Ion extraction is a complex physical process with multi-particle interactions and multi-field coupling. Studies concerning the effects of different parameters on the ion extraction characteristics are helpful to optimizing the operating parameters of the ion extraction processes. A one-dimension electron-equilibrium fluid model is derived from the physical-mathematical model for the non-equilibrium plasma transport properties to describe the motions of each component in a metal ion extraction process. The reliability of the preceding physical-mathematical model, as well as the computer codes, is verified by comparing with the analytical solutions and experimental data. Based on this model, studies are conducted on the ion extraction characteristics of metal plasmas, including the spatial-temporal evolution of the space charge sheath, the ion extraction time, and efficiency under different operating conditions. The modeling results show that there exists significant shielding effect in the ion extraction process when the initial plasma density is high. The increase in the applied voltage and the electron temperature or the decrease in the electrode gap spacing will shorten the extraction time. Although there are no obvious differences between the ion extraction times with or without consideration of the resonant charge transfer, the resonant charge transfer process will cause the loss of the target ions.
KEY WORDS :ion extraction;electron-equilibrium fluid model;resonant charge transfer;parallel plate;sheath;
2)阶段Ⅱ(16.7 μs ≤ t ≤44.4 μs),数值解所获得的鞘层厚度变化比较缓慢,在27.7 μs的时间内仅增加了大约14.9%,这与文献[4]认为此时鞘层处于停滞状态基本一致。另外,数值解与解析解均表明此时等离子体中心区的离子数密度随离子引出时
图1
鞘层厚度及等离子体中心区离子数密度随离子引出时间的变化规律
Fig.1
Variations of the sheath thickness and ion density in the plasma quasi-neutral region with the ion extraction time
图2
离子引出时间随引出电压的变化规律以及归一化引出离子通量随时间的变化规律的数值解与实验对比
Fig.2
Comparison of numerical and experimental results on the variation of the ion extraction time with the externally applied voltage and that of the normalized ion extraction flux with time
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