Growth mechanism and characteristics of electron drift instability in Hall thruster with different propellant types

The existence of a significant electron drift instability(EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In recent years, extensive simulation research on the characteristics of EDI has been conducted, but the excitation mechanism and growth mechanism of EDI in linear stage and nonlinear stage remain unclear. In this work, a one-dimensional PIC model in the azimuthal direction of the thruster near-exit region is established to gain further insights into the mechanism of the EDI in detail, and the effects of different types of propellants on EDI characteristics are discussed. The changes in axial electron transport caused by EDI under different types of propellants and electromagnetic field strengths are also examined. The results indicate that EDI undergoes a short linear growth phase before transitioning to the nonlinear phase and finally reaching saturation through the ion Landau damping. The EDI drives a significant ion heating in the azimuthal direction through electron–ion friction before entering the quasi-steady state, which increases the axial mobility of the electrons. Using lighter atomic weight propellant can effectively suppress the oscillation amplitude of EDI, but it will increase the linear growth rate, frequency, and phase velocity of EDI. Compared with the classical mobility, the axial electron mobility under the EDI increases by three orders of magnitude, which is consistent with experimental phenomena. The change of propellant type is insufficient to significantly change the axial electron mobility. It is also found that the collisions between electrons and neutral gasescan significantly affect the axial electron mobility under the influence of EDI, and lead the strength of the electric field to increase and the strength of the magnetic field to decrease, thereby both effectively suppressing the axial transport of electrons.

The effective ionization coefficients and electron drift velocities in gas mixtures of CF_3I with N_2 and CO_2 obtained from Boltzmann equation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients（α-η）/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend（SST） experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td（1 Td = 10-17V·cm2）,while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of（αη）/N with the CF3I mixture ratio k,the limiting field strength（E/N） lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of（E/N） lim are essentially the same as that for pure SF 6.Additionally,the global warming potential（GWP） and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by E ×B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investi- gated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the con- ventionM theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.

An experimental research on the instability of ion acoustic wave with electron drift

As electron temperature Te is much higher than ion temperature Ti, and electron driftspeed Vd is larger than the critical value Vdc of Vd, the ω=KVφ mode ion acoustic wave（IAW） will be instable. Under a long wave condition （KλD【【1, where λD is Deby length,K is weve number）, the growing rate γ（K） of the IAW may be written

Readout electronics for a high-resolution soft X-ray spectrometer based on silicon drift detector

The readout electronics for a prototype soft X-ray spectrometer based on silicon drift detector(SDD),for precisely measuring the energy and arrival time of X-ray photons is presented in this paper.The system mainly consists of two parts,i.e.,an analog electronics section(including a pre-amplifier,a signal shaper and filter,a constant fraction timing circuit,and a peak hold circuit)and a digital electronics section(including an ADC and a TDC).Test results with X-ray sources show that an energy dynamic range of 1-10 keV with an integral nonlinearity of less than 0.1%can be achieved,and the energy resolution is better than 160 eV @ 5.9 keV FWHM.Using a waveform generator,test results also indicate that time resolution of the electronics system is about 3.7 ns,which is much less than the transit time spread of SDD(<100 ns)and satisfies the requirements of future applications.

Corotating drift-bounce resonance of plasmaspheric electron with poloidal ULF waves

The purpose of this paper is to understand how low energy plasmaspheric electrons respond to ULF waves excited by interplanetary shocks impinging on magnetosphere. It is found that both energy and pitch angle dispersed plasmaspheric electrons with energy of a few eV to tens of eV can be generated simultaneously by the interplanetary shock. The subsequent period of successive dispersion signatures is around 40 s and is consistent with the ULF wave period(third harmonic). By tracing back the energy and pitch angle dispersion signatures, the position of the electron injection region is found to be off-equator at around -32° in the southern hemisphere. This can be explained as the result of injected electrons being accelerated by higher harmonic ULF waves(e.g. third harmonic) which carry a larger amplitude electric field off-equator. The dispersion signatures are due to the flux modulations(or accelerations) of " local" plasmaspheric electrons rather than electrons from the ionosphere. With the observed wave-borne large electric field excited by the interplanetary shock impact, the kinetic energy can increase to a maximum of 23 percent in one bouncing cycle for plasmaspheric electrons satisfying the drift-bounce resonance condition by taking account of both the corotating drift and bounce motion of the local plasmaspheric electron.

