电离层中释放六氟化硫效应的三维精细模拟研究

传统的六氟化硫电离层释放效应研究,一般建立的是点源释放模型,仿真结果精度有限.本文开展了电离层中释放六氟化硫的三维精细效应研究,在释放物扩散方程中加入了运载器飞行速度和姿态、释放物释放速度和流量、热层风场等参量对释放物扩散过程的影响;在等离子体扩散方程中考虑了地磁倾角和沿场扩散项对人工扰动结构等关键参数的影响,将二维等离子体扩散方程扩展到三维.同时,采用射线追踪方法,研究电离层人工扰动结构对短波传播路径的影响.本文的研究结果对研究电离层的动力学过程、电离层不均匀体的生成机制和演化规律有重要意义.     

几种典型化学物质的电离层释放效应研究

建立了一个包括中性释放气体扩散、离子化学反应及等离子体扩散等过程的化学物质电离层释放三维动力学模型,基于该模型构建了化学物质释放数值模拟软件平台,对H₂O,CO₂,H₂和SF₆等几种典型化学物质的电离层释放进行了数值模拟,给出了这些物质在电离层释放后产生的扰动特性和释放区域主要粒子的时空变化规律. 关键词： 典型化学物质释放 三维动力学模型 电离层扰动效应     

电离层中性气体释放的早期试验效应研究

在电离层释放电子吸附类中性气体能够引起电离层电子密度耗空,在释放之后快速形成"电离层洞";同时,由于释放气体的快速膨胀,挤压背景等离子体,在电离层洞的外边缘产生"壳状"电子密度增强结构,电离层洞和电子密度增强结构同时存在是释放早期试验效应的显著特征.本文研究了电离层中性气体释放的早期试验效应,建立了释放早期电子密度的时空演化物理模型,仿真了释放早期电子密度的时空演化过程,同时采用射线追踪方法研究了释放后10 s和120 s不同频率信号在扰动区的传播效应,并反演得到了电离层垂直探测电离图,反演结果与一次火箭喷焰的实际观测结果吻合较好,初步验证了本模型的正确性.     

强流电子束源阴极等离子体的粒子模拟

模拟了强流电子束源阴极表面附近区域数密度约1014 cm-3的等离子体的膨胀过程,观察到等离子体膨胀速度约为1 cm/μs。通过观察不同时刻阴极附近电子和离子的相空间分布、数密度分布和轴向电场分布,分析了等离子体膨胀过程。结果表明:等离子体的产生使得阴极表面电场增强,进而增大阴极的电流发射密度,电流密度增加使得空间电荷效应增强,并使等离子体前沿处的电场减小,当等离子体前沿处的电场减小到零时等离子体向阳极膨胀。讨论了等离子体温度、离子质量、束流密度和离子产生率对等离子体膨胀速度的影响。结果表明:等离子体的膨胀速度随着等离子体温度升高而增大,随离子质量增大而减小,但膨胀速度不等于离子声速;等离子体产生率越小,等离子体膨胀速度越小。     

电离层钡云释放早期动力学行为的数值模拟

在中性钡云扩散动力学模型的基础上,考虑钡原子的氧化和电离损耗, 探讨了钡云释放早期(t≤ 100 s)的演化基本特征、钡云形态、亮度以及电子密度分布等问题. 得到了不同释放量(1, 10 kg)、不同释放高度(250, 300 km)和不同初始形状因子(1, 10) 条件下钡云释放早期动力学行为的数值模拟结果.     

Compton散射下横等离激元与对等离子体作用特性

应用多光子非线性Compton散射模型、横等离激元色散方程和Karpman方法,研究了Compton散射对横等离激元与对等离子体作用特性的影响,提出了将入射超强激光和Compton散射作为横等离激元与对离子等离子体非线性作用新机制,给出了横等离激元非线性控制方程、等离激元数和能量公式。结果表明:与散射前相比,Compton散射使等离子体密度发生剧烈扰动,高频横等离激元与低密度扰动耦合非线性增强,导致横等离激元落入低密度区的几率增大。等离子体非线性频移和高密度区能量增加,低密度区能量减小,导致横等离激元电场包络迅速坍塌,等离激元数增加,场强度更强。     

