氙灯已经基本实现了“零击穿”和“零爆炸”，但与工程装置的需求仍然存在较大的差距。本文重点研究了大功率脉冲氙灯在ICF装置条件运行时的破坏和失效机制，并基于驱动器对能量增益的要求开展了脉冲氙灯性能优化技术的探索，实验和研究结果可为降低大功率脉冲氙灯失效率、改善氙灯在装置中的工作性能提供参考。 本论文共包含六章：前两章分别为文献综述和实验方法及理论基础，第三、四、五章为论文的核心内容，第六章为结论。 文献综述部分介绍了脉冲氙灯工作特性和失效机理研究进展，综述了脉冲氙灯用于ICF装置的可靠性现状，并提出了本文的研究思路和内容。 第二章介绍了大功率脉冲氙灯电弧沟道高速摄影、辐射光谱分布测量、能量辐射效率测量和可靠性考核实验方法，以及脉冲氙灯V-I特性、电光转换效率的Trenholme模型、极限负载能量和寿命理论。 第三章研究了大功率脉冲氙灯放电沟道的演化过程、形态特征和影响因素。利用高速摄影等技术对大功率脉冲氙灯放电等离子体通道的发展规律、分布形态及影响因素进行了比较全面的实验测试，重点针对外部电场对电弧沟道的影响和作用机制进行了研究分析。结果表明氙灯放电沟道的发生和发展过程具有随机性，外部电场会显著影响甚至决定电弧沟道的分布形态，电弧沟道独特的分叉和裂化现象，以及多灯串联放电时个别氙灯电弧沟道形态的随机性，本质上都是由外在电场强度分布状况决定的。此外，提高充电电压可以改善主放电等离子体通道的均匀性与充盈度，有助于提高等离子体通道的亮度，但等离子体通道的剧烈扩张过程会增加对灯管的冲击。主、预脉冲时间间隔会对主脉冲初始时刻等离子体通道的形态产生影响，会影响主放电等离子体通道达到最高亮度时的充盈度，为了利用预电离的这一特点，需要优化选取主、预脉冲时间间隔。 第四章研究了石英玻璃管壁热损伤机制和灯管在长期光照作用下的特性变化，以及放电过程中钨电极表面区域的现象和特性。模拟真实腔内放电和运行条件对大功率脉冲氙灯进行了放电可靠性考核实验，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300MW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XPS能谱分析，证实热损伤形成的乳白色沉积物为SiO2。放电等离子体沟道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，因此导致了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，管壁表面材料会被烧蚀至蒸发、气化，并随后沉积在灯管较冷部位，形成SiO2沉积层。这种管壁发白现象会影响氙灯的辐射效率，抬高氙灯着火电压，进而导致氙灯触发失效。在氙灯长期放电过程中的紫外波段光照和高温等离子体热作用下，石英玻璃灯管中的元素Ce离子会由Ce3+转变成Ce4+，从而导致荧光强度的衰减。对大功率脉冲氙灯电极的测试分析结果表明，掺杂稀土Ce元素的钨电极材料在经过热处理激活后会在表面形成Ce原子的富集区，这有利于提高电极的电子发射性能。通过高速摄影观察和SEM微区形貌分析显示脉冲氙灯放电过程中阴极表面存在大量阴极斑点，斑点区域发生的熔蚀和微爆炸导致了阴极溅射现象的发生。而阴极溅射在脉冲氙灯长期放电后的累积效应会大幅降低石英玻璃灯管的透过率，从而导致光输出的减少。 第五章研究了预电离和电流截波技术对大功率脉冲氙灯性能的优化作用。实验研究了预电离技术对大功率脉冲氙灯放电回路及辐射特性的影响，发现存在一个最佳的主、预延时t（本文实验条件下为250~300 μs）使脉冲氙灯辐射效率最高，相比无预电离情况可提高3.8% ~5.1%；而当延时t值小于预电离脉冲持续时期时，预电离回路会受到主放电回路影响而出现振荡，且氙灯辐射效率反而会下降10%以上。此外，开展实验探索和研究了脉冲氙灯主放电流尾部截断技术对氙灯工作特性的影响。结果表明在氙灯主放电后300μs截断电流减少馈入氙灯的能量约占总能量26%。因此，主放电流波形截尾能有效降低管壁负载，提高氙灯寿命。 第六章是本论文的结论部分，总结了文中的实验结果并指出研究中存在的不足之处和对今后工作的展望。 |
| 英文摘要 | Inertial confinement fusion (ICF) is an important basic research issues in the world and many countries have done a lot of work on it. High power xenon flashlamp is mainly used in ICF research as the optical pump source, and its function is converting the input electric energy into radiation that can be absorbed by Nd: glass to achieve high pumping indensity. Since the reliability and stability is an important deciding factor of the ICF research. Also the high power xenon flashlamp is a key device in amplifier and is also one of the crucial technologies in Shenguang equipment in our country. So the study on failure mechanism and decreasing the failure probability is significant for construction and operation of ICF driver. With the larger scale and size of ICF amplifier, the requirements for pump source are increasingly improved. On the one hand, the xenon flashlamp need to operate at condition of high energy and power load to obtain higher gain level. On the other hand, to get input energy and pumping efficiency the stack density of elements is increased. Thus the number and size of xenon flashlamps used in amplifier are also increased constantly. For example, the National Igition Facility (NIF), consists of 192 laser beams and 7680 falshlamps which has arc length of 180 cm and bore diameter of 48 mm. Flshlamp failures of the following three different types have occurred during the operation of ICF amplifer: explosions, electrical insulation failures in the bases and leads, and trigger failures. In addition, there are other two types of “soft” failure mode—electrode sputtering and quartz solarization—that diminish the optical output of flashlamp as the number of shots increases. To meet the requirements of reliability and stability of ICF facility, so-called three zero criteria to assess the performance of flashlamp was presented, that is zero insulation, zero explosion and zero failure. We have done a lot to solve those problems and achieved zero insulation and zero explosion. Still there is a big gap between the current status and demand of ICF research. The goal of this dissertation is to investigate the failure mechanism of high power xenon flashlamp operated in ICF facility, optimize its performance as the pump source, and provide theoretical basis and experimental evidence for decreasing failure probability and improving pumping efficiency of flashlamp used in laser amplifer. This dissertation consists of the following six chapters. The first two chapters are literature summarization, experimental methods and theoretical calculation. The Chapter 3 to 5 are main parts and last chapter is conclusion. In Chapter 1, the basic characteristics and developments of xenon flashlamp as pump source are briefly introduced. After that, the failure mechanism