能量粒子进入磁层的数值模拟研究

来自行星际的能量粒子进入磁层的过程一直是磁层研究的热点,也是空间天气研究关注的焦点之一,而以往的工作大都集中在讨论不同行星际条件下粒子进入磁层的统计规律.本文在T89磁层模式的基础上,建立了太阳能量粒子进入磁层运动的程序,计算了几种不同能量的质子从不同方位角入射到磁层的运动轨迹.模拟结果表明,能量粒子沿着磁力线方向才可能穿越磁层到达地球表面,越偏离这个方向,则越早被反弹.能量越高的粒子进入到地球磁层上空的角度范围越大,但仍然只有沿着磁力线入射的粒子才能到达地球表面.这些结果与理论预言是一致的.      

Acceleration and transport of energeticparticles at CME-driven shocks

Historically, solar energetic particle (SEP) events are classified in two classes as “impulsive” and “gradual”. Whether there is a clear distinction between the two classes is still a matter of debate, but it is now commonly accepted that in large “gradual” SEP events, Fermi acceleration, also known as diffusive shock acceleration, is the underlying acceleration mechanism. At shock waves driven by coronal mass ejections (CMEs), particles are accelerated diffusively at the shock and often reach > MeV energies (and perhaps up to GeV energies). As a CME-driven shock propagates, expands and weakens, the accelerated particles can escape ahead of the shock into the interplanetary medium. These escaping energized particles then propagate along the interplanetary magnetic field, experiencing only weak scattering from fluctuations in the interplanetary magnetic field (IMF). In this paper, we use a Monte-Carlo approach to study the transport of energetic particles escaping from a CME-driven shock. We present particle spectra observed at 1 AU. We also discuss the particle “crossing number” at 1AU and its implication to particle anisotropy. Based on previous models of particle acceleration at CME-driven shocks, our simulation allows us to investigate various characteristics of energetic particles arriving at various distances from the sun. This provides us an excellent basis for understanding the observations of high-energy particles made at 1 AU by ACE and WIND.     

磁扰期间的三维漂移壳分离

基于磁层粒子动力学理论,首先对比了计算漂移壳分离的引导中心法和磁力线追踪法,计算表明两种方法的计算结果一致.然后分别采用T89c和T96磁层磁场模式,用磁力线追踪法数值计算了不同初始位置(≤9Re)、不同初始投掷角、不同Kp指数和不同太阳风压力下,带电粒子的漂移壳分离.计算结果揭示了漂移壳分离随初始位置、投掷角、Kp指数和太阳风压力的变化.其具体特征如下. (1)随着径向距离的增大,漂移壳分离效应愈加显著,由正午出发的粒子将被稳定捕获,而午夜出发的径向距离≥7Re的部分大投掷角粒子将沿磁层顶逃逸. (2)正午出发的粒子,漂移到午夜时其漂移壳随投掷角减小向外排列;午夜出发的粒子,漂移到正午时其漂移壳随投掷角增大排列; 90°投掷角粒子在磁赤道面的漂移壳沿着磁场等值线排列. (3)漂移壳分离随Kp指数和太阳风压力增大变得显著,且随这两种扰动参数的变化特征和趋势是基本相似的.      

Solar wind and its interaction with the magnetosphere: Measured parameters

The earth's magnetosphere absorbs only a minor fraction (≈ 10^?3) of the incident solar wind energy. Variations of the solar wind can often cause lively reactions in the earth's close environment. However, the physical mechanisms involved are not yet understood. It appears now that the combined action of the solar wind momentum flux, the direction of the interplanetary magnetic field as well as its fluctuations might play the dominant role. The behaviour of these parameters is governed in some characteristic way by the solar wind stream structure which reflects the condition of the solar corona and its magnetic field topology. Transients in the sun's atmosphere associated with solar activity cause reactions in the interplanetary medium which also show some typical, though very different, signatures. Taking into account the interdependence of the solar wind parameters in context with the underlying solar phenomena, we may be able to pinpoint the mechanism which controls the action of the solar wind on the magnetosphere.     