电离层O~+83.4 nm日辉辐射传输特性研究

电离层极紫外波段(10～100 nm)日辉辐射主要是由太阳光电离激发以及光电子碰撞电离激发过程产生的,利用天基遥感探测手段对极紫外日辉辐射进行观测,可以获得白天电离层F层的电子密度、离子密度及空间分布等信息。极紫外波段日辉的天基遥感探测技术在国外起步较早,尤其是欧美、日本等国家,目前已经处于相对成熟的阶段。而我国对极紫外波段气辉辐射的研究几乎为空白,对电离层的探测也主要集中在夜间,如2017年我国发射的风云三号气象卫星D星上装载的电离层光度计可以获得夜间电离层峰值电子密度。对极紫外气辉进行遥感观测,特别是对电离层中O~+ 83.4 nm日气辉辐射的辐射特性进行探测,是获得白天电离层辐射特性的重要手段,也是国际上电离层光学遥感探测技术的研究热点。首先介绍了极紫外日辉的辐射传输理论,对日辉辐射的激发过程、碰撞过程以及共振散射过程进行了介绍,在此基础上重点分析了O~+ 83.4 nm日气辉辐射的产生机制及辐射特性。该辐射是太阳光电离激发低热层中的O原子而产生,为电离层极紫外气辉中辐射强度较强的信号之一, 83.4 nm气辉的高度分布情况可以提供电离层O~+密度扩线以及电子密度扩线,为白天电离层探测提供了一种有效手段。其次分析了O~+ 83.4 nm日辉辐射的谱带特性,以MSIS-00大气模型为基础,利用由美国计算物理公司与空军实验室联合开发的AURIC v1.2模型计算83.4 nm气辉辐射的初始体发射率、共振散射作用下的体发射率和临边柱辐射强度的分布情况,探究O~+83.4 nm日辉谱线与高度、纬度、太阳活动和地磁活动等电离层物理参量的相关性。基于极紫外日辉辐射算法,同时根据氧离子83.4 nm辐射传输特性,考虑该辐射的多次散射效应,提出了氧离子83.4 nm日辉辐射的计算方法。假设电离层呈现电中性,获得氧离子83.4 nm日辉强度可以反演白天电离层O~+密度,进而获得白天电离层F层电子密度的分布情况,为探究白天电离层特性提供了重要依据。     

等离子体性质对磁泡的影响

利用三维混合模拟程序计算了大量超热碎片离子在低密度背景等离子体中爆炸膨胀的过程.通过定量计算磁泡的变化过程和磁泡对碎片云运动的约束效果,分析了背景等离子体电荷密度、背景离子原子量、碎片离子荷质比等参数对磁泡的影响.计算结果表明,背景电荷密度对磁泡和碎片云的运动有重要影响.在碎片云扩张早期,背景离子原子量对磁泡扩张影响较小,但对后期碎片云的运动有一定影响.当碎片离子荷质比较小时,离子回旋半径大于磁泡半径,此时磁泡半径较小,且磁泡无法约束碎片云.当碎片离子荷质比较大时,离子回旋半径小于磁泡半径,如果此时背景电荷密度较低,磁泡和碎片云的早期扩张几乎不受碎片离子荷质比影响,但对系统后续演化有一定影响,如果此时背景电荷密度较大,碎片离子荷质比对磁泡和碎片云的运动有较大影响.     

托卡马克等离子体中共振磁扰动场放大效应对离子轨道特性的作用

首先,利用MARS-F程序模拟了HL-2A装置中不同电阻率、环向旋转频率和环向模数条件下等离子体对共振磁扰动(RMP)的线性响应过程,分析了不同情况下共振场放大效应对三维扰动磁场的影响;然后,利用Boris算法追踪了三维场作用下的离子轨道,并详细探究了不同扰动磁场改变离子轨道特性的物理机制.研究发现,考虑等离子体响应后的扰动磁场可增强离子轨道径向展宽,且轨道最大径向展宽随轨道上扰动磁场平均值的增大而增大;同时,离子在通过扰动磁场被强烈放大的区域时轨道径向展宽会显著增加.该物理机制可用于解释RMP缓解边界局域模实验中离子直接损失增加和等离子体径向输运增强现象.     

高温稠密等离子体的分子动力学模拟

将平均原子模型和密度泛函理论相结合,发展了一个计算高温稠密等离子体中离子之间平均相互作用势的理论模型. 利用平均原子模型考虑了高温稠密物质中电子的激发和密度效应对电子结构的影响,利用动能和交换相关能的局域密度泛函近似计算离子之间的平均相互作用. 基于发展的相互作用势模型,开展了分子动力学模拟,研究了高温稠密Al和Fe等离子体的状态方程.     

Atomic collision processes relevant for heavy ion beam probes

Atomic collision processes of fast Tl and Cs ions with particles in a high temperature fusion plasma are investigated. At low beam energies (<5 MeV), ion impact collisions and charge exchange processes can be neglected compared to electron ionization processes. At beam energies above 5 MeV and high plasma ion temperatures, collisions with ions start to contribute significantly to signal generation and attenuation. Also, collisions with the neutral background gas in the beamlines can attenuate the ion beam significantly and lower the signal level, if the vacuum pressure is above 10^-4 Torr. For the heavy ion beam probes operating today, only electron impact ionization processes are important and accurate predictions of the secondary signal level and electron density profile measurements are possible because of the good knowledge of electron impact ionization cross sections for Cs ⁺ and Tl⁺ ions     

Influence of a centered dielectric tube on inductively coupled plasma source: Chamber structures and plasma characteristics

A high-density RF ion source is an essential part of a neutral beam injector. In this study, the authors attempt to retrofit an original regular RF ion source reactor by inserting a thin dielectric tube through the symmetric axis of the discharge chamber. With the aid of this inner tube, the reactor is capable of generating a radial magnetic field instead of the original transverse magnetic field, which solves the E × B drift problem in the current RF ion source structure. To study the disturbance of the dielectric tube, a fluid model is introduced to study the plasma parameters with or without the internal dielectric tube, based on the inductively coupled plasma(ICP) reactor. The simulation results show that while introducing the internal dielectric tube into the ICP reactor, both the plasma density and plasma potential have minor influence during the discharge process, and there is good uniformity at the extraction region. The influence of the control parameters reveals that the plasma densities at the extraction region decrease first and subsequently slow down while enhancing the diffusion region.     

