【作者】 赵鹏；

【导师】 樊明武； 陈德智；

【作者基本信息】 华中科技大学 ， 电气工程， 2018， 博士

【摘要】 中性束注入(NBI)是磁约束核聚变装置中等离子体辅助加热的主要手段之一。基于负离子源的NBI系统因其在离子束能达到1 MeV时仍然具有很高的中性化效率,被认为是未来大型磁约束核聚变装置的必然选择。大功率射频负离子源由于可长期无维护运行、结构简单等优点,于2007被国际热核聚变实验堆(ITER)计划选为参考离子源,近年来成为国际上聚变领域的研究热点。2011年,华中科技大学(HUST)在科技部ITER计划专项支持下,开展了“ITER高频负离子源激励器的关键技术与工程”研究,探索在低射频频率、低气压、大功率条件下的等离子体激发机理和技术,目前已初步建成了一个射频负离子源激励器实验平台(以下简称HUST源)。在低射频频率、低气压和大功率条件下的等离子体激发相对于常规的感性耦合等离子体(ICP)源难度更大,其中射频功率的利用效率成为一个突出的问题。本文以HUST源为研究对象,围绕射频功率的利用效率问题,重点关注线圈-等离子体射频功率耦合机理、在线阻抗匹配、射频功率与阻抗在线检测、等离子体参数诊断以及离子源控制等理论与工程问题。主要研究内容包括:(1)线圈-等离子体射频功率耦合特性分析采用解析模型和有限元模型对激励器线圈和等离子体之间的射频功率耦合特性进行了系统研究。探讨了等离子体参数、工作参数对于激励器阻抗和功率耦合效率的影响规律,为激励器的工作频率和气压的选择提供了依据。建立了包含法拉第屏蔽的激励器三维有限元模型,通过电磁场仿真分析,揭示了法拉第屏蔽抑制线圈-等离子体容性耦合的作用。(2)在线射频阻抗匹配研究面向大功率射频等离子体应用的工程实际,首次提出了频率和电容组合调节的在线阻抗匹配策略和自适应匹配算法。在线阻抗匹配策略以满足匹配应用要求、频率调节优先、减少调节电容为目标,通过跟踪阻抗变化可针对性地提供更快速有效的在线匹配调节方案。自适应匹配算法对常规的变量轮换法和梯度下降法进行综合和改进,在阻抗未知时,仅依据反射率自主选取匹配策略和优化匹配参数,相对于常规算法有效提高了自适应匹配速度和稳定性。(3)射频功率、阻抗在线检测系统研制研制了一套离子源运行时的激励器阻抗和功率在线检测装置。采用电容分压器和印制电路板(PCB)型罗氏线圈电流互感器对激励器线圈上的高频高电压、大电流取样,通过纯模拟信号处理的方法获取阻抗、功率等电参数。通过小功率(<1 kW)射频功率、阻抗在线检测实验,证明该系统具有较高的测量精度。(4)射频等离子体朗缪尔探针诊断系统研制针对大功率射频负离子源等离子体诊断,研制了具备高集成度和自动化程度的射频朗缪尔探针诊断系统。在扼流圈射频补偿的基础上增加补偿电极,降低了低频率下射频补偿的难度。通过自主开发的等离子体参数解读程序快速处理探针数据,自动获取等离子体参数,并研究了基于不同电子和离子收集理论的探针数据解读算法。(5)控制系统设计与实现离子源控制系统以PAC(Programmable Automation Controller,可编程自动化控制器)作为主控制器,采用分布式硬件架构和基于事件驱动+消息队列状态机+生产者/消费者模式的混合程序设计模式进行开发。系统结构紧凑,稳定可靠,扩展性强,顺利实现了HUST源射频等离子体激发与维持。(6)HUST源实验测试研究介绍了目前在HUST源实验平台上开展的实验和测试结果,包括工作参数检测、射频等离子体诊断和高压电源调试实验。本文工作为HUST源射频等离子体激发和检测提供了完整的技术实现手段并获得了丰富的离子源运行经验,也为后续开展完整射频负离子源研究奠定了基础。更多还原