Observations of mode frequency increase and the appearance of ITB during the m/n=1/1 kink mode in EAST high electron temperature long pulse operation

A new long-pulse high electron temperature(Te)regime has been achieved on experimental advanced superconducting tokamak by pure radio frequency heating.In this new scenario,there are mainly two confinement states involving two magneto-hydrodynamic(MHD)modes,one of which is identified as m/n=1/1 kink mode(where m and n are the poloidal and toroidal mode numbers,respectively).The frequency evolution of the kink mode is investigated through the three-dimensional,toroidal,and nonlinear Hall-MHD code CLT.We firstly find that the frequency of the m/n=1/1 kink mode significantly increases during each sawtooth crash and then confirmed it through the experimental data.The simulation results indicate that the increase of the mode frequency is mainly due to the significant increase of the electron diamagnetic frequency nearby the reconnection region.We have also observed the internal transport barrier(ITB)during the m/n=1/1 kink mode.To further investigate this m/n=1/1 kink mode in this new regime,the multi-scale interactions between the m/n=1/1 kink mode and turbulence are discussed.

Development of Electron Temperature Measuring System by Silicon Drift Detector

The soft X-ray spectroscopy, laser Thomson scattering and electron cyclotron emission （ ECE ） are usually adopted for electron temperature measurement in fusion research of magnetic confinement. The particular soft X-ray spectroscopy has the very good spatial-temporal resolution and smaller measuring error than laser Thomson scattering, a close spatial-temporal resolution to ECE, absolute measurement ability, and smaller influence by suprathermal and runaway electrons than ECE.

金属卤素钙钛矿CsPbBr3的电声耦合输运特性研究

金属卤素钙钛矿CsPbBr_(3)在发光方面(Light emitter)的优良表现吸引了许多人把它作为下一代发光、显示与量子信息的可选材料,但其关键的漂移迁移率会受到声子限制.本文将以第一性原理计算得到CsPbBr_(3)的包括极性光学声子(Polar optical phonon)在内的电声耦合特性,然后使用线性玻尔兹曼方程给出在电场下的解,从而得出漂移迁移率.在论文详述中会给出CsPbBr_(3)的各向异性载流子输运特性的研究,为金属卤素钙钛矿的应用提供一些必要信息.

Electron Spin and Proton Spin in the Hydrogen and Hydrogen-Like Atomic Systems

The mechanical angular momentum and magnetic moment of the electron and proton spin have been calculated semiclassically with the aid of the uncertainty principle for energy and time. The spin effects of both kinds of the elementary particles can be expressed in terms of similar formulae. The quantization of the spin motion has been done on the basis of the old quantum theory. It gives a quantum number n = 1/2 as the index of the spin state acceptable for both the electron and proton particle. In effect of the spin existence the electron motion in the hydrogen atom can be represented as a drift motion accomplished in a combined electric and magnetic field. More than 18,000 spin oscillations accompany one drift circulation performed along the lowest orbit of the Bohr atom. The semiclassical theory developed in the paper has been applied to calculate the doublet separation of the experimentally well-examined D line entering the spectrum of the sodium atom. This separation is found to be much similar to that obtained according to the relativistic old quantum theory.

