激光触发真空开关的初始等离子体特性及其优化设计方法研究

The laser triggered vacuum switch may be an advanced high-voltage and heavy-current pulse switch. It will be capable of switching on heavy current, be convenient of isolating trigger system, be easy of triggering the switch with certain frequency, be less of trigger delay time and jitter time. However, the initial plasma characteristics are significantly differences between the laser trigger and the electrical pulses trigger. Few related study was reported in overseas and domestic. The research has just got started and is far from sufficient. The plan of this proposal is to carry out a lot of investigation experiments and theory analysis with a self designing laser triggerering vacuum switch model. Our main work will focus on the initial plasma characteristics of laser trigger and its optimizing design method. it includes the interaction relationship of laser light field and trigger material, the developping process of initial plasma, the initial process of the main arc, as well as the experimental and theoretical research of the impact factors and the impact mechanism. In order to meet requirement of laser miniaturization, studies involve the optimization design method among the material structure of laser trigger, the laser light path and types of focusing, laser waveform parameters of the laser trigger, which can reduce the required laser energy as much as possible. The subject of research will reveal the initial plasma characteristics of laser triggerering vaccum switch and its conduction process mechanism which may help others get depth understanding and application to the principle of vacuum laser trigger. Finally, it will provide a basis for research and guidance to laser miniaturization and the applications research of the laser trigger in the triggered vacuum switch.

激光触发真空开关将可能是一种先进的高压强流脉冲开关，将具有通流容量大、触发机构隔离与重频触发控制方便、触发时延抖动小等显著优势。但激光触发的初始等离子体特性与电脉冲触发的初始等离子体特性有着显著的不同，国内外的相关研究报道不多见，研究刚刚起步，很不成熟。本课题将以自行设计的激光触发真空开关为对象，研究激光触发的初始等离子体特性及其优化设计方法，包括激光光场与触发材料的相互作用与关联关系、激光触发初始等离子体发展过程、主间隙引弧过程以及有关影响要素与影响机制等的实验与理论研究。针对配套激光器小型化要求，对激光触发材料结构、激光光路与聚焦方式、激光波形参数等进行优化设计方法研究，尽可能地降低需要的激光触发能量。本课题的研究可揭示真空激光触发开关的初始等离子体特性及其导通过程机理，有助于人们对真空激光触发原理的深入认识与应用，对配套激光器小型化、激光触发真空开关的应用开发研究提供基础与指导。

高压强流开关在脉冲功率系统中起着至关重要的作用，激光触发真空开关既可具有电触发真空开关通流容量大、欠压比小等优点，又可具有激光触发机构隔离方便、触发时延大为降低等显著优势，但激光器及其光学系统的昂贵使得其应用与开发研究停滞不前。本项目针对激光器小型化目标，就激光光场对触发材料的作用机制与影响因素、激光参数对触发初始等离子体的影响规律、激光触发的燃弧特性进行了全面研究；对激光触发材料与结构、激光光路与聚焦方式、激光波形参数等方面进行了优化分析，提出了相关优化设计方法。主要结果：（1）研究了激光光场对触发靶材的作用机制。提出并建立了激光光场对触发靶材的局部加热汽化理论计算模型，实验研究了激光光场对触发靶材的加热汽化效应，实验与理论计算结果具有较好的一致性；（2）研究了初始等离子体发展与开关导通过程。建立了开关导通及其稳定条件的计算模型，实验发现了电弧电压噪声在大电流下出现的时间前移缩短的规律；建立了基于阴极斑点理论的触发时间计算模型，可以近似计算出激光触发真空开关的导通延迟时间，实验结果与理论计算结果相一致；（3）研究了激光及其调制对开关触发特性的影响。理论分析与实验发现，被动调Q模式能显著降低开关导通的触发能量和减小激光器体积与造价；理论分析与实验结果表明，不同激光偏振态对电离速率和电子剩余能量有明显的影响，发现圆偏振光可以使开关导通时延显著降低；研究了脉冲波形对触发导通特性的影响，发现共线结构的双脉冲比总能量相同的单脉冲能形成强度更大的电离线状谱线，从而使开关导通时延显著降低；（4）以上述研究为依据，对激光触发真空开关的光路和触发材料进行了优化分析，结果表明，开关最低触发能量可从一般的大于10mJ降低至0.3mJ，而导通时延可从一般几百ns降低至17ns，相应的抖动可在10ns以内。研究成果对于激光触发真空开关的进一步应用与开发研究具有重要参考意义。