磁尾粒子在晨昏电场作用下的散射与沉降

我们认为,在沉降粒子的形成中,磁尾粒子的散射是极其重要的。本文从粒子的轨道理论人手,通过对近900条粒子轨道的具体计算,研究了磁尾粒子在晨昏电场作用下的投掷角变化。计算结果清楚地显示出了磁尾粒子在晨昏电场的作用下,经历着明显的散射过程。运动经过非小扰动区的磁尾粒子在非小扰动区内经多次反射,磁矩不再是不变的,从而投掷角改变,使得一个原在磁尾为各向同性的投掷角分布,在粒子运动到远离中性线的近地区域时改变成为一个近麦氏分布。我们还研究了这些粒子的空间经历,发现这些离开磁尾进入近地区域的粒子在发生散射的同时还发生了空间分离——晨昏分离、纬向分离以及质子和电子之间的相对空间分离,给出了清晰的粒子沉降图象。      

Propagation of upstream protons in the near-earth solar wind

The propagation of energetic protons (35–1600 keV) from the Earth's magnetosphere to the ISEE-3 spacecraft located about 240 earth radii (R_E) upstream in the solar wind is used as a tool to study the interaction between these protons and the solar wind. In this preliminary study we present proton pitch angle distributions seen at different times during the development of upstream events that occur in relatively quiet interplanetary conditions. In general a highly anisotropic sunward flow is seen at the beginning of the events. During the course of the events pitch angle distributions may vary between streaming along the field lines (peaked around 0° pitch angle), a uniform intensity between 0° and 90°, and a peaked distribution around a preferred pitch angle that is often near 90°.     

Dust grain orbital behavior around ceres

Many asteroids show indications they have undergone impacts with meteoroid particles having radii between 0.01 m and 1 m. During such impacts, small dust grains will be ejected at the impact site. The possibility of these dust grains (with radii greater than 2.2 μm) forming a halo around a spherical asteroid (such as Ceres) is investigated using standard numerical integration techniques. The orbital elements, positions, and velocities are determined for particles with varying radii taking into account both the influence of gravity, radiation pressure, and the interplanetary magnetic field (for charged particles). Under the influence of these forces it is found that dust grains (under the appropriate conditions) can be injected into orbits with lifetimes in excess of one year. The lifetime of the orbits is shown to be highly dependent on the location of the ejection point as well as the angle between the surface normal and the ejection path. It is also shown that only particles ejected within 10° relative to the surface tangential survive more than a few hours and that the longest-lived particles originate along a line perpendicular to the Ceres-Sun line.     

ROSAT all-sky-survey detections of classical novae and related objects

In the ROSAT all-sky-survey 7 classical novae were detected, but only 1 of the 26 that had an outburst in the 10 years before the survey. 3 are new X-ray detections; 1 source is a known intermediate polar and 4 are suspect “magnetic novae”. 3 objects show a very soft spectrum. Among the objects related to novae we found 2 dwarf-novae with unusually long periodicity, the peculiar source KR Aur and 4 X-ray novae. One of these, V404 Cyg, was detected at quiescence for the first time.     

Cosmology and GUTs: The matter of the universe

To illustrate the interaction of Grand Unified Theories (GUTs), supersymmetry (SUSY), and cosmology, a worked example is carried out. This example is the dark matter problem, or “What is the dominant matter of the Universe?” It is shown that if GUTs are assumed then the primordial perturbations are probably adiabatic, if inflation is assumed then Ω = 1 and GUTs first name is probably SUSY. If Ω = 1, big bang nucleosynthesis tells us that the bulk of the matter is non-baryonic. SUSY-GUTs gives us some possible candidate inos to which massive neutrinos, axion or planetary mass black holes can be added. These candidates can be classified hot (or warm) or cold types of dark matter. It is shown that hot gives Ω = 1 and naturally gives large scale structure but does not give small scale structure or galaxy formation times, whereas cold gives small scale structure and formation times but cannot easily yield Ω = 1. It is concluded that either a hybrid of both hot and cold or non-random phases for the perturbations may be needed.     

