Responses of properties in the plasma sheet and at the geosynchronous orbit to interplanetary shock

On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front （i.e., southward turning）. When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times （MLTs） all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.     

Convective high-speed flow and field-aligned high-speed flows explored by TC-1

From June 1, 2004 to October 31, 2006, a total 465 high-speed flow events are observed by the TC-1 satellite in the near-Earth region （-13 RE〈X〈-9 RE, ｜Y｜〈10 RE, ｜Z＋〈5 RE）, Based on the angle between the flow and the magnetic field, the high-speed flow events are further divided into two types, that is, field-aligned high-speed flow （FAHF） in the plasma sheet boundary and convective bursty bulk flow （BBF） in the center plasma sheet, Among the total 465 high-speed flow events, there are 371 FAHFs, and 94 BBFs, The CHF are mainly concentrated in the plasma sheet, the intersection angle between the flow and the magnetic field is larger, the magnetic field intensity is relatively weak, The FHF are mainly distributed near the boundary layer of the plasma sheet, the intersection angle between the flow and magnetic field is smaller, and the magnetic field intensity is relatively strong, The convective BBFs have an important effect on the substorm,     

Plasma sheet stretching accompanied by field aligned energetic ion fluxes observed by the NUADU instrument aboard TC-2

The NUADU (NeUtral Atom Detector Unit) instrument aboard TC-2 recorded 4л solid angle images of charged particles (E >180 keV) spiraling around the magnetic field lines in the near-Earth plasma sheet (at ~ -7 RE, equatorial dawn-to-night side) during a geomagnetic storm (Dst =-219 nT) on August 24, 2005. Energetic ion beam events characterized by symmetrical, ring-like, solid angle distributions around ambient magnetic field lines were observed during a 34-minute traversal of the plasma sheet by the TC-2 spacecraft. Also, observations during these multiple crossings of the plasma sheet were monitored by the magnetometer experiment (FGM) aboard the same spacecraft. During each crossing, a whistler-mode chorus enhancement was observed in the anisotropic area by the TC-2 low frequency electromagnetic wave detector (LFEW/TC-2) at a frequency just above that of the local lower hybrid wave. A comparison of the ion pitch angle distribution (PAD) map with the ambient magnetic field shows that an enhancement in the field aligned energetic ion flux was accompanied by tailward stretching of the magnetic field lines in the plasma sheet. In contrast, the perpendicular ion-flux enhancement was accompanied by a signature indicating the corresponding shrinkage of the magnetic field lines in the plasma sheet. Since both parallel ion-flux and perpendicular ion-flux enhancements occurred intermittently, the data were interpreted to imply a dynamical, oscillatory process of the magnetic field line (stretching and shrinking) in the near-Earth plasma sheet, which might have acted to help establish an interaction region in this area which would support continuous aurora-substorm triggering during the ongoing magnetic storm. The whistler-mode chorus may have been produced due to ion gyro-resonance during particle pitch angle diffusion after the plasma sheet compression.     

Comparison between magnetic coplanarity and MVA methods in determining the normal of Venusian bow shock

With the measurements of magnetic field of Venus Express (VEX), magnetic coplanarity and minimum variance analysis (MVA) methods are analyzed and their validity is tested to determine the normal of Venusian bow shocks. It is found that MVA method is the better than magnetic coplanarity, and 95% shock crossings can be accurately determined by the method. However, the occurrence of the shock normal which is not determined accurately by magnetic coplanarity increases with the decrease of the solar zenith angle (SZA). At the same time, compared with quasi-parallel shocks, there is more occurrence of the shock normal which cannot be determined accurately by magnetic coplanarity for quasi-perpendicular shocks.     

Observations of kinetic Alfvén waves by THEMIS near a substorm onset

Low frequency electromagnetic fluctuations in the vicinity of a magnetospheric substorm onset were investigated using simultaneous observations by THEMIS multiple probes in the near-Earth plasma sheet in the magnetotail.The observations indicate that in the vicinity of a substorm onset,kinetic Alfvén waves can be excited in the high-βplasma sheet(β=2μ0nT/B 2 ,the ratio of plasma thermal pressure to magnetic pressure)within the near-Earth magnetotail.The kinetic Alfvén wave has a small spatial scale in the high-βplasma.The parallel electric field accompanying kinetic Alfvén waves accelerates the charged particles along the magnetic field.The kinetic Alfvén waves play an important role in the substorm trigger process,and possibly in the formation of a substorm current wedge.     

