大功率射频离子源驱动器等效阻抗特性分析

Analysis of equivalent impedance characteristics of a high power RF ion source driver

离子源是中性束注入系统的核心部件之一,射频离子源具备稳态运行的能力,成为未来中性束用离子源的主要备选源。在射频离子源中,阻抗匹配的合理设计和有效调谐是实现高功率稳定等离子体放电的核心,而驱动器的等效阻抗决定了阻抗匹配网络的设计,故对其特性的分析是必不可少的。基于射频等离子体变压器模型建立了射频离子源驱动器等效阻抗计算的解析模型,通过计算获得了驱动器等效阻抗随等离子体电子密度的变化特性,为阻抗匹配网络的合理设计及阻抗匹配调谐提供了参考。该模型能够较为快速准确地计算得出不同气压下驱动器内的电子温度,得出的不同气压和电子密度下的等效阻抗变化特性也与同类射频离子源的计算结果相符合。

[Background]The ion source is one of the key components of the neutral beam injection system.Radio frequency(RF)ion source has the advantages of long life time,easy maintenance and long pules operation,which make it the main alternative source for the neutral beam ion source in the future.[Purpose]This study aims to analyze equivalent impedance characteristics of a high power RF ion source driver with emphasis on the impedance matching network and effective tuning of matching network to achieve high-power and stable plasma discharge.[Methods]First of all,the analytical model was established on the basis of transformer model.The plasma conductivity was obtained by estimating the ohmic heating frequency and stochastic heating frequency in the plasma.Then,the equivalent impedance of the plasma was coupled to the excitation coils with the transformer model,and the equivalent impedance of the driver was obtained.Finally,parameters of the single drive RF ion source of negative ion based neutral beam injection(NNBI)system of Comprehensive Research Facility For Fusion Technology(CRAFT)were taken as example to calculate variation of equivalent impedance of actuator with plasma electron density by MATLAB code.[Results&Conclusions]Computation results show that the analytical model proposed in this study can be used to quickly and accurately calculate the electron temperature in the driver under different gas pressures,and the equivalent impedance under different gas pressures and electron densities,which provides a reference for the reasonable design and tuning of impedance matching network.