雷暴电场对LHAASO探测面宇宙线次级粒子能量的影响

采用Monte Carlo方法,通过模拟研究了不同强度雷暴电场对LHAASO探测面宇宙线次级电子能量的影响.在电场作用下,电子的能量分布发生了变化.在低能段总电子数目增加明显,而在高能段电场的影响不明显.当电场强度为1700V·cm-1（大于逃逸电场）时,能量<120MeV的电子被加速,能量<60MeV的总电子数目呈指数增长（增幅高达约2252%）,雷暴电场对次级粒子的加速机制与相对论电子逃逸雪崩机制（RREA）相符.当电场强度为1000V·cm-1（小于逃逸电场）时,能量<70MeV的电子被加速,其数目明显增加,但是增幅（约86%）远小于逃逸电场时的幅度.对电场强度小于逃逸电场时的雷暴电场加速宇宙线次级粒子的物理机制进行了讨论.研究结果可为理解LHAASO实验数据特点以及研究雷暴期间宇宙线强度的变化等提供参考.      

行星际磁云边界层中的电子分布函数特征

基于WIND 飞船观测的1995---2006 年间的磁云事件, 研究了磁云边界层中电子的流动图样, 以及电子速度分布函数的特点与电子加热和加速的关系, 得出以下结果. ①磁云边界层中存在的电子流动图样, 包括各向同性、双向流动和单向流动等. ② 相比于背景太阳风和磁云本体, 通常情况下磁云边界层中电子分布函数的核心热电子成分 (E<60eV) 增多, 超热电子成分 (E>60eV) 在沿磁场垂直方向上增多, 而在沿磁场平行或反平行方向以单方向增加为主, 此外, 还在近1/10 的磁云边界层中观测到了高能电子的明显增多. ③对比研究了磁云边界层与磁云驱动的激波对电子速度分布函数的调制作用, 经过激波, 电子分布函数的超热电子成分在各方向上都有增加, 不同于磁云边界层中在沿磁场平行或反平行方向上超热电子成分以单方向增加为主, 表明二者有不同的形成机制. ④考察了磁云边界层中的波活动增强和电子分布函数及离子流量增加的对应关系. 上述观测和对比分析进一步表明了磁云边界层是一种重要的动力学结构, 磁重联是一种可能的形成机制.      

倒V电子沉降通量能谱的理论计算

沿极光区磁力线大约在2000公里到8000公里的高度范围内,存在着一个等离子体湍流和大尺度平行电场的加速区。沿磁力线运动的等离子体片中的电子通过此加速区时,受到等离子体湍流和平行电场的共同作用,形成电子沉降的倒V结构。从一维准线性的动力学方程出发,导出了沉降电子通量的能谱方程,得出了电子通量能谱的理论公式。对等离子体湍流和平行电场对沉降电子能谱的影响作了分析和讨论。本文所提出的理论可以解释目前观测到的某些基本现象。      

磁场重联的二维粒子模拟研究

利用二维全粒子模拟方法研究了无碰撞等离子体中的磁场重联过程，得到了不同区域的离子和电子速度分布．计算结果表明，电子和离子在扩散区中的不同动力学特性产生的Hall电流使磁场的y分量By呈现四极形分布．离子和电子的速度分布偏离了初态时的Maxwell分布，呈现非局域的多重分布．同时由于磁场重联而产生的电场使电子在X点附近得到加速和加热，因而在电子的能谱分布中形成-高能尾。     

雷暴电场对宇宙线次级粒子中电子的影响

雷暴期间宇宙线次级粒子强度变化与大气电场的关联研究,对分析大气电场加速宇宙线次级带电粒子的机制具有重要意义.采用Monte Carlo方法,模拟研究了雷暴电场对宇宙线次级粒子中电子强度的影响.结果显示,在强度为1000V·cm~(-1)的雷暴电场中,高海拔处电子数目呈指数增长,在大气深度约300g·cm~(-2)处达到极大值,与以往研究提出的相对论电子逃逸雪崩机制相符.模拟结果表明,在地面宇宙线观测实验中,要想得到明显的观测效应,雷暴电场距离探测面的高度应600 m,电场厚度应达到约2000 m.模拟结果为分析雷暴电场与地面宇宙线次级粒子中电子强度的关联性提供了重要参考,为进一步模拟研究雷暴期间高山地面宇宙线强度的变化提供了重要信息.     

准平行无碰撞激波上游能量粒子的观测研究

通过Cluster卫星在2005年3月16日观测到的一个准平行激波观测事例,研究了准平行激波上游低频等离子体波动与能量离子之间的关系.卫星观测结果表明,在准平行激波上游,离子微分能通量受到了非线性波动的调制.在磁场强度较小区域,离子微分能通量较高.产生这种现象的可能原因是准平行激波上游的非线性波动可以捕获离子,被捕获的离子在波动中来回弹跳并被电场加速,从而导致磁场强度较小区域离子微分能通量较高.这一观测结果与已有的混合模拟结果相吻合.      

