磁零点及通道宽度对霍尔推力器性能影响的数值研究

磁场位形和通道尺度会改变霍尔推力器等离子体放电过程,影响推力器的宏观放电特性.为分析磁场和通道宽度对推力器放电性能的影响规律,针对霍尔推力器轴对称通道结构和放电物理过程建立了2D3V物理模型,采用粒子模拟方法研究了霍尔推力器磁零点磁场位形不同通道宽度的电势、粒子数密度、电子温度、电离速率、比冲及推功比的变化规律.结果表...     

卫星磁层亚暴环境模拟试验设备的设计

卫星表面充电是七十年代初发现的严重危害同步轨道卫星的新问题。为了寻求解决卫星表面充电问题的方法,许多国家进行了广泛的研究。我们于82年开展卫星表面充电模拟试验技术研究。本文仅就我们在磁层亚暴环境模拟设备设计中考虑的一些问题作简要介绍。阐述了对模拟系统的要求,模拟系统的组成和用途,介绍了真空系统,电子枪,光源和测量系统设计中应考虑的问题。     

Model-independent large-scale magnetohydrodynamic quantities in magnetic clouds

Magnetic clouds are the interplanetary manifestation of coronal mass ejections, which are transient expulsions of major quantities of magnetized plasma, from the Sun toward the heliosphere. The magnetic flux and helicity are two key physical magnitudes to track solar structures from the photosphere-corona to the interplanetary medium. To determine the content of flux and helicity in magnetic clouds, we have to know their 3D structure. However, since spacecrafts register data along a unique direction, several aspects of their global configuration cannot be observed. We present a method to estimate the magnetic flux and the magnetic helicity per unit length in magnetic clouds, directly from in situ magnetic observations, assuming only a cylindrical symmetry for the magnetic field configuration in the observed cross-section of the cloud. We select a set of 20 magnetic clouds observed by the spacecraft Wind and estimate their magnetic flux and their helicity per unit length. We compare the results obtained from our direct method with those obtained under the assumption of a helical linear force-free field. This direct method improves previous estimations of helicity in clouds.     

行星际磁场与磁尾磁通量绳形成的关系

收集了Cluster卫星在2001-2005年间观测到的磁尾磁通量绳事件,并对磁通量绳(magnetic flux rope)形成及其内部磁场结构与行星际磁场(IMF)的关系作了统计研究.考虑磁通量绳被观测到时行星际磁场的条件,在所有73个磁通量绳事件中,行星际磁场By分量占有主导地位的事件有80%,且78%的事件具有与行星际磁场By分量相同方向的核心场.行星际磁场通过在磁层顶与地球磁场相互作用改变南北等离子体片内磁场相对方向,形成有利于磁通量绳形成的磁场位形,并且行星际磁场By分量的方向对磁通量绳内部核心场的方向具有决定性影响.从统计结果来看,磁通量绳的形成并不会依赖于行星际磁场Bz分量的方向.     

大气等离子加工系统设计及实验验证

建立了面向复杂光学表面的大气等离子抛光系统,并用该系统进行硅片表面加工的实验研究.研究了CF_4、SF_6两种气体的放电特性以及加工效果,得到了加工速率与功率,流量间的关系,并通过原子力显微镜观察了加工后的表面质量.     

ICP算法在地磁辅助导航中的应用

利用地磁信息进行辅助导航是组合导航技术研究的新方向。文中对地磁辅助导航的原理和发展现状进行了介绍,并在分析地磁特征的基础上,研究了利用地磁异常特征进行ICP匹配定位的方法。根据应用环境,对ICP算法进行了以下改进:首先,受模拟退火法的启发,提出采用扇形扫描法搜索最优匹配,推动ICP算法向全局最优迭代;其次,结合RANSAC法,有效地剔除了地磁测量中的野值点,提高了算法的鲁棒性。仿真结果证实了改进算法的良好性能。     