Optical and X-ray aspects of quasars

We review the present knowledge on the cosmological evolution of quasars, by discussing some of the recent results obtained from studies of optically selected objects. Despite the fast development of prism survey tecniques, the color selection still appears to be the best tecnique for constructing the complete samples which are necessary for statistical studies. It is shown, however, that even the best available complete samples of quasars selected on the basis of ultraviolet excess (z < 2.2) are not sufficient to univocally determine the “correct” evolutionary model. Moreover, some preliminary results suggest that the evolution law derived from quasars with m_B<20 and z<2.2 can not be extrapolated to fainter magnitudes and higher redshifts. On the basis of what is known today about the optical and X-ray properties of quasars, we then discuss some of teh possible results, relevant to cosmology, which can be achieved with future coordinated optical and X-ray observations of quasars.     

Prognoz-6 data about ultraviolet sky background in dark and Milky Way regions of the sky

Ultraviolet spectra (1100–1900 Å) of the sky background of 10 wide angle (6°×6°) regions obtained between 70 000 km and 200 000 km from the Earth with the photoelectric spectrometer “GALACTIKA” on board the satellite “PROGNOZ-6” are considered. The spectral energy distribution of the sky background, after subtraction of the stellar component, is similar for regions on both sides of the Milky Way and exhibits a strong U.V. light contribution. On the contrary, the Milky Way (l_II=190° b_II=+6°) is less rich in far U.V. light; this can be related to the predominance of an expected selective absorption near the galactic plane. The nature of U.V. excess at high galactic latitudes needs further investigations.     

Investigation of magnetospheric processes with the use of a source of strong magnetic field in the ionosphere

More than 20 years ago V.P. Shabansky suggested that the magnetic system installed aboard the satellite, could be used as a physical instrument for studying the processes which occur in the near Earth space. The corresponding space scales of an artificial “magnetosphere”—“magnisphere”—are 10 m in the experiment with relatively small magnets in the ionosphere and 100 m in the solar wind. The corresponding similarity criteria are estimated. The possible scheme of the experiment with a superconducting magnet (magnetic moment 10⁵ A · m²) installed aboard the satellite is considered. The experimental complex includes a number of systems for measuring the fluxes of charged particles in a wide energy range, DC electric and magnetic fields, the electromagnetic fields in different frequency bands (from X-rays to radio). The scientific objectives are discussed in detail.     

月表磁异常影响的太阳风电子反射运动

模拟太阳风电子向月表运动的轨迹, 研究由于月表磁异常的存在造成的电子反射运动. 首先设定行星际磁场Bsw 指向月球并与月表垂直, 将月表的磁异常区看成是一个磁偶极子, 偶极矩大小为Mcb; 然后分别考察该偶极矩与行星际磁场方向平行, 反平行以及±90° 的情形, 通过计算发现, 被反射的电子数目会随着磁偶极矩和行星际磁场的方向改变而改变. 在偶极矩与行星际磁场平行的情况下, 反射率最大; 随着夹角的增大, 反射率减小. 这些结果为利用电子反射法高精度遥测月表磁场提供了很重要的信息.      

Mini-belt as a fine spatial structure of the outer radiation belt in quiet and disturbed conditions

Electron flux data from LANL geostationary spacecrafts were statistically treated and ordered in a special magnetic coordinate system (effective L-coordinate and MLT). The data treating procedure allowed to obtain the dynamics of quasi-trapped electrons of different energies on effective L-shells ranging from 6.6 to 7.0. It was found that in quiet conditions a stable fine spatial structure of quasi-trapped electrons exists with maximum of fluxes near L = 6.78 and MLT=12. This structure may be looked at as an asymmetrical “mini-belt”. The position of the maximum depends on electron energy and changes with magnetic activity. The dynamics of this mini-belt for both quiet and disturbed periods is illustrated and discussed. During isolated magnetic storms the mini-belt maximum shifts in a regular manner outward and inward; a diffusion wave of quasi-trapped particles propagates from outside of the geostationary orbit and serves as a source of new particles for the mini-belt. The azimuthal geometry of this diffusion wave extracted from experimental data is illustrated. The possible role of the “mini-belt” is discussed in relation with well-known “anomalous” dynamics of the inner radiation belt.     

