不同释放高度的化学物质的电离层扰动特性

在电离层释放H₂O, CO₂, H₂和SF₆等中性气体能导致释放区域电子损耗, 形成明显的人工电离层洞, 是电离层人工变态的重要而有效的手段之一. 本文在改进电离层化学物质释放三维动力学模型的基础上, 对不同释放量级的H₂O 和SF₆在不同释放高度下产生的电离层洞形态结构及其时空演化规律进行了系统对比研究, 探讨了释放高度对化学物质释放电离层扰动效果、电离层洞形态及其动力学特性等的影响, 并对其成因进行了分析. 关键词： 化学物质释放 电离层扰动 人工电离层洞 三维动力学模型     

人工电离层洞形态调制及其对短波传播的影响

本文在电离层中性气体点源扩散近似解的基础上,给出了多源释放动力学模型.分析了释放物质、释放高度、释放模式和释放量等因素对人工电离层洞形态调制的影响,并利用电离层短波三维数字射线追踪技术,对不同调制电离层洞的电波传播效应进行了数值模拟和分析. 关键词： 化学物质释放 人工电离层洞 形态调制 电波传播效应     

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     

非球对称电离层掩星数据反演

电离层掩星数据的传统反演方法是电离层球对称假设下的Abel变换反演方法,但是实际的电离层电子密度分布不是球对称的,电离层的非球对称分布给电离层电子密度反演带来误差.发展了一种新的非球对称电离层掩星反演方法,利用国际参考电离层模型提供的三维电离层电子密度分布先验信息来修正掩星总电子含量 ,再通过球对称假设下的Abel变换反演出电离层电子密度.利用新方法反演了星座气象、电离层和气候观察系统掩星实测数据,并将得到的反演结果与电离层探测器资料进行了比较.结果表明,新方法能够较好地反演出电离层电子密度. 关键词： 电离层掩星 电子密度 国际参考电离层模型     

基于化学物质释放的电离层闪烁抑制方法研究

中低纬地区经常发生的电离层闪烁,严重影响卫星链路的无线电信号传播过程,导致卫星通信导航信号质量下降,甚至中断.在电离层闪烁发生前的酝酿生成期,通过向电离层闪烁"种子因素"的等离子体泡内释放电子密度增强类化学物质,填充等离子体泡,改变等离子体环境特性,调控电离层动力学过程,能够降低电离层等离子体不稳定性增长率,进而抑制闪烁的发生.本文开展了基于化学物质释放的电离层闪烁抑制理论及方法研究,根据化学物质释放对电离层等离子体环境的影响,定量计算控制因素改变对不稳定性增长率的贡献,建立了基于电子密度增强类化学物质释放的电离层闪烁抑制物理模型,仿真了等离子体泡的填充过程及等离子体不稳定性增长率的演化过程.仿真结果表明该方法具有较好的闪烁抑制效果,为我国中低纬地区卫星信号电离层闪烁抑制研究奠定了理论基础.     

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.     

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.     

钡和铯释放的电离层扰动效应对比

碱金属或碱土金属在电离层释放后,迅速在太阳辐射作用下发生光电离,产生正离子和电子,形成人工等离子体云团.本文基于三维双成分流体模型,考虑释放区域水平风场的影响,探讨了钡和铯在电离层释放后的时空演化规律,并对钡和铯的电离层扰动效应进行了对比.模拟结果表明,不考虑中性风场时,生成的等离子体云团逐渐沿磁场被拉伸成椭球形结构,同时,膨胀的等离子体云会推开背景氧离子,在释放中心形成氧离子密度空洞,并在两侧产生两个对称的密度尖峰;水平风场的存在会使得生成的离子云逆风侧的密度梯度变陡,释放物质对背景氧离子的扰动也更大;对比钡与铯的释放结果发现,由于铯的扩散系数较小,钡云的膨胀更为迅速,Ba+云团的覆盖区域更广;而由于光电离率较大,释放相同质量下铯的离子产率更高;此外,Cs+的扫雪机效应比Ba+扫雪机更强,氧离子密度空穴和凸起处的扰动也更大.     

COSMIC掩星电离层资料反演以及结果验证

通过COSMIC掩星电离层观测资料L1和L2相位组合,得到相对总电子含量TEC;利用非掩星的辅助观测数据校正TEC,消除LEO卫星高度以上的TEC部分;在电子密度局部球对称假设和信号直线传播的近似下,通过Abel积分变换可以得到电子密度垂直廓线.将2007年度中与电离层测高仪站点经度差小于10°,纬度差小于2°的4903个COSMIC掩星电离层资料与相对应的电离层测高仪数据进行比较,F₂层的临界频率f₀F₂的标准差约为059 关键词： COSMIC GPS/LEO掩星 电离层测高仪 电离层反演     