1Cr18Ni9Ti不锈钢薄板等离子电弧加热弯曲成形的温度场

为获得等离子电弧加热工艺参数和薄板几何尺寸对薄板温度场分布的影响规律,应用有限元方法对1Cr18Ni9Ti不锈钢薄板等离子电弧加热弯曲成形的三维瞬态温度场进行了数值模拟,分析了等离子电弧功率、扫描速度、薄板厚度以及冷却条件等对等离子电弧成形温度场的影响特性.结果表明:1Cr18Ni9Ti不锈钢薄板的弯曲角度随着等离子电弧功率的增加而增加,最佳扫描速度下薄板厚度方向温度梯度达到最大.改变温度梯度可以达到控制变形的目的.     

Auroral substorm response to solar wind pressure shock

Two cases of auroral substorms have been studied with the Polar UVI data, which were associated with solar wind pressure shock arriving at the Earth. The global aurora activities started about 1–2 min after pressure shocks arrived at dayside magnetopause, then nightside auroras intensified rapidly 3–4 min later, with auroral substorm onset. The observations in synchronous orbit indicated that the compressing effects on magnetosphere were observed in their corresponding sites about 2 min after the pressure shocks impulse magnetopause. We propose that the auroral intensification and substorm onset possibly result from hydromagnetic wave produced by the pressure shock. The fast-mode wave propagates across the magnetotail lobes with higher local Alfven velocity, magnetotail was compressed rapidly and strong lobe field and cross-tail current were built in about 1–2 min, and furthermore the substorm was triggered due to an instability in current sheet.     

流动重力模不稳定性

本文研究了在垂直于磁场和等离子体流动的重力场中具有剪切流动的电流片的稳定性。这种由剪切流动和重力联合作用所引起的混合模,称为流动重力模不稳定性。作为一个例子,还讨论了弱重力场情况下激发流动重力模不稳定性的临界条件。     

磁层亚暴过程中高速流分布

采用实际的磁尾位型,利用数值模拟方法研究磁层亚暴过程中高速流分布。结果表明垂直磁场的高速流主要分布在电流片内,范围在|Z|<0.25RE;平行磁场高速流分布区域在两个区域较大,一个是距离地球较近的磁场较强的区域,另一个是距离等离子体片较近磁场较强的区域。     

等离子体气动激励控制圆锥激波实验

以减弱超声速飞机头部和进气道调节锥的激波强度为背景,开展了等离子体气动激励控制圆锥激波实验,通过纹影显示以及壁面压力测量来研究圆锥激波形态和激波强度变化的规律。结果表明:当激励电压幅值分别为600V,800V,1 000V时,等离子体气动激励使圆锥激波变为2道激波,激波角度分别增大7.3°、13.2°、18.9°,锥体头部壁面总压分别增大6.52%、8.17%、9.52%,表征总压损失减小,验证了等离子体气动激励可以有效减弱超声速飞机头部和进气道调节锥圆锥激波强度。     

两种螺旋波天线对非均匀等离子体波场结构的影响

基于气体工质电离后被射频加热的稳态过程,在石英管中等离子体沿径向不均匀分布条件下,研究分析了1Loop型和Boswell型等2种螺旋波天线激发出的射频波功率对波场结构的影响情况。运用Helic程序求解管内电磁场相关的4个径向微分方程,得到波电场和波磁场的分布情况。通过分析两型天线对螺旋波等离子体波场结构的影响,对比2种天线的性能。结果发现:L型天线激发的波场属于强静电弱磁波场,B型天线激发波场则属于强静电强磁波场;B型天线相比L型天线能够在天线覆盖范围内产生强波电场,该天线下更多功率耦合进了等离子体中。L天线激发波电场受密度梯度影响显著,L天线对靠近壁面处等离子体影响范围大于B天线,B型天线激发波场能量更强。     

激波法向和速度的确定

本文列举了各种计算行星际激波方向的方法，讨论了各种计算方法的适用范围。利用激波跳跃条件，得到激波法向磁场与激波两侧介质参量的关系。这样，从行星际激波的观测数据，可以求出激波的法向磁场，判断该激波是平行激波，垂直激波或斜激波。对不同类型的激波，挑选不同的计算方法，使它合适于不同类型的跃变关系特点，从而得到正确的计算结果。最后给出三个计算激波方向的例子。     

MPCVD 法工艺特性对 SnO_2 薄膜导电性的影响

研究了磁等离子体化学气相沉积的不同工艺条件对ＳｎＯ２薄膜导电性的影响．实验结果表明,外加适当位形、大小的纵向磁镜场,可使等离子体化学气相沉积技术中制备ＳｎＯ２薄膜所需的氧气流量降低,沉积时间缩短,且制得的薄膜电阻大大降低,轴向分布均匀性明显增强．对以上结果进行了分析和讨论．     

An asymmetric solar wind termination shock

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, approximately 10 au closer to the Sun than found by Voyager 1 in the north. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field, from transient-induced shock motion, or from the solar wind dynamic pressure. Here we report that the intensity of 4-5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma, magnetic field, plasma-wave and lower energy particle observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock or in the heliosheath. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath or the local interstellar Galactic cosmic ray intensity is lower than expected.     

