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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. 相似文献
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黄林 《核聚变与等离子体物理》1987,(1)
本文研究了离子束-等离子体系统的电磁不稳定性,考虑了离子-电子和离子-离子碰撞对维泊耳(Weibel)型电磁不稳定性增长率的影响。结果表明,在离子束-等离子体系统中可以激发维泊耳型电磁不稳定性,离子和电子之间的碰撞将使这类不稳定性的增长率增加。 相似文献
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在Chen等理论模型的基础上,对损失锥-束流分布电子激发的回旋激射不稳定性的主要特征 进行了深入研究,这种电子分布在太阳色球附近的磁重联过程中可能形成,它兼有束流和损 失锥的特性.结果表明,它不仅可以像束流分布和损失锥分布那样在适当的等离子体频率和 回旋频率的比值范围内激发X模和O模的基频和谐频不稳定性,兼有两种分布的激发特性,而 且具有更强的增长率.这一方面丰富了此类等离子体不稳定性的基本内容,而且预期在天体 射电发射机理的研究中也将得到广泛的应用.
关键词:
回旋激射不稳定性
弱相对论性
损失锥-束流分布电子
增长率 相似文献
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利用理想磁流体力学(MHD)模型对有轴向流参与的Z箍缩等离子体不稳定性进行了分析.对可压缩平板等离子体模型的色散关系进行了推导,讨论了三种不同等离子体状态下的不稳定性增长率.结果显示,等离子体的可压缩性对磁瑞利-泰勒/开尔文-亥姆霍兹(MRT/KH)杂化不稳定性有抑制作用,改善了轴向剪切流对长波长扰动的影响.分析了不同轴向流速度分布对系统稳定性的影响.结果表明,对于峰值相同的不同轴向流,其对不稳定性的抑制效果只依赖于扰动集中区域内速度剪切的大小,与其他位置的速度剪切无关.
关键词:
Z箍缩
磁瑞利-泰勒不稳定性
轴向剪切流
MHD方程 相似文献
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Bunch lengthening phenomenon is resulted from one of the most severe single bunch instabilities in storage rings. We develop a new code to calculate the single bunch length and energy spread in storage rings using FORTRAN. In this code, wake field is calculated using an analytical formula, which is different from the previous ones. The bunch length and energy spread under different bunch currents are calculated for BEPCII by using this code, and the tracking results are in good agreement with those from other codes. The calculated energy spread clearly shows that the longitudinal microwave instability threshold is around 65 mA for BEPCII storage ring. 相似文献
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Electron cloud instability (ECI) may take place in a storage ring when the machine is operated with multi-bunch positively charged beam. According to the actual shape of vacuum chamber in BEPCⅡ, a computer simulation program has been developed. With the code, the electron density in the chamber with the different widths of antechamber and the different secondary electron yields, respectively, can be obtained. The possibility to put clearing electrodes in the normal chamber or ante-chamber to reduce the electron density in the central region of the chamber is also investigated. In the simulation, the coherent oscillation of bunches and the formation of electron cloud (EC) are tracked simultaneously. The sideband distribution and growth rate can be obtained through tracking and dealing the bunch oscillation amplitude with FFT. Based on the head-tail model, the single bunch instability induced by EC is also studied. By the simulation, for BEPCⅡ the threshold density for the single bunch instability is estimated to be~10 12 m -3 and the restraining measures that might be adopted in BEPCⅡ can control the EC density under the threshold. According to the simulation results, a relatively big positive chromaticity should be used to suppress the bunch blow up. 相似文献
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When a heteroepitaxial film is grown on a vicinal substrate, the terrace steps at the growth front may bunch together to relieve strain, resulting in a rough surface. On the other hand, proper manipulation of the growth kinetics may suppress the inherent bunching instability, thus preserving step-flow growth. Here we show that the step dynamics in the early stages of growth can already determine whether the bunching instability is truly suppressed, prior to bunching actually taking place in the unstable regime. We determine the critical film thickness above which steps will bunch and exploit its scaling properties and usefulness for extracting intrinsic energy parameters. Experimental studies of SrRuO(3) films grown on vicinal SrTiO(3) substrates clearly establish the existence of the critical film thickness in step bunching. 相似文献
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Byrd JM Hao Z Martin MC Robin DS Sannibale F Schoenlein RW Zholents AA Zolotorev MS 《Physical review letters》2006,97(7):074802
We report the first observation of laser seeding of the storage-ring microbunching instability. Above a threshold bunch current, the interaction of the beam and its radiation results in a coherent instability, observed as a series of stochastic bursts of coherent synchrotron radiation (CSR) at terahertz frequencies initiated by fluctuations in the beam density. We have observed that this effect can be seeded by imprinting an initial density modulation on the beam by means of laser "slicing." In such a situation, most of the bursts of CSR become synchronous with the pulses of the modulating laser and their average intensity scales exponentially with the current per bunch. We present detailed experimental observations of the seeding effect and a model of the phenomenon. This seeding mechanism also creates potential applications as a high-power source of CSR at terahertz frequencies. 相似文献
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A theory is presented of cyclotron superradiance from an electron bunch rotating in a uniform magnetic field and drifting at a velocity close to the group velocity of a wave propagating in a waveguide. It is shown that, in a comoving frame of reference, the bunch emits radiation at a frequency close to the cutoff frequency of the waveguide. Superradiance implies the azimuthal self-bunching of electrons, which is accompanied by coherent emission of the stored rotational energy in a short electromagnetic pulse. Linear and nonlinear stages of the process are analyzed. The growth rate of the superradiance instability is determined. It is shown that the maximum growth rate is attained under group synchronism conditions. The peak power and the characteristic duration of the cyclotron superradiance pulse are determined by numerical simulation. The characteristic features of the superradiance pulses are described in the comoving and laboratory frames. The results of theoretical analysis are compared with experimental data. 相似文献