双麦克斯韦分布下极区中层尘埃粒子带电研究

在大功率微波照射下,极区中层夏季回波（PMSE）会立刻消失,该现象被称为极区中层加热现象.在大功率微波照射极区中层时,电子在微波电场加速下产生的定向运动速度与热运动速度可以比拟,极区中层的尘埃等离子体服从双麦克斯韦分布.基于双麦克斯韦分布下尘埃粒子充电理论给出极区中层尘埃粒子的电荷分布,比较了大功率微波对极区中层加热前和加热时,尘埃粒子电荷以及极区中层电子浓度的变化.结果表明,采用大功率微波装置加热极区中层会影响电子对尘埃粒子的充电进而导致电子浓度变化,这对解释极区中层加热现象具有重要意义.      

磁化等离子体中斜传播的离子孤波

近几年卫星空间电场测量经常证认出局地非线性离子静电波,它们可能与极光粒子加速有直接关系。这些静电波被认为或者是离子声波模的演化,或者是静电离子逥旋波模的演化结果。本文研究了磁场中斜传播小振幅离子非线性波的演化,得到非线性Schrodinger方程。结果表明离子声孤波和离子迴旋孤波都是可能的。计算结果与卫星S(3-3)电场测量比较,可以很好说明部分测量结果。      

存在初始引导场情况下的无碰撞磁场重联

采用二维三分量的全粒子模拟方法研究了不同初始引导场情况下的无碰撞磁场重联及初态为一维的Harris电流片.结果表明,Bz0＞0.5B0的强引导场不仅会显著改变粒子的运动轨迹,而且会改变重联区附近的电场和流场结构,从而影响重联率和电子加速.运用广义欧姆定律解释了不同引导场下电场的结构特征.另外,通过对扩散区附近束流电子的跟踪研究发现,在二维模型中,不论引导场强弱,位于扩散区中心垂直模拟平面的感应电场对电子加速起主要作用,而扩散区外平面电场的贡献很小.      

真空中连续发射电子束形成的电子鞘层的空间结构

用双流理论模型研究真空中电子束的发射实验。向真空中发射电子束过程中,发射体本身被充正电,束缚束电子向外传播,大量的束电子在发射体表面附近形成电子鞘层;只有极少量的束电子可以逃离发射体而向外传播出去。在电子鞘层内,发射出的束电子和返回发射体表面的束电子形成速度和密度在空间为分布不均匀的双流。本文用双流理论模型解析计算出了电子鞘层的空间尺度、电子鞘层内的电场分布以及电子密度分布。      

太阳高能电子束通过空间振荡轴向场产生的电磁不稳定性

本文基于太阳高能电子和日冕区开放场及行星际磁场特征，建立了相对论电子束与伴有空间变化（空间周期变化）的轴向场相互作用模型，用数值方法研究了该体系产生的电磁不稳定性，结果指出只有当太阳高能电子束速度和空间振荡场波数大到一定程度时，该体系才可激发在旋电磁模不稳定性，当太阳高能电子束逐一通过日冕和行星际空间时，激发具有波频向低频漂移特征的电磁波．     

离子迴旋波的参量激发

本文分析了极光区上空以低混杂波作为泵波激发静电离子迴旋波的可能性,并计算了增长率。结果表明,当泵波较强时(峰值100mV/m)增长率可达0.5ω_ci,大于电流驱动不稳定性及离子束流不稳定性等线性理论所可能期待的增长率。从而在某些情况下,离子迥旋波的这种参量激发可能是主要的。      

New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. In the initialisation of the beam-plasma system, “quiet start” conditions were approached by including the poloidal magnetic field due to the current carried by beam electrons streaming along a background magnetic field. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, (2) the parallel phase velocity of the whistler wave is smaller than that of the beam mode, and (3) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is involved in the generation of the whistler waves.     

电离层中SEE现象的静电粒子模拟

利用网格粒子云（PIC）模型。在一定条件下，对电离层加热实验中静电波的激发和参量不稳定性的产生，作一维静电粒子模拟，模拟结果表明，SEE的特征与加热泵波频率ω0和电子回旋频率nωce之间的比值有关。入射泵波的电场与地磁场之间的夹角也是影响SEE的一个因素。     

Electron acceleration and parallel electric fields due to kinetic Alfvén waves in plasma with similar thermal and Alfvén speeds

We investigate electron acceleration due to shear Alfvén waves in a collissionless plasma for plasma parameters typical of 4–5R_E radial