The role of O+ ions in channeling solar wind energy tothe ionosphere

In space weather prediction, the transport of solar wind energy through the magnetosphere is a major aspect. For the transport of energy from the magnetosphere to the ionosphere, magnetic field-aligned (Birkeland) currents are a very important agent. The authors discuss the role of O⁺ ions for driving field-aligned currents of spatially alternating polarity that may explain multiple auroral arcs. It is known from earlier work that nonadiabatic motion of O⁺ ions in the magnetotail plasma can lead to the formation of density striations that are stationary in the GSM frame. As the magnetospheric plasma drifts through these density striations, magnetic field-aligned currents of alternating signs are forced to flow in and out of the oxygen-rich region to maintain quasineutrality. This generates Alfven waves that propagate in the drifting plasma but can form stationary structures in the GSM frame. As the currents close in the ionosphere, the equatorial plasma constitutes a generator from which spatially alternating magnetic field-aligned currents carry energy to the ionospheric load. The wavelength of the density striations, mapped to the ionosphere, is compatible with the spacing of stable auroral arcs, and the power supplied by the equatorial generator region is estimated to be compatible with what is needed to drive auroral arcs. Thus, the consequences of nonadiabatic motion of O⁺ ions may explain how part of the energy extracted from the solar wind is channelled into multiple auroral arcs     

Beam Probe Space-Potential Measurement in a Minimum-B Field

A measurement of plasma space potential in a minimum-B magnetic field has been made with a particle beam probe. The diagnostic technique is an extension of conventional heavy ion beam probing in that, among other features, the probing beam is neutral rather than ionized cesium and the parallel-plate electrostatic energy analyzer is fully characterized in a new manner which permits its use in complex magnetic confinement geometries.     

The effect of many-electron correlations on the alignment of ions in atomic photoionization

It is shown that the inclusion of many-electron correlations and electron shell rearrangement can significantly change the alignment of the ion arising from the photoionization of atomic subshells with $\text{j >}\text{1}\text{2}$. The degree of alignment for photoionization of the 4d¹⁰ subshells of Xe, Cs and Ba atoms and the 5p⁶ subshell of Ba is calculated.     

电子回旋共振等离子体密度均匀性的数值研究

基于漂移扩散近似,在轴对称假设下,对电子回旋共振等离子体源腔室内的等离子体建立了二维流体模型.采用有限差分法对所建立的模型进行了自洽数值模拟,得到了等离子体密度均匀性随时间演化的数值结果.通过对数值结果的分析,研究了背景气体压强、微波功率和磁场线圈电流对等离子体密度均匀性的影响.研究表明,在电离初期,电子密度的均匀性好于离子密度的均匀性.在电离后期,离子密度的均匀性好于电子密度的均匀性.随着背景气体压强的增大,电子密度和离子密度的均匀性都在增加,且离子密度的均匀性增加的更快.随着微波功率的增大,电子密度和 关键词： 等离子体密度均匀性 背景气体压强 微波功率 磁场线圈电流     

Charge accumulation layers and surface states in ultrathin Cs,Ba/n-GaN(0001) interfaces

It is found that ultrathin cesium and barium coatings radically change the electronic properties of the surface and the near-surface region of epitaxial n-GaN(0001) layers. A charge accumulation layer serving as a quasi-two-dimensional electronic channel is first formed by adsorption on the surface of a semiconductor. It is revealed that photoemission from the accumulation layer is excited by visible light from the transparency region of GaN and is characterized by a high quantum yield. It is found that the photoemission thresholds hν _s and hν _p for s-and p-polarized excitation are equal to each other and correspond to the work function. The lowest work function for Cs,Ba/n-GaN interfaces is observed at Cs or Ba coverages close to 0.5 monolayer. Two bands induced by the local interaction of cesium (barium) adatoms with gallium dangling bonds are detected in the electronic spectrum of surface states of Cs,Ba/n-GaN interfaces. An oscillation structure is observed in spectral dependences of the photoyield. This effect is new for photoemission. A model of the effect is proposed. It is found that electronic and photoemission properties of the interfaces correlate with the structural perfectness of the epitaxial n-GaN(0001) layers.     

Collisionless Plasma Expansion in the Presence of a Dipole Magnetic Field

The collisionless interaction of an expanding high–energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfvén–Mach numbers using the particle–in–cellmethod. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)