Cobination Of Multiple Internal Inductively Coupled Plasma Sources And Anomalous Skin Effect In Collisional Environment

In order to produce a high-density and large-area plasma, multiple internal inductively coupled plasma(ICP) sources have been constructed at intermediate gas pressure. Experimental results indicate that the inherent bad radial uniformity of plasma density in single internal ICP source could be improved by the combination of multiple sources. Furthermore, it is discovered that a remarkable nonlinear enhancement phenomenon of plasma density exists in the combination, where the plasma density distribution in combination is larger than the linear summation of that in every individual internal ICP source. In an array of four internal ICP sources, the plasma density in the region among these antennas is significant as high as5×1018m-3. The area of this region, limited by the chamber volume in our experiment, achieves 14cm in diameter and could be enlarged if in a bigger one. Base on the experimental data and analysis, a principle is also given to produce a dense plasma in a larger area by more internal ICP sources.The nonlinear enhancement of plasma density in a combination of two and four collisional internal ICP sources has been experimentally investigated at different mediate gas pressures and rf powers, where each source can be considered as independent and the combination is linear. In the nonlinear enhancement phenomena, the plasma density distribution in combination is not only larger than that of every individual source, but also remarkable larger than the linear summation of them in most region of the midplane. The nonlinear enhancement effect in the centre of the midplane has stronger functional relation to the plasma density and is sensitive to the arrangement method, while it is weakly affected by the neutral particle density. Meanwhile, the electron temperature approximately keeps constant during the antenna's individual to combinational discharge. Furthermore, a nonlinear diffusion model including the multi-step ionization and linear effective loss is applied to describe the nonlinear enhancement phenomena in linear combination, of which the solutions is good consistent with the experimental results.Anomalous skin effect is usually a particular phenomenon in nearly non-collisional plasma environment; however it also exists in the collisional internal ICP in our experiment. The radio-frequency electromagnetic field and induction current are measured with an immersed two-dimension magnetic probe, after the technical details of this kind of probe have been introduced. The experimental result indicates the fact that the nonlocal phenomenon exists in the collisional plasma discharge, where the second current layer appears in the plasma bulk, rather than near the chamber wall in the non-collisional environment, deriving from that the free length and the classic skin depth both are much smaller than the plasma size. According to our experimental condition, a simplified fluid model with viscosity is calculated to depict the anomalous skin effect. Its result approves that the nonlocal phenomenon will also emerge in the collisional environment excluding the effect of the chamber wall.In this article, two kinds of diagnostics in collisional plasma are developed. One is the classic electrostatic single probe, from which the measurement of the electron energy distribution function could be inferred. With the help of the circuit model of the single probe and the probe characteristic expression, the impact of the circuit on the measurement of EEDF has been calculated and discussed in theory. From the analysis, the collision brings up the lack of plasma density in the chamber wall, which is leadingly responsible for the distorted single probe curve. A modified single probe with a floating tip is invented to overcome the problem above, and its validity has been exhibited in theory and experiment.The other is the continuous emission spectrum analysis. A simplified model for the physical mechanism of continuous emission in this kind of plasma is developed to analyze its spectrum, and the validity of this model is discussed in a wide range of discharge parameters including the electron temperature and ionization degree. According to the simplified mode, the continuous emission spectrum in a collisional argon internal inductively coupled plasma is experimentally measured to determine the electron temperature distribution at different gas pressures and rf power. At the same time, inverse Abel transform is applied for a good spatial resolution. The result of the continuous emission spectrum analysis is compared with that of the electrostatic double probes, which indicates the effectivity of this method.In the appendix, the energy coupling between rf electromagnetic field and plasma, the generation and loss of plasma, the diffusion and transport of plasma are introduced step by step with the energy flow process. Base on the introduction, some ICP models are discussed at last.This project was supported by National Natural Science Foundation of China (Nos.10675121,10705028 and 10605025), National Basic Research Program of China(No.2008CB717800) and ITER program special of China(No.2009GB 107000).