【作者】 李现涛；

【导师】 孙继忠；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2011， 硕士

【摘要】 氢气等离子体在材料处理、核聚变以及高能物理方面具有广阔的应用前景。尤其是在核聚变方面,氢气等离子体作为核聚变中性束加热的主要反应物质,无论在实验和理论方面,还是在模拟研究方面都得到了深入地研究。随着聚变装置尺寸的增加,中性粒子的能量要达到1 MeV量级；而在此能量下,正氢离子的中性化率几乎为零,因此中性束加热必需采用负氢离子源。如何利用体积源生成机制,高效生成负氢离子是目前负氢离子源研究急需解决的问题之一。本文的目的是探索高效产生负氢离子的途径。本文第一章简要地介绍了等离子体的一些基本性质以及本文的研究背景。在第二章中本文对一维静电PIC-MCC模型的实现方法进行了详细地描述。在第三章中,本文主要应用PIC-MCC模型模拟了平板电极的低气压容性耦合氢气等离子体。放电电极由射频电源和脉冲电源双电源驱动,从而使得两种电源的优势互补：射频电源维持放电的持续进行,而脉冲电源用来调节等离子体中电子的温度,并且提高等离子体的密度以及高振动激发态氢气分子的产生率。文中分别对单电源的射频放电和双电源放电等离子体特征进行了研究和讨论。在单电源的射频放电中,模拟很好地展现出了等离子体中电子的振荡现象以及鞘层的形成过程,并且可以观察到在低气压容性放电中典型的随机加热过程—电子能量的双温分布现象。在射频电源和脉冲电源共同驱动的双电源放电中,我们主要模拟了电子能量和密度随时间的演化过程,从而更好地呈现出脉冲电源在这种双电源放电中的作用。模拟发现,该高短脉冲电源可以很好地调节电子的能量：在脉冲电压开启和结束的最初阶段,电子的能量远高于在单电源射频放电中的电子能量；在脉冲电压的坪区,电子能量明显地降低,但仍高于单电源时的电子能量；在脉冲电压关闭后,随着时间的推移,电子的能量逐渐地降低到单电源时的能量值,但是,在最初的一段时间内,电子平均能量随时间变化的曲线出现一些明显的振动现象,随着时间的推移,电子能量振动的峰值逐渐降低,并且最终消失。放电中的高振动激发态氢气分子的产生率出现了类似的现象。本文对这些有趣的现象进行了详细地解释：这些现象主要是由于高短脉冲电压形成的极强的电场造成的,这种极强的电场迅速产生和消失的过程对等离子体中电子能量和密度的空间分布造成很大的影响,从而出现了上述现象。因此,本文证实了在双电源容性耦合放电中脉冲电源能够调节电子能量和提高等离子体密度以及高振动激发态氢气分子的产生率。更多还原

【Abstract】 Hydrogen plasmas are widely used in material technology, nuclear fusion and high-energy physics. Especially in the nuclear fusion field, hydrogen plasmas used as the main reaction materials in the neutral beam heating reactor have been intensively studied in relevant theoretical, experimental and simulation aspects. Especially, negative hydrogen ion sources are particularly indispensable for the neutral beam heating in the future fusion reactors because of the high neutralization efficiency of negative hydrogen ions in the MeV energy range in which the neutralization efficiency of positive hydrogen ions is almost zero. One of the most important problems we have to solve is how we can produce the negative hydrogen ions efficiently via the volume production. In this paper, we use the PIC-MCC model to search for the way of producing the negative hydrogen ions more efficiently.In Chapter one, we briefly introduce some basic characters of the plasma and the relevant backgrounds of the paper. In Chapter two, the one-space-dimension and three-velocity-dimension electrostatic PIC-MCC (Particle-in-Cell with Monte Carlo collision) method used in this paper is described detailedly. In Chapter three, the PIC-MCC model is used to investigate the low pressure capacitively coupled hydrogen discharges driven by combined radio frequency (rf) and pulse sources. The rf source is used for providing the necessary electrons to maintain the plasma, while the high and short pulse source is used for modulating the electron energy and enhancing the plasma density and the production rate of highly vibrationally excited hydrogen molecules. The characters of the plasma driven by single rf source and dual-source are described respectively.In the single rf source discharge, the simulation displays the electron oscillations and the formation process of the plasma sheath. In the same time, it shows that the electron energy distribution functions (EEDF) is approximately two temperature distribution, which is the typical character of the stochastic heating mechanism in low pressure capacitively coupled plasmas.In the dual-source discharge, we display the spatiotemporal evolutions of the electron energy and density respectively to show the effect of the pulse source in the discharge. The simulation results show that the short and high pulse source can modulate the energy of electron effectively:in the early and late pulse-on time, the electron energy increases rapidly to a very high value, which is much higher than that in the single rf source discharge; during the plateau time, the electron energy drops rapidly to a low value, but it is still higher than that in the single rf source discharge; in the early pulse-off time, a few peaks of attenuated electron energy appear periodically; as time goes, these peaks become weak, and disappear gradually. Similar phenomena can be found in the production rate of highly vibrationally excited hydrogen molecules. In the paper, we discuss these phenomena detailedly. The phenomena are mainly caused by the strong electric field which is induced by the high and short pulse source. The rapid formations and disappearances of the strong electric field greatly influence the electron energy and density distributions in the discharge space, and then cause the above phenomena. The simulated results demonstrate that in the dual-source capacitively coupled discharges, the short and high pulse source can modulate the electron energy and increase the plasma density and the production rate of highly vibrationally excited hydrogen molecules effectively.更多还原