Antiparticle content in the magnetosphere

In the present work we assess the stable and transient antiparticle content of planetary magnetospheres, and subsequently we consider their capture and application to high delta-v space propulsion. We estimate the total antiparticle mass contained within the Earth’s magnetosphere to assess the expediency of such usage. Using Earth’s magnetic field region as an example, we have considered the various source mechanisms that are applicable to a planetary magnetosphere, the confinement duration versus transport processes, and the antiparticle loss mechanisms. We have estimated the content of the trapped population of antiparticles magnetically confined following production in the exosphere due to nuclear interactions between high energy cosmic rays (CR) and constituents of the residual planetary upper atmosphere.The galactic antiprotons that directly penetrate into the Earth’s magnetosphere are themselves secondary by its nature, i.e. produced in nuclear reactions of the cosmic rays passing through the interstellar matter. These antiproton fluxes are modified, dependent on energy, when penetrating into the heliosphere and subsequently into planetary magnetospheres. During its lifetime in the Galaxy, CR pass through the small grammage of the interstellar matter where they produce secondary antiprotons. In contrast to this, antiprotons generated by the same CR in magnetosphere are locally produced at a path length of several tens g/cm² of matter in the ambient planetary upper atmosphere. Due to the latter process, the resulting magnetically confined fluxes significantly exceed the fluxes of the galactic antiprotons in the Earth’s vicinity by up to two orders of magnitude at some energies.The radiation belt antiparticles can possibly be extracted with an electromagnetic-based “scoop” device. The antiparticles could be concentrated by and then stored within the superimposed magnetic field structure of such a device. In future developments, it is anticipated that the energy of the captured antiparticles (both rest energy and kinetic energy) can be adapted for use as a fuel for propelling spacecraft to high velocities for remote solar system missions.     

Synchrotron radiation as a probe of the inner magnetosphere of Jupiter

A short review is given on the characteristics of Jupiter's inner magnetosphere derived from radio observations in the decimetric wavelength range. A comparison of the data with sophisticated model calculations yields information on the magnetic field configuration and the electron distribution, its density, energy spectrum, and pitch angle dependence as a function of spatial coordinates. The latter information can be used to derive e.g. the radial diffusion parameters plus the effects of the satellites, Jupiter's ring, and wave-particle interactions upon the electron distribution.     

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.     

Solar flare proton release from coronal magnetic traps and strong Alfvén turbulence in the corona

Drift instabilities arising when accelerated protons are trapped by coronal magnetic fields of active regions are investigated theoretically. If β, the ratio of total (plasma + energetic particles) pressure and magnetic field pressure is larger than some value, $\text{β?0.1}\text{to}\text{0.3}$, the magnetic trap is destructed and protons are released into interplanetary space. If $\text{β < β}{}^1$, the trapped protons excite gradient instability due to magnetic drift resonance. This “universal” instability results in rapid development of strong Alfvén wave turbulence with small wavelengths transverse to the magnetic field. Particle diffusion due to the waves has a rather complicated character and appears to be weak as compared to quasilinear diffusion. The role of Alfvén waves may consist in additional heating of the corona in the regions of closed magnetic field lines.     

Experimental drop tube of the metallurgy department of Grenoble

The drop tube which will be available in the “Centre d'Etudes Nucléaires de Grenoble” is described. Its main features are the following: - Dimensions : Drop height : 47.1 m Drop time : 3.1 s Tube inside diameter : 0.2 m - Experimental atmosphere : 1 Ultra-vacuum : 10⁻⁶ to 10⁻⁷ Pa - Residual gravity level : 10⁻⁸ to 10⁻⁹ g according to the vacuum level and drop diameter.

This facility is unique insofar as it enables experiments to be performed under ultra-vacuum conditions which, by delaying the formation of surface oxides, should contribute to improving maximum undercooling values.

The techniques used for obtaining small metallic drops (0.5 to 3 mm) are described. The availability of this instrument for the scientific community is also foreseen by the french sponsoring organizations (CEA, CNES, CNRS) ; some practicle informations will be given to potential experimenters.