【作者】 陈鹏；

【导师】 陈德智； 李冬；

【作者基本信息】 华中科技大学 ， 电气工程， 2023， 博士

【摘要】 大功率射频负离子源是磁约束核聚变装置中性束注入系统的核心部件。为了获得所需的负离子束流参数,高达数十至上百千瓦的射频功率被馈入离子源激励器并耦合进等离子体。功率转移效率和线圈电压等激励器电特性参数是射频功率转移过程的重要表征。提高射频功率转移效率,降低线圈电压,对大功率射频负离子源的高效可靠运行至关重要。然而,离子源激励器电特性的物理机制还不尽清楚,其建模方法和测量方法有待发展,法拉第屏蔽设计和放电条件优化也都缺乏理论指导。本文依托于华中科技大学(HUST)负离子源实验平台,对大功率射频负离子源激励器电特性开展建模仿真与实验研究。主要研究内容如下:(1)通过分析激励器等离子体的功率耦合相关特性,建立了等离子体的等效有损介质模型,考虑了射频功率耦合的波特性,开发了三维有限元电模型方法,评估激励器电特性精度优于现有其他电模型方法。由于同时考虑了等离子体的导电和介电特性以及等离子体的不均匀空间分布,显著提高了有限元电模型的精度;评估误差主要来自所使用的简化随机加热模型和没有考虑磁化的影响。(2)采用电磁-流-热-结构多物理场耦合分析,研究了法拉第屏蔽结构参数和材料对激励器电特性以及温升、形变等的影响,为法拉第屏蔽结构设计和材料选取提供理论支持。在所研究参数范围内,激励器损耗等效电阻与法拉第屏蔽壁厚近似线性正相关,与电导率平方根的倒数近似线性正相关;相同的通透率下,缝宽和缝数对耦合的影响不同;温度升高也会引起损耗增大,功率转移效率降低。考虑温升,钼的形变约为铜的一半,不锈钢的形变与铜基本相同。(3)建立了带隔离变压器Γ型匹配网络的含寄生阻抗互感耦合电路模型,开发了通过测量匹配网络前电参数基于匹配模型得到激励器电参数的间接测量方法,避免了在高压、强流、强射频干扰在线运行环境中安装高相位差精度电压电流传感器的困难。应用于HUST大功率射频负离子源,间接测量结果与直接测量结果相对偏差<10%,精度满足工程要求。结合有限元电模型方法,分析了相减法用于估测HUST大功率射频负离子源射频功率转移效率的有效性。(4)依托于能够模拟大功率射频负离子源结构与放电条件的小型感性耦合等离子体实验装置,实验研究了工作气压、射频频率等放电条件对激励器电特性的影响规律,为理解离子源工作特性、优化工作参数提供参考。工作气压从0.1 Pa升高到6.6 Pa,等离子体密度和射频功率转移效率变化趋势相似,均先增后减,而线圈电压先减后增,在约1 Pa到3 Pa之间出现极值。工作频率从1 MHz提高为2 MHz,射频功率转移效率和线圈电压都增大,但在相同的等离子体吸收功率下,产生的等离子体密度几乎相同。更多还原

【Abstract】 The high-power radio-frequency(RF)negative ion source is the core component of a neutral beam injection system in large-scaled magnetic confinement nuclear fusion devices.To obtain the required negative ion beam,RF power of tens to hundreds of kilowatts is fed into the driver of the ion source and coupled into the plasma.The electrical characteristics of the driver,such as the power transfer efficiency and the coil voltage,are important characterizations of the RF power transfer process.Improving the RF power transfer efficiency and reducing the coil voltage is crucial for the efficient and reliable operation of high-power RF negative ion sources.However,the physical mechanism of the electrical characteristics of the driver is not fully clarified.The modeling and measurement methods for the electrical characteristics need to be developed.And there is a lack of theoretical guidance for the design of the Faraday shield and optimization of discharge conditions.Relying on the negative ion source experimental setup of Huazhong University of Science and Technology(HUST),modeling and experimental research on the electrical characteristics of the driver are carried out in this thesis.The content is as follows:(1)By analyzing the power coupling characteristics of the plasma in the driver,an equivalent lossy dielectric model of the plasma was established,and the wave characteristic of RF power coupling was considered.A three-dimensional finite-element(FEM)electrical model method with better accuracy than other existing electrical model methods was developed.By considering the conductivity and dielectric properties of the plasma,and using the input conditions that reflect the plasma inhomogeneity,the accuracy of the FEM electrical model has been significantly improved.The remaining error is mainly due to the simple stochastic heating model and the neglect of magnetization.(2)By the electromagnetic-fluid-thermal-structural multi-physics analysis,the effect of the structures and materials on the electrical characteristics of the driver,as well as the thermal-mechanical performances of the Faraday shield,was studied.It helps the structural design and material selection of the Faraday shield.Within the studied parameter range,the loss equivalent resistance of the driver is approximately linearly positively correlated with the wall thickness and the reciprocal of the square root of the conductivity.The influence of slit width and slit number,with the same slit area,on the RF coupling is different.As temperature increases,the losses increase,and RF power transfer efficiency decreases.The deformation of molybdenum is about half that of copper,while the deformation of stainless steel is roughly the same as that of copper.(3)A mutual inductance coupling circuit model considering the parasitic impedance was established for the transformer-isolated Γ-type matching network,and then an indirect measurement method was developed which uses the electric parameters measured before the matching network and the matching model to obtain the electrical parameters of the driver.It avoids the difficulty of installing current-voltage sensors with very high phase(difference)accuracy in the on-line environment with high voltage,large current,and large RF interference.Applying this method to the high-power RF negative ion source developed by HUST,the relative deviation between indirect measurement results and available direct measurement results is smaller than 10%.The accuracy of the indirect measurement method meets engineering requirements.With the help of the FEM electrical model method,the effectiveness of the subtraction method for measuring RF power transfer efficiency is verified.(4)A small-scaled inductive coupled plasma experimental device whose structure and discharge conditions are similar to those of high-power RF negative ion sources has been developed.The influence of discharge conditions such as working pressure and RF frequency on the electrical characteristics of the driver has been experimentally studied.It provides a reference for understanding the working characteristics of ion sources and optimizing the working parameters.As the working pressure increases from 0.1 Pa to 6.6Pa,both plasma density and RF power transfer efficiency first increase and then decrease,while the coil voltage first decreases and then increases.The extreme point is between approximately 1 Pa and 3 Pa.When the driving frequency increases from 1 MHz to 2MHz,both RF power transfer efficiency and the coil voltage increase,but the plasma density is almost the same under the same plasma power.更多还原