and operation status of high power xenon flashlamps in ICF are reviewed. Thirdly, the purpose and research content of the dissertation are proposed. In Chapter 2, the experimental methods are introduced, including the high speed photography of discharge plasma channel, spectral distribution measurement, radiation efficiency measurement and reliability test method. Also the theory analysis of V-I characteristics, Trenholme model for pumping efficiency, and energy load limitation are presented. In Chapter 3, the evolution, profile character and influencing factors of discharge plasma channel are studied. By high speed photography and other measreing method the plasma channel profiles in flashlamp tube are captured and its initiation and development process is observed. The experimental results demonstrate that the initiation of plasma channel is random and unordered essentially. However, the electric potential distribution near the flashlamp influences the plasma channel characteristics the most significantly. The unique bifurcation phenomena and random distribution in multi-lamp arrangement are both determined by the external electric field. Though the higher discharge voltage will increase the effect of shockwave, it is helpful to improve the evenness, fullness and brightness of plasma channel. Besides, appropriate time interval between preionization and main pulse will affect the fullness of plasma column at the peak brightness. So there is chance to choose the optimized interval time to utilize this property. In Chapter 4, the thermal damage mechanism of lamp silica envelope and quartz solorization, and the electrode sputtering after a large number of shots are studied. High power xenon flashlamp for ICF facility are 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 appear in the inner surface of the quartz envelope opposite to metallic reflector inside amplifier. Scanning electron microscopy and X-ray photoelectron spectroscopy data demonstrate that the chemical composition of whitish participant is SiO2. The photographs of plasma channel indicate that the existence of metallic reflector beside silica envelope results in uneven distribution of plasma. The temperature is higher in the region with high plasma density. And that leads to local evaporation of silica glass and the whitening of quartz envelope. The SiO2 layer will attenuate radiation efficiency and raise the firing voltage and make flashlamp difficult to trigger. At the same time, the fluorescence intensity of Ce-doped quartz tube will decrease dramatically after thousands of shots. The mechanism is that the ultraviolet radiation and high temperature caused by discharge plasma make the Ce3+ element in tube body change into Ce4+. The measurement data of Ce-doped tungsten electrode shows that there are enriched zones of Ce atoms on the surface area of electrode after thermal activation process. And this enrichment effect is good for improve the electron emission property. The high speed photography and scanning electron microscopy demonstrate that there are many spots on the emission surface during discharge. And the erosion and micro-explosion phenomena have happened in course of discharge, which will result in sputtering and decrease the optical output of flashlamp. In Chapter 5, the optimization mechanism and performance of preionization and current-tail-cutting techniques upon high power xenon falshlamp are studied. The experimental data demonstrate that with proper time interval between preionization and main discharge, the radiant efficiency of flashlamps will increase by 3.8%~5.1%. While the interval is less than period of prepulse, the main capacitor will discharge the preionization circuit and the current through it oscillates badly. Meantime the radiant efficiency will decrease by more than 10%. In addition, the current-tail-cutting experiment is designed to study the influence on flashlamp performance. The data show that cutting tail after 300μs discharge, the total input energy can be decrease by 26%. Under this condition the energy load of flashlamp tube reduce dramatically and its operation life time raise effectively. In Chapter 6, all results of present dissertation are concluded. And the improvements and further work should be done in the future are also mentioned. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15877]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 刘建军. 大功率脉冲氙灯失效机理分析及性能优化研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
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