华龙一号应急柴油发电机组机械调速器漂移故障分析及解决方案

调速器作为柴油发电机组转速控制的核心部件,对核电厂应急柴油发电机组的安全运行以及全厂失电后恢复应急供电都起着至关重要的作用。结合电子调速器和机械调速器的特点,对华龙一号某核电厂应急柴油发电机组出现的机械调速器零点漂移问题,从调速系统配置、切换逻辑、定值设置、漂移事件过程及后果进行全方面的分析。按照不影响应急柴油发电机组并网以及电子调速器执行安全功能实现的原则,从优化机调定值设置、改善设备运行环境以及增加Droop模式等角度提供解决方案。

Manifestations of the earthquake preparations in the ionosphere total electron content variations

Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seismic events during 2005-2006. The F2-layer ionospheric plasma drift under action of the electric fields of seismic origin is proposed as the main reason of producing TEC anomalies. The origin of such electric fields is discussed in terms of the lithosphere-atmosphere-ionosphere coupling system. This theory is supported by numerical simulations using global Upper Atmosphere Model (UAM). UAM calculations show that the vertical electric current with the density of about 20 - 40 nA/m2 flowing between the Earth and ionosphere over an area of about 200 by 2000 km is required to produce the TEC disturbances with the amplitude of about 30% - 50% relatively to the non-disturbed conditions. Ionosphere responses on the variations of the latitudinal position, direction and configuration of the vertical electric currents have been investigated. We show that not only the vertical component of the ionospheric plasma drift but also horizontal components play an important role in producing pre-earthquake TEC disturbances.

基于图像分割和盲反卷积的透射电镜图像漂移校正方法

样品漂移是影响透射电子显微镜分辨率的重要因素之一。近年来有一系列关于透射电镜图像漂移校正的算法,如Unblur、MotionCor和MotionCor2等,在冷冻电镜三维重构方面应用效果显著,但无法应用于材料表征电镜通常配备的CCD相机的图像漂移校正。本文提出了一种基于图像分割和盲反卷积的透射电镜图像漂移校正方法,在Goldstein和Fattal提出的利用功率谱的统计不规则性估计卷积核算法的基础上,利用图像分割解决了电镜图像样品部分和背景部分的运动方式不一致问题,能够应用于CCD相机的图像漂移校正。实验结果表明,本文的方法能够有效提高电镜图像的分辨率。

模拟式电子汽车衡出现漂移现象的检测研究

汽车衡作为一种便于称量载货汽车重量的工具,因其使用携带方便、快速、准确,而出现在许多高速收费站、海港口、矿山、企业、运输、贸易等行业中。针对模拟式电子汽车衡易出现漂移现象的问题,介绍了运用数字式汽车衡仪表对模拟式电子汽车衡漂移现象进行快速检测的具体方法与步骤,以供模拟式电子汽车衡漂移现象的检测参考。

空间电磁卫星的粒子探测与汶川地震

通过电磁卫星研究地震与空间电离层和磁层的电磁场等参数的变化关系作为地面地震预报研究的补充,是近年来研究地震规律和预报方式的一个新的研究方向,研究空间带电粒子的相关特性是其中的一个重要内容.分析了法国DEMETER电磁卫星上的高能电子探测器在2008年间的探测数据,特别是在我国汶川地震前后的数据,研究了内辐射带高能电子在东西经度方向漂移的情况;地震前后汶川上空及不同经纬区域范围内空间电子能谱的变化;以及汶川地区的余震与空间电子通量在短时标上的关联.发现在90～600 keV能区,90°E～110°E,47°N～49°N的汶川北部区域,地震当天与地震前后几天的能谱有明显差别;在VLF发射站引起的电子沉降带上的能谱在地震前有显著低能段涨高.

