【作者】 甘宝霞；

【导师】 陈银华；

【作者基本信息】 中国科学技术大学 ， 等离子体物理， 2008， 博士

【摘要】 尘埃等离子体又称“复杂等离子体”,通常等离子体是由电子、离子和中性粒子组成,而尘埃等离子体除了上述的气体成分之外,还包含固体微粒。尘埃等离子体广泛存在于星际空间、行星环、慧尾、电离层以及地球上各种气体放电实验中,它具有许多新的特点,系统开放性、充电的变化、自组织及形成有序结构等,尘埃等离子体已经成为非常吸引人的研究领域。当等离子体中产生或投入大量尘埃颗粒时,由于电子的迁移速率远大于离子,到达尘埃表面的电子电流远大于离子电流,使得尘埃颗粒表面带有负电荷,等离子体中电子成分迅速减小,负离子的作用会凸现出来。负离子会影响尘埃颗粒的充电,从而影响尘埃颗粒表面的电势,而尘埃颗粒带电是尘埃等离子体与其它多离子成分等离子体的重要区别,因此研究负离子对尘埃等离子体的影响对于深入理解尘埃等离子体的性质有重要作用。尘埃等离子体中含有负离子称为电负性尘埃等离子体。本论文主要研究电负性尘埃等离子体中负离子含量对尘埃颗粒的振荡、尘埃晶格波和稳态尘埃空洞的影响。另外我们也研究了外加非均匀磁场对尘埃颗粒的振荡、晶格波的影响,这可能为尘埃等离子体的诊断提供一种新的方法。在第一章中,简要介绍尘埃等离子体的存在、特点、研究方法和研究进展。在研究进展中主要介绍了与本文研究方向一致的尘埃晶格波和尘埃空洞的研究情况。在第二章中,建立含负离子的一维射频碰撞鞘模型,研究鞘层的性质,自恰地解出鞘层电压和厚度随时间变化的规律,鞘层中电场电势的分布以及鞘层中各种粒子的密度及速度分布,研究了碰撞强度和负离子含量对鞘层结构的影响。研究结果表明,碰撞强度增大和负离子含量增加均会使鞘层极板电压增大,而使鞘层厚度减小,同时会使正离子的数密度增加而速率降低,并对结果作出了解释。在第三章中,在上一章鞘层模型的基础上,研究单个尘埃颗粒在含负离子的一维射频碰撞鞘中的运动,包括尘埃颗粒的充电、受力以及在鞘层中的振荡行为,尤其研究了各种作用力、负离子含量以及外加磁场对振荡行为的贡献。研究结果表明,中性粒子对振荡起阻尼作用,磁场对振荡频率的影响取决于具体的磁场构形和尘埃的平衡位置,负离子会降低尘埃颗粒的振荡频率,而振荡频率取决于颗粒的受力行为,因此负离子降低尘埃颗粒的振荡频率是源于负离子对于各种作用力的影响。在第四章中采用固体物理中研究晶格波的方法,对尘埃晶格波进行研究,包括一维链状晶格中传播的纵波、横波以及二维六角晶格中传播的横波。数值结果验证了近邻近似的正确性,也就是研究尘埃颗粒的相互作用时,只需考虑相邻颗粒之间的相互作用。采用了三种不同的电相互作用势模型,即屏蔽库仑势、Tsytovich及Wang模型对尘埃晶格波的色散关系进行比较。同时也研究尘埃间距、磁场强度和负离子含量对尘埃晶格波色散关系的影响。对于横波来说,加入吸引势会增加波的稳定性,而增大尘埃间距和增加负离子含量同样也会增加波的稳定性。但是对于纵波来说,以上的结果与横波是相反的。在第五章中对尘埃空洞的稳态结构进行研究。首先建立了电负性的一维稳态空洞的流体模型,负离子的存在会改变空洞内外区的Poisson方程以及空洞边界的充电方程的形式。数值研究了电离率和负离子含量对稳态空洞的影响。研究结果表明电离率的增加和负离子含量的增加均能使空洞边界减小,空洞内部的电场强度增加,马赫数增加。更多还原

【Abstract】 "Dusty Plasmas" is also called "complex plasmas", which contains not only electrons, ions, neutral particles in common plasmas, but also small solid particles. Dusty Plasmas exist widely in interstellar space, interplanetary space, planetary rings, comet’s tails, earth’s atmosphere, and all kinds of gas discharges in experiments. Dust plasmas have many unusual characters, such as open system, variation of charge, self-organized structure, etc. Now dusty plasmas have become a very interesting research field.In the study of dusty plasmas in laboratory, when many dust grains are immersed in gasous plasmas, because the electrons speed is much larger then the ions speed, the dust grains become negatively charged, the role of negative ions comes out as the content of electrons decreases quickly. Negative ions content will change the charge procession and the surface potential of dust grains, the latter distinguishes dusty plasmas from multi-component plasmas. The dusty plasmas contain negative ions are also called electronegative dusty plasmas. The influences of negative ions content on the oscillation of dust grain, lattice wave and dust void are mainly studied in this thesis. The influences of nonuniform magnetic field on the oscillation of dust grain and lattice wave are also studied. This may provide a new method for diagnostics.Firstly, the existence (also character, method, development) of dusty plasmas are introduced, particularly, the development of dust lattice wave and dust void which is related to my research work are introduced in detail.Secondly, one dimensional electronegative radio-frequency collisional sheath is built, and the characters of sheath are investigated. The sheath voltage and thickness vary with time, the space distribution of electric field, potential, the number density and velocity of all kinds of particles are solved self-consistently. The influence of collisional intensity and negative ions content on the sheath structure is studied. The result shows with the increasment of collisional intensity or negative ions content the sheath voltage increases and the sheath thickness decreases, the number density of ions increased and the velocity of ions decreased. Then the explanation of the results is given.Thirdly, on the basis of the sheath model above, the motion of an isolated dust grain is investigated, which includes the charge, forces and oscillation, especially the influence of the forces, the negative ion content and magnetic field on the oscillation. The result shows neutral particles contribute to damping. The influence of magnetic field on oscillation is decided by magnetic field structure and the equilibrium position. The negative ions will drop the oscillation frequency, which can be explained by the influence of negative ions on the ion drag force and electric field force.Forthly, using the method of studying lattice wave in solid physics, we investigate the dust lattice wave, including one dimentional longitudinal wave and two dimentional hexagonal transverse wave. Numerical result validates the neighbourhood approximation. Using three different electric interactional potential model (Coulomb Screen, Tsytovich, Wang), we compare the dispersion property of lattice wave. The influences of the inter-grain spaces, the magnetic field intensity and the negative ions content on the dispersion property are also investigated. For transverse wave, the attractive potential will increase the stability. Enlarging inter-grain spaces and increasing the negative ions content will also increase the stability. But it is contrary for longitudinal waves.Fifthly, the stable structure of dust void is investigated. A one dimentional electronegative hydro-dynamics model for stable void is studied. The existence of negative ions will change the form of Poisson equation inside and outside of the void and also change the charging equation at the void boundary. Numerical results show the influence of ionization rate and negative ions content on the stable void. The void boundary will decrease, the electric field intensity will increase and Mach number will decrease when raise the ionization rate or the negative ions content.更多还原