基于卫星平台的全球大气一氧化碳柱浓度反演方法及结果分析

温室效应是全球气候变化的主要原因之一, 除温室气体外, 有毒气体一氧化碳(CO)作为一种非直接温室气体加剧了这种变化. 由于地基观测台站数量有限, 而大气化学模型的模拟又很大程度上依赖于模型假定, 因此, 卫星观测成为实时获取大气CO浓度分布信息的有效途径. Sciamachy是第一台搭载在卫星上, 利用观测到的近红外波段太阳反射光谱反演大气一氧化碳的仪器. 由于在近红外波段, 大气散射效应可以忽略, 所以Sciamachy观测数据能够很好地反演与人类活动息息相关的大气底层一氧化碳的时空变化信息. 本文基于迭代最大后验概率算法, 对Sciamachy的观测数据进行反演分析, 同时应用云效应校正与仪器本身问题校正方法, 得到了全球一氧化碳柱浓度时空分布结果; 通过与Atsr全球火点数据的比较, 分析了全球CO排放源的种类与时空分布; 最后选取中国地区CO柱浓度分布图, 并结合人口密度与煤田/煤矿分布, 对其排放源进行了初步推断.     

Experimental study of a plasma-filled backward wave oscillator

Experimental studies of a plasma-filled X-band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ⩽0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X-band Tm₀₁ mode prevailed when the background plasma density was below 6×10¹¹ cm^-3 . At a critical background plasma density of ≃8×10¹¹ cm^-3 power enhancement appeared in both X-band and the T-G modes. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse     

温稠密钛电导率计算

温稠密物质是惯性约束核聚变、重离子聚变、Z箍缩动作过程中物质发展和存在的重要阶段. 其热力学性质和辐射输运参数在聚变实验和内爆驱动力学模拟过程中有至关重要的作用. 本文通过建立非理想Saha方程, 结合线性混合规则的理论方法模拟了温稠密钛从10^-5-10 g·cm^-3, 10⁴ K到3×10⁴ K区间的粒子组分分布和电导率随温度密度的变化, 其中粒子组分分布由非理想Saha方程求解得到. 线性混合规则模型计算温稠密钛的电导率时考虑了包括电子、原子和离子之间的多种相互作用. 钛的电导率的计算结果与已有的爆炸丝实验数据相符. 通过电导率随温度密度变化趋势判断, 钛在整个温度区间, 密度0.56 g·cm^-3时发生非金属相到金属相相变. 对于简并系数和耦合系数的计算分析, 钛等离子体在整个温度和密度区间逐渐从弱耦合、非简并状态过渡到强耦合部分简并态.     

A two-component model for the electron distribution function in ahigh-current pseudospark or back-lighted thyratron

Temperature, energy, and densities of two electron distribution function components, including an isotropic bulk part and an anisotropic beam, are analyzed for a hydrogen pseudospark and/or back-lighted thyratron switch plasma with a peak electron density of 1-3×10¹⁵ cm^-3 and peak current density of ≈10⁴ A/cm². Estimates of a very small cathode-fall width during the conduction phase and high electric field strengths lead to the injection of an electron beam with energies ⩾100 eV and density of 10¹³-10¹⁴ cm^-3 into a Maxwellian bulk plasma. Collisional and radiative processes of monoenergetic beam electrons, bulk plasma electrons and ions, and atomic hydrogen are modeled by a set of rate equations, and line intensity ratios are compared with measurements. Under these high-current conditions, for an initial density n_H2=10¹⁶ cm^-3 and electron temperature of 0.8-1 eV, the estimated beam density is ≈10¹³ -10¹⁴ cm^-3. These results suggest the possibility of producing in a simple way a very high-density electron beam     

中纬度地区电离层偶发E层对量子卫星通信性能的影响

电离层偶发E层是指在距离地面高度80—150 km之间,在风剪切作用下,电子密度急剧增加的不规则电离薄层,它会对量子卫星光信号的传输造成极大的影响.然而,有关电离层偶发E层与星地间量子通信信道参数关系的研究,迄今尚未展开.为了研究偶发E层对量子卫星通信性能的影响,首先分析了它的形成过程,得出自由电子密度随高度变化的关系;然后建立了自由电子密度、偶发E层的厚度对量子卫星链路衰减的模型;针对振幅阻尼信道,给出自由电子密度对信道容量、纠缠保真度、误码率和安全密钥产生率的定量关系.理论分析和仿真结果表明,当偶发E层的厚度为1 km、电子密度由3×10~5cm~(-1)增加到27×10~5cm~(-1)时,信道容量由0.8304衰减到0.1319,纠缠保真度由0.9386下降到0.3606,量子误码率由0.0093增加到0.0769,安全密钥产生率由9.968×10~(-5)减小到1.91×10~(-6).由此可见,电子密度的大小和偶发E层的厚度对量子卫星通信性能有显著的影响.因此,在进行量子卫星通信时,应根据对电离层参数的探测情况,自适应调整卫星系统的各项指标,以确保量子通信的可靠性.     