磁悬浮电机转子加强环设计及工艺研究

针对某型号磁悬浮永磁电机转子磁环胶接强度不能满足工作要求的问题，提出采用M46J／L1000复合材料缠绕加强环的保护设计方案，根据工艺实验结果，利用有限元分析软件MSC．Patran／Nastran对该结构进行应力和形变分析，并确定了合适的成形工艺参数，完成了转子加强环试验件的制作。结果表明：M46J／L1000复合材料体系满足材料组分要求，缠绕复合材料加强环结构满足磁悬浮电机转子在72000r／min高速转动时强度和变形要求。     

Temporal evolution analysis of storm-enhanced density during an intense magnetic storm on March 2015

An intense Storm Enhancement Density (SED) event with the magnetic storm occurred on 17–24 March 2015 has been investigated. The morphological character of the SED during different phase of the magnetic storm is examined and compared with the non-storm time. Three intensity indexes, i.e., “general” SED index, “heavy” SED index and “severe” SED index, are defined to represent the intensity of SED respectively represented by the numbers of the ionospheric total electron content (TEC) grids with TEC > 60 TECu, TEC > 80 TECu and TEC > 100 TECu. The temporal evolution of the SED intensity indexes during a time span covering the non-storm time and the magnetic storm time have also been investigated. The SED exhibits a shape with two parallel slender troughs in the middle and low latitudes during the non-storm time and then gradually develops into an ellipse structure as the development of magnetic storm. The intensity of SED and the fluctuation of the TEC evolution are generally corresponding to the fluctuation of Dst index. The analyzing results enrich our understanding of the temporal and spatial evolution of the ionospheric SED.     

Reconnection and fast particle production in tokamak and solar plasmas

Detailed in situ studies of magnetic reconnection and particle acceleration, which play a crucial role in the release and redistribution of energy in solar flares, can be performed in tokamak plasmas under conditions resembling those of the flaring solar corona. Recent measurements and modelling of fast particle production during reconnection events in the Mega-Amp Spherical Tokamak (MAST) are described. Specifically, observations in this device of electron acceleration during edge localised modes, and of both ion and electron acceleration during merging-compression plasma start-up, are presented, and possible implications of these studies for particle acceleration in flares are discussed. The results from MAST lend weight to the conjecture that large numbers of ions are accelerated to sub-MeV energies in flares.     

Summary of the workshop on gamma-ray burst afterglows at the 34th COSPAR meeting

A summary is given of the presentations at the COSPAR workshop on γ-ray bursts with some personal commentary on the contributions, the SN/GRB connection, and on the role of magnetic fields in γ-ray bursts and their afterglows. Of special interest were the accumulated arguments for strong collimation and associated reduction in the total required energy for γ-ray bursts. Significant discussion was also devoted to the issues associated with iron and metal lines in X-ray spectra. It is important to note that some of the afterglows seem to require ambient densities 1 g cm⁻³, rather incompatible with a massive star environment. Of associated difficulty is the fact that few, if any, afterglows seem consistent with the r⁻² wind expected for a massive star model. There are reasons to think that if γ-ray bursts are associated with supernovae they are of Type Ic. This suggests that any wind present might be rich in carbon and oxygen, not hydrogen or helium. If γ-ray bursts are narrowly collimated, then the burst is only probing a small portion of any wind, perhaps just that time-dependent and isotropic structure directly along the rotation axis. The characteristics of “hypernovae” may be the result of orientation effects in a mildly inhomogeneous set of progenitors, rather than requiring an excessive total energy or luminosity. The recent event GRB 021004 provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γ-ray burst with a massive star progenitor. If the magnetic field plays a significant role in launching a relativistic γ-ray burst jet from within a collapsing star, then the magnetic field may also play a role in the propagation, collimation, and stability of that jet within and beyond the star. The magneto-rotational instability (MRI) can operate under conditions of moderate rotation. This means that the MRI will be at work generating strong fields exponentially rapidly even as the disk of material begins to form and makes a transition from a non-Keplerian to quasi-Keplerian flow in the collapsar and related models.