星载电场仪的电场测量方法

空间电场是研究空间天气学和空间环境的一个重要参量,它与空间磁场监测相辅相成。本文详细评述了国外星载电场仪的电场测量方法。首先简述了空间电场测量在空间天气学应用研究方面的重要性和发展状况及趋势;针对国外不同卫星搭载的电场仪,讨论了空间电场的两种主要测量方法——双探针电场测量法和电子漂移电场测量法,指出了其工作原理、特点、使用范围和局限性;最后,对比这两种测量方法,并展望了星载电场仪的使用前景,这些对中国刚刚起步的星载电场仪研究是非常重要的。

电子鼻鉴别白酒信号小波去漂移方法

为提高电子鼻长期鉴别的稳健性,提出了一种基于小波分析的电子鼻信号去漂移方法。对含漂移信号的电子鼻数据进行小波分解,获得分解系数;构造一种相对偏差阈值滤波函数对小波逼近系数进行阈值处理,获得修正的小波系数;运用小波逆变换对修正后的小波系数进行重构,得到去除漂移或少漂移的电子鼻信号。对6种白酒样本随机生成的5组样本训练集与对应的测试集进行去漂移处理与信号重构,提取去漂移处理前后的电子鼻信号积分值特征,并运用Fisher判别分析(FDA)和BP神经网络分别对5组数据集进行鉴别分析。FDA鉴别结果显示,无论是训练集还是测试集,5组样本的鉴别正确率由去漂移前的最高值45%提升至去漂移后的100%。BP神经网络鉴别结果显示,5组样本的鉴别正确率由去漂移前的最高值31.7%提升至去漂移后的98.3%。这说明所给出的去漂移方法在白酒电子鼻的鉴别中是稳健有效的。同时,也为电子鼻鉴别其他物品提供了一种可借鉴的去漂移方法。

在He/C_3H_8(60/40)混合气体中电子的漂移和倍增

报道用均匀场漂移室测量得到在He/C3H8(60/40)混合气体中的电子饱和漂移速度为3.8cm/μs。气体增益在2×104以上将出现饱和效应。由于很好地降低了放大器的噪音干扰,在55Fe能谱的低端观察到1.5keVAl的特征KX射线在He原子上产生的的全能光电峰。

独立分量分析融合小波能量阈值的电子鼻信号去漂移方法

电子鼻在长期使用过程中,由于受到传感器老化和温湿度波动等因素的影响,使得电子鼻信号存在着漂移现象,制约了电子鼻的准确检测。为了提高电子鼻鉴别多组分复杂食品时的长期稳健性,提出了一种独立分量分析(independent component analysis,ICA)融合小波能量阈值的去漂移信号方法。首先,运用ICA分解电子鼻信号以获得各个独立成分;其次,根据各个独立成分的小波能量值选择独立成分,以剔除漂移信号;最后,运用所选择的独立成分重构电子鼻信号。选用6种白酒样品和6种食醋样品进行电子鼻鉴别验证:在分别提取2类样品去漂移前后的电子鼻信号积分值(integral value,INV)特征后,分别对6种白酒样品和6种食醋样品进行了Fisher判别分析(fisher discriminant analysis,FDA),FDA的鉴别正确率分别由去漂移前的34.3%(白酒样品)、75.7%(食醋样品)提升到去漂移后的100%(白酒样品)、99.7%(食醋样品)。Fisher判别分析结果表明,所提出的电子鼻信号去漂移方法是有效的。与其他独立分量分析方法相比,该方法不受先验信息的影响,更便于实际应用,研究结果不仅适用于白酒、食醋样品的鉴别,也为其他类型的样品鉴别提供参考。

圆柱形阳极层霍尔推力器内轮辐效应的实验研究

为了研究圆柱形阳极层霍尔推力器内关于电子反常输运的轮辐效应(Rotating Spoke),分别采用高速相机和静电探针来捕捉圆柱形阳极层霍尔推力器内的轮辐效应图像和等离子体震荡频率。结果表明:在放电电压350V,放电电流3.5A,阳极上表面处的磁场强度为125Gs,工作气压为2×10-2Pa时,由测得轮辐效应的放电图像和波形可知,轮辐效应的频率为10kHz^12.5kHz。当磁场强度增加到205Gs,放电电流增加到4A时,轮辐效应的频率增加到25kHz,并且轮辐效应出现分裂和合并现象。此研究结果表明,圆柱形阳极层霍尔推力器内不仅存在轮辐效应现象以及角向电场,而且不同的工作参数会有不同的轮辐效应模式和频率。