【Abstract】 Neutral beam injection(NBI)is one of the main plasma heating methods in magnetic confinement fusion(MCF)devices.The negative ion source based NBI(N-NBI)is thought to be the inevitable choice for large-scale MCF devices due to its high neutralization efficiency even the beam energy reaches highly as 1 MeV.Due to the advantageous features of simple structure and principally maintenance-free in operation,the high-power RF negative ion source was chosen as the reference source of International Thermonuclear Experimental Reactor Project(ITER)in 2007 and has become one of the research focuses in fusion engineering field in recent years.Under the support of the Ministry of Science and Technology of China,Huazhong University of Science and Technology(HUST)has launched the project,“Key Technology and Engineering Research of Driver in the ITER High-frequency Negative Ion Source” since 2011,aiming to explore mechanisms and technologies of low RF frequency,low pressure and high power plasma production.Up to now,HUST has developed a test setup of RF ion source(HUST source)with successful plasma production.Plasma production at low RF frequency,low pressure and high power conditions faces much more difficulties than conventional inductively coupled discharges,of which utilization efficiency of the RF power is a key issue.This article takes the HUST source as the research object,focuses on the RF power utilization efficiency by studying the theory and engineering problems of coil-plasma RF power coupling mechanism,online impedance matching,online detection of RF power and impedance,plasma diagnostics and ion source control,etc.The main research contents are as follows:(1)Characterization of RF power coupling between the coil and plasmaAn analytical model and a finite element model are both employed to study systematically the characteristics of the RF power coupling between the coil and plasma in HUST source.Influences of plasma parameters and operating parameters on the driver impedance and power coupling efficiency are discussed,which could provide certain guidances for selection of the source operating frequency and pressure.A 3D finite element model of the driver containing Faraday screen(FS)is presented for electromagnetic(EM)simulation,which provides clear physical images of the EM fields in the driver and reveals the role FS plays in suppressing the capacitive coupling configuration in the source.(2)Online tuning of the matching networkFor the first time,online impedance matching strategies and an auto-matching algorithm combining both capacitance and frequency adjustments are presented for high-power RF plasma applications.The strategies aim to meet the requirements of matching performance,prioritize frequency adjustment and reduce capacitance adjustment,such that to provide faster and more efficient matching schemes according to the impedance variation in practical engineering applications.The auto-matching algorithm integrates and improves the typical cyclic variable method and gradient descent method,and embeds the function of selecting automatically the optimal matching strategy and optimizing the matching parameters based only on the the reflection coefficient when the impedance is not available.It improves effectively the auto-matching speed and stability compared to conventional algorithms.(3)Development of the online RF power and impedance detection systemAn online detection system for the driver impedance and RF power is developed in-house.A capacitive voltage divider and a PCB-type Rogowski coil current transformer(CT)are used to sample respectively the high-frequency,high coil voltage and large coil current.A purely analog signal processing method is used to process the sampling signals and obtain the RF power and impedance,which has fater response than conventional digital signal processing method.With low-power(< 1 kW)online RF power and impedance measurement experiments,this system is proved feasible with good measurment resolution.(4)Development of the RF Langmuir probe diagnostics systemA highly integrated and automatic RF Langmuir probe system for diagnostics of the plasma in HUST source are developed in-house.The addition of the compensation electrode to the conventional RF chokes reduces effectively the RF compensation difficulty at low RF frequencies.Through a plasma parameter interpretation program developed in-house,the probe data can be processed quickly and automatically to evaluate the plasma parameters.On the basis of that,different probe data interpretation algorithms based on multiple electron and ion collection theories are studied and compared.(5)Design and implementation of the ion source control systemThe ion source control system uses PAC(Programmable Automation Controller)as the main controller and adopts a distributed hardware architecture.A hybrid program pattern based on event structure,message queue state machine and producer-consumer pattern is presented to develop the control software.The system has a compact structure with good stability,reliability and strong expandability.Based on the control system,the plasma production at low RF frequency,low pressure,and high power conditions has been successfully achieved in HUST source.(6)Experimental and testing reasearch of HUST sourceThe experimental and testing campaigns performed on HUST source are introduced,including operationg parameters detection,RF plasma diagnostics and high-voltage power supply commissioning.In summary,this work provides a complete technical implementation scheme for RF plasma production and detection in HUST source.Meanwhile,lots of precious operating experiences for high power RF ion sources are obtained as well.Moreover,it lays the foundation for the follow-up research on the complete RF negative ion source.更多还原