Mediation of the solar wind termination shock by non-thermal ions

Broad regions on both sides of the solar wind termination shock are populated by high intensities of non-thermal ions and electrons. The pre-shock particles in the solar wind have been measured by the spacecraft Voyager 1 (refs 1-5) and Voyager 2 (refs 3, 6). The post-shock particles in the heliosheath have also been measured by Voyager 1 (refs 3-5). It was not clear, however, what effect these particles might have on the physics of the shock transition until Voyager 2 crossed the shock on 31 August-1 September 2007 (refs 7-9). Unlike Voyager 1, Voyager 2 is making plasma measurements. Data from the plasma and magnetic field instruments on Voyager 2 indicate that non-thermal ion distributions probably have key roles in mediating dynamical processes at the termination shock and in the heliosheath. Here we report that intensities of low-energy ions measured by Voyager 2 produce non-thermal partial ion pressures in the heliosheath that are comparable to (or exceed) both the thermal plasma pressures and the scalar magnetic field pressures. We conclude that these ions are the >0.028 MeV portion of the non-thermal ion distribution that determines the termination shock structure and the acceleration of which extracts a large fraction of bulk-flow kinetic energy from the incident solar wind.     

介质表面的辉光放电特性

为产生大面积片状等离子体,实验研究了在介质表面的直流放电氩等离子体特性. 测试了共面电极和对面电极两种结构下的放电伏安特性曲线和等离子体发光图像,讨论了介质表面效应对电场分布和放电特性的影响. 结果表明,这两种电极结构具有相似的放电特征,等离子体通道紧贴介质表面;二者伏安特性曲线基本相同,它们随放电条件的变化规律也比较相似,但与传统平板电极直流放电特性不尽相同. 介质表面影响电场分布和电荷损失机制,因而影响放电特性. 介质表面共面和对面电极结构可以产生高密度平面等离子体.     

氢等离子体特性及其对钨的辐照行为研究

本文依托四川大学直线等离子体装置(SCU-PSI)产生高通量氢等离子体,采用朗缪尔探针对氢等离子体特性进行诊断,研究了氢等离子体特性随放电电流、气体流量等输入条件的演变规律;并利用调控产生的氢等离子体对纯钨进行了相应的辐照研究. 实验结果显示, 在磁场0.1~0.2 T、气流量1 000~2 200 sccm和电流180~228 A范围内,氢等离子体通量密度、热负荷密度及电子密度、温度等参数与磁场和电流呈正相关关系,而与气体流量呈负相关关系. 在该范围内,最高等离子体密度达到2.6×1019 m-3,等离子体通量达到8.8×1022 m-2?s-1,热负荷达到6.5×104 W/m2. 利用调控产生的等离子体对纯钨样品进行初步辐照实验,结果显示随着入射等离子体特性的不同,样品表面出现不同程度的尺寸和密度不均匀颗粒状辐照损伤结构,并且颗粒尺寸随氢等离子体离子通量的增加而增大. 本文结果显示SCU-PSI可以产生理想的氢等离子体环境,因此可以作为未来聚变领域,研究氢等离子体和托卡马克装置面向等离子体材料钨以及相应结构材料相互作用的有效实验装置.     

轴向二极场MWECR—CVD系统中放电过程的静电探针测量

用静电单探针技术测定了ＭＷＥＣＲ－ＣＶＤ系统中放电过程的等离子体参数，讨论了磁场的影响。     

MEVVA离子源等离子体密度测量

采用静电探针方法测量了ＭＥＶＶＡ离子源中的等离子体，得到了单探针，双探针的特性曲线，等离子体电子温度和等离子体离子密度以及离子密度随离子源轴向的变化和径向分布。其中离子密度随离子源径向的分布近似为高斯分布，还研究了等离子体密度与弧流的关系，并采用加会切磁场的方法试图改善等离子体密度的径向分布的均匀性，得到了一些有益的结果。     

垂直激波加速中粒子动量变化的数值模拟研究

利用测试粒子数值模拟的方法统计研究了电子在垂直激波附近每次穿越过程中的动量增量随粒子速度的变化规律.模拟采用的磁场模型是由均匀的背景磁场和"slab+2D"形式的三维湍流磁场叠加构成的.数值结果表明,粒子穿越激波面前后的相对动量变化和粒子动量的相对变化率均随速度的增加而减小,当速度大于2×10~8m/s时,粒子动量的相对变化率随速度呈现更加显著的衰减趋势,明显反映出相对论参数γ=1/■所引起的物理效应.模拟结果在较大的湍流强度范围内都与理论给出的变化关系较为一致.