直流电弧等离子体炬数值模拟与诊断

直流电弧等离子体炬内部物理过程复杂且具动态性,较难对其进行准确描述与深入研究,且其工作温度较高,其状态参数难以使用常规方式测量。针对直流电弧等离子体炬,建立流动、传热和电磁相互耦合的数值模型,基于Fluent软件对直流电弧等离子体炬进行三维数值模拟和特性分析,设计并搭建了一套热焓探针实验系统,完成对直流电弧等离子体炬射流参数的测量分析。结果表明:建立的数值模型模拟结果与实验测量结果吻合较好,误差在10%以内;炬内温度与速度最大值与工作气流量呈正相关,均出现在靠近阴极区域,且沿轴线逐渐降低;等离子体炬内高温区与高电流密度区重合。     

Case study of inclined sporadic E layers in the Earth’s ionosphere observed by CHAMP/GPS radio occultations: Coupling between the tilted plasma layers and internal waves

We have used the radio occultation (RO) satellite data CHAMP/GPS (Challenging Minisatellite Payload/Global Positioning System) for studying the ionosphere of the Earth. A method for deriving the parameters of ionospheric structures is based upon an analysis of the RO signal variations in the phase path and intensity. This method allows one to estimate the spatial displacement of a plasma layer with respect to the ray perigee, and to determine the layer inclination and height correction values. In this paper, we focus on the case study of inclined sporadic E (E_s) layers in the high-latitude ionosphere based on available CHAMP RO data. Assuming that the internal gravity waves (IGWs) with the phase-fronts parallel to the ionization layer surfaces are responsible for the tilt angles of sporadic plasma layers, we have developed a new technique for determining the parameters of IGWs linked with the inclined E_s structures. A small-scale internal wave may be modulating initially horizontal E_s layer in height and causing a direction of the plasma density gradient to be rotated and aligned with that of the wave propagation vector k. The results of determination of the intrinsic wave frequency and period, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase speeds, and other characteristics of IGWs under study are presented and discussed.     

RPC-MAG The Fluxgate Magnetometer in the ROSETTA Plasma Consortium

The fluxgate magnetometer experiment onboard the ROSETTA spacecraft aims to measure the magnetic field in the interaction region of the solar wind plasma with comet 67P/Churyumov-Gerasimenko. It consists of a system of two ultra light (about 28 g each ) triaxial fluxgate magnetometer sensors, mounted on the 1.5 m long spacecraft boom. The measurement range of each sensor is ±16384 nT with quantization steps of 31 pT. The magnetometer sensors are operated with a time resolution of up to 0.05 s, corresponding to a bandwidth of 0–10 Hz. This performance of the RPC-MAG sensors allows detailed analyses of magnetic field variations in the cometary environment. RPC-MAG furthermore is designed to study possible remnant magnetic fields of the nucleus, measurements which will be done in close cooperation with the ROSETTA lander magnetometer experiment ROMAP.     

Relationship Between Substorm Auroras and Processes in the Near-Earth Magnetotail

Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase shows that these parameters have the comparable values. This is a clear evidence of the loading–unloading scheme of substorm development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for monitoring of substorm intensity in terms of the magnetic flux and energy dissipation.     

感性耦合夹层等离子体隐身天线罩电磁散射分析

设计了一种石英夹层感性耦合等离子体（ICP）隐身天线罩模型,采用有限元与Z变换时域有限差分（ZT-FDTD）联合仿真的方法,建立了ICP放电的流体模型,得到不同气压及功率下与电磁散射相关的电子密度空间分布,在此基础上建立Z变换时域有限差分法模型,对石英夹层等离子体隐身天线罩的宽频段后向散射进行计算,同时利用微波干涉法及XFDTD软件对算法及程序进行验证。结果表明：感性耦合等离子体可产生较高密度等离子体,能有效实现雷达散射截面（RCS）的减缩,在气压为2 Pa时,碰撞衰减较弱,等离子体密度分布较均匀,衰减带宽集中在等离子体振荡频率附近,功率增加会使衰减峰值向高频方向移动,气压为20 Pa时,碰撞衰减增强,且等离子体密度分布有较大梯度,衰减带宽有效增加,同时RCS曲线的波动特性加强。     

Universal scaling laws for fully-developed magnetic field turbulence near and far upstream of the Earth’s bow shock

We analyze the multifractal scaling of the modulus of the interplanetary magnetic field near and far upstream of the Earth’s bow shock, measured by Cluster and ACE, respectively, from 1 to 3 February 2002. The maximum order of the structure function is carefully estimated for each time series using two different techniques, to ensure the validity of our high-order statistics. The first technique consists of plotting the integrand of the pth order structure function, and the second technique is a quantitative method which relies on the power-law scaling of the extreme events. We compare the scaling exponents computed from the structure functions of magnetic field differences with the predictions obtained by the She–Lévêque model of intermittency in anisotropic magnetohydrodynamic turbulence. Our results show a good agreement between the model and the observations near and far upstream of the Earth’s bow shock, rendering support for the modelling of universal scaling laws based on the Kolmogorov phenomenology in the presence of sheet-like dissipative structures.     