A cold thermionically emitting dusty air plasma formed by radiativeheating of graphite particulates

Formation of an atmospheric pressure dusty air plasma is explored experimentally in this paper. The plasma is created by seeding an air flow with graphite particles and irradiating the particulates with a focused CO₂ laser beam. The graphite particles are, thus, heated to thermionically emitting temperatures, and average particle temperatures and average particle number densities are measured. The presence of charges is inferred both from these measured quantities using a simple theoretical transient model, and experimentally by applying a dc bias across the irradiated region. It is found that an electron density of ~6.7 × 10⁵ cm^-3 (6.7 × 10¹¹ m^-3) can be produced at steady state in the presence of O₂. This value can be increased to 3.6 × 10⁷ cm^-3 (3.6 × 10¹³ m ^-1) in the ideal case where an electron attachment to O₂ is suppressed and where a lower work function particulate is used     

Experimental study of CF4 conical theta pinch plasmaexpanding into vacuum

Langmuir probe, photodiode, and optical multichannel analyzer (OMA) measurements have been made on a pulsed CF₄ conical theta-pinch plasma. A cloud of CF₄ was puffed into a conical theta-pinch coil, converted to plasma, and propelled into the vacuum region ahead of the expanding gas cloud. At a position 67 cm away from the conical theta-pinch coil, the plasma arrived in separate packets that were about 20 μs in duration. The average drift velocity of these packets corresponded to an energy of about 3 eV. The OMA measurements showed that the second packet contained neutral atomic fluorine as well as charged particles. The electron temperature and ion density in the second packet were 2.0 eV and 1.5×10¹³ cm^-3, respectively. The electron temperature and ion density in the wake plasma were 8.3 eV and 4×10¹¹ cm^-3 , respectively. This device can be used for plasma processing or as a laboratory test of numerical and analytical models of the expansion of plasma into vacuum     

LaTiO高k栅介质Ge MOS电容电特性及Ti含量优化

采用共反应溅射法将Ti添加到La_2O_3中,制备了LaTiO/Ge金属-氧化物-半导体电容,并就Ti含量对器件电特性的影响进行了仔细研究.由于Ti-基氧化物具有极高的介电常数,LaTiO栅介质能够获得高k值;然而由于界面/近界面缺陷随着Ti含量的升高而增加,添加Ti使界面质量恶化,进而使栅极漏电流增大、器件可靠性降低.因此,为了在器件电特性之间实现协调,对Ti含量进行优化显得尤为重要.就所研究的Ti/La_2O_3比率而言,18.4%的Ti/La_2O_3比率最合适.该比率导致器件呈现出高k值(22.7)、低D_(it)(5.5×10~(11)eV~(-1)·cm~(-2))、可接受的J_g(V_g=1V,J_g=7.1×10~(-3)A·cm~(-2))和良好的器件可靠性.     

Ag纳米颗粒增强的Ho~(3+)/Tm~(3+)共掺铋锗酸盐玻璃的2μm发光研究

采用基于传统熔融淬冷技术的热化学还原法制备了系列Ag纳米颗粒复合Ho3+/Tm3+共掺铋锗酸盐玻璃样品,研究了Ag纳米颗粒含量对玻璃2μm发光特性的影响.结果表明,Ag纳米颗粒的表面等离子体共振带位于500—900 nm,峰值位于650 nm,透射电子显微镜图像中观察到均匀分布的Ag纳米颗粒,尺寸约为5—10 nm.通过测试玻璃样品在1.7—2.3μm波段的荧光光谱发现,Ag掺杂后Ho3+离子2μm处的荧光强度得到了极大的提高,其中AgCl掺杂质量分数为0.3%时的荧光强度比未掺杂时的荧光强度增强10倍,这归因于Ag纳米颗粒的局域场增强作用.计算得到Ho3+离子的吸收截面为0.491×10-20cm-2,发射截面为1.03×10-20cm-2,当增益系数为0.2时即可实现正的增益.     

The spatial and temporal development of pseudospark switch plasmas

Optical spectroscopy is used to investigate the spatial and temporal development of high-current pseudospark switch plasmas. At a peak discharge current of 12 kA in amplitude and a current reversal of 20%, the electron density is measured from Stark width broadening of the hydrogen Balmer beta line. The peak electron density of ~4×10¹⁵ cm^-3 is measured briefly after the current maximum. The discharge initially starts on the symmetry axis of the cathode hole. A cylindrical plasma column is observed, which is produced mainly by ionizing collisions of beam electrons formed in the hollow cathode during the early part of the discharge. This plasma column rapidly expands in the radial direction, until it contacts the edge of the cathode hole. The same behavior is found when the Balmer beta line intensity is evaluated rather than the line shape. Although statistically distributed, localized bursts of light are found occasionally, an axially symmetric, homogeneous light intensity distribution is always predominant, and the local arcing is merely superimposed on it. These results confirm that the discharge remains diffuse during most of the current pulse     

Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition

Pulsed metal organic chemical vapor deposition is introduced into the growth of In Ga N channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free In Ga N channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 × 1013cm-2is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cm2/V·s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that In Ga N channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional Ga N channel heterostructure. The gratifying results imply that In Ga N channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.