【作者】 陈志鹏；

【导师】 刘万东； 李弘；

【作者基本信息】 中国科学技术大学 ， 等离子体物理， 2010， 博士

【摘要】 本文研制了一种由多个碰撞条件下凹腔型射频感应耦合等离子体组合而形成的高密度,大面积均匀等离子体源。碰撞条件下的凹腔型感应耦合等离子体具有等离子体密度高的特性,但同时碰撞也限制了等离子体的扩散,破坏了其密度的均匀性。另一方面,碰撞条件下多个凹腔型射频感应耦合等离子体之间是独立的,而且多个凹腔型射频感应耦合等离子体之间会产生线性和非线性增强效应。因此我们将多个尺寸小巧的凹腔型射频感应耦合等离子体进行组合,来弥补碰撞条件下的密度不均匀性的缺点,研制出了的等离子体密度高达1018～1019m-3,面积为直径14cm,并可进一步扩展的等离子体源。本文研究了不同放电参数下,多个碰撞条件下凹腔型射频感应耦合等离子体之间的非线性增强效应,并给出理论模型。非线性增强效应是指多个放电线圈同时放电产生的等离子体密度大于各个放电线圈单独放电产生的等离子体密度之线性和。实验表明,多个放电线圈之间的非线性增强效应与等离子体密度和放电线圈的个数密切相关,与放电线圈的位型也有关系,而对中性粒子的密度不敏感,同时电子温度在多个线圈同时放电时基本保持不变。在双凹腔型射频感应耦合等离子体组合实验中,非线性增强效应随单个放电线圈在中心处产生的等离子体密度呈非单调变化,当密度达到某一恰当值时,密度比率可以高达2;而在四凹腔型射频感应耦合等离子体组合实验中,非线性增强效应在本文实验参数范围内随单个放电线圈在中心处产生的等离子体密度呈单调变化,在密度最小时密度比率可以高达4。考虑多步电离而建立起来的包含线性损失的非线性多步电离模型能够很好的模拟实验中出现的非线性增强效应。这表明在碰撞条件下凹腔型射频感应耦合等离子体中存在多步电离的非线性效应,这种效应使得多个放电线圈同时放电时出现非线性叠加增强现象。本文首次发现了碰撞条件下射频感应耦合等离子体中电磁波传输的反常趋肤效应。而反常趋肤效应和随机加热一直被认为是近似无碰撞射频等离子体中特有的现象。在本文的这部分工作中,首先详细介绍二维浸入式磁探针测量电磁场的技术问题,接着采用浸入式二维磁探针测量放电线圈周围的电磁场和传导电流分布。实验结果表明反常趋肤效应不仅仅在近无碰撞等离子体中存在,还同样存在于碰撞等离子体中。并且由于碰撞自由程和经典趋肤深度远远小于等离子体尺寸,第二电流层出现在等离子体主体区,而不是近似无碰撞环境下等离子体实验中的真空室壁附近。根据本文的实验环境,建立了一个用于描述碰撞等离子体中的反常趋肤效应的粘滞流体模型,其计算结果与实验结果符合的一致。本文在对碰撞条件下多凹腔型射频感应耦合等离子体组合性质的进行研究的同时,还提出了两种针对碰撞条件下等离子体的诊断方法。其中一种是针对本文实验环境而引入的“带悬浮极的单探针”。在这部分中,首先介绍了静电单探针在诊断等离子体方面的应用和计算电子能量概率分布函数的方法,重点通过探针测量回路模型,分析了多种因素对探针曲线和电子能量概率分布函数测量的干扰。提出在碰撞条件下凹腔型射频感应耦合等离子体中单探针诊断主要遇到的问题是真空室壁处的等离子体鞘层电阻不可忽略,并以此改良了普通单探针结构,加入悬浮极组成“带悬浮极的单探针”以克服该问题,实验和模型结果都表明其效果显著。除了静电探针诊断外,本文还利用电子和中性粒子弹性碰撞而发射出的连续光谱对等离子体进行了诊断。通过对连续谱辐射模型的简化,使得连续谱诊断方法变得易于操作并且可以独立测量碰撞条件下的电子温度和等离子体密度。实验中运用该方法对中等气压下射频感应耦合等离子体在不同放电参数(放电气压、放电功率)下的电子温度及密度进行了诊断,并将所得的结果与第二章中静电双探针测量的结果进行了比较。结果表明连续谱能够对中等气压下射频感应耦合等离子体中的电子温度进行很好的诊断,其结果与双探针测量结果基本一致。特别值得提出的是,本文还以能量传递为主线,逐步地总结和讨论了凹腔型感应耦合等离子体中的电磁波与等离子体之间的能量耦合、等离子体的产生和消耗、等离子体的扩散和输运等过程,形成一套完整的感应耦合等离子体基础理论,并在此基础上介绍了几个常用的理论模型。由于这部分内容较为繁琐,故以附录形式给出。本论文工作部分得到国家自然科学基金资助(Nos.10675121,10705028 and10605025),国家重点基础研究发展计划(No.2008CB717800)和国际热核聚变实验堆(ITER)计划专项(No.20096B107000)。更多还原

【Abstract】 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).更多还原