Total electron content of the ionosphere at two stations in East Africa during the 24–25 October 2011 geomagnetic storm

The equatorial ionosphere has been known to become highly disturbed and thus rendering space-based navigation unreliable during space weather events, such as geomagnetic storms. Modern navigation systems, such as the Global Positioning System (GPS) use radio-wave signals that reflect from or propagate through the ionosphere as a means of determining range or distance. Such systems are vulnerable to effects caused by geomagnetic storms, and their performance can be severely degraded. This paper analyses total electron content (TEC) and the corresponding GPS scintillations using two GPS SCINDA receivers located at Makerere University, Uganda (Lat: 0.3^o N; Lon: 32.5^o E) and at the University of Nairobi, Kenya (Lat: 1.3^o S; Lon: 36.8^o E), both in East Africa. The analysis shows that the scintillations actually correspond to plasma bubbles. The occurrence of plasma bubbles at one station was correlated with those at the other station by using observations from the same satellite. It was noted that some bubbles develop at one station and presumably “die off” before reaching the other station. The paper also discusses the effects of the geomagnetic storm of the 24–25 October 2011 on the ionospheric TEC at the two East African stations. Reductions in the diurnal TEC at the two stations during the period of the storm were observed and the TEC depletions observed during that period showed much deeper depletions than on the non-storm days. The effects during the storm have been attributed to the uplift of the ionospheric plasma, which was then transported away from this region by diffusion along magnetic field lines.     

日球层内外能量中性原子的探测

能量中性原子(Energetic Neutral Atoms, ENA, 简称能原子)是指在日球层内外空间, 拥有>0.1keV动能的原子.在此空间领域并没有温度>106K的中性气体, 但却充满动能>0.1keV的正离子.因此能原子A应该是A+离子与原地稀薄气体B原子或分子交换电荷所产生的, 即A++B→A+B+. 电荷交换涉及极小的动能变化, 新生的能原子A和离子B+基本上各自保持原有动能. 离子B+随即被当地磁场俘获, 能原子A则脱离磁场约束并携带其原属离子群的成分和能量信息而直线运动, 成为遥测空间等离子体的有效媒介. 美国人造卫星 IBEX (Interstellar Boundary Explorer) 直接探测得到来自日球层以外星际空间的能原子, 大幅延伸了利用能原子遥测空间等离子体的领域. 本文据此论述了空间能原子的发现, 综述了探测空间能原子的基本概念与实例、取得的主要成果、仪器设计和研制进展以及未来空间利用能原子遥测的发展趋势.      

Spectroscopic data and Stark broadening of Cu I and Ag I spectral lines: Selection and analysis

Optical emission and linear laser absorption spectroscopy techniques were used in investigation of plasma with copper and silver admixture. The method of selection of spectral lines and spectroscopic data with the aim of diagnostics of multicomponent air plasma with two metal vapors admixture was developed. Energy level populations behavior on the Boltzmann plot were used for Cu I and Ag I spectroscopic data selection. In this way the selection of spectroscopic data for some of Cu I and Ag I lines was realized. Stark broadening parameters of Cu I and Ag I were examined. Experimentally obtained temperature and electron density radial distributions were used in the calculation of plasma composition in the assumption of local thermodynamic equilibrium. Linear laser absorption spectroscopy was used to examine the state of plasma.     

Spectroscopy peculiarities of thermal plasma of electric arc discharge between electrodes with Zn admixtures

Plasma of the free burning electric arc between Ag–SnO₂–ZnO composite electrodes as well as brass electrodes were investigated. The plasma temperature distributions were obtained by Boltzmann plot method involving Cu I, Ag I or Zn I spectral line emissions. The electron density distributions were obtained from the width and from absolute intensity of spectral lines. The laser absorption spectroscopy was used for measurement of copper atom concentration in plasma. Plasma equilibrium composition was calculated using two independent groups of experimental values (temperature and copper atom concentration, temperature and electron density). It was found that plasma of the free burning electric arc between brass electrodes is in local thermodynamical equilibrium. The experimental verification of the spectroscopic data of Zn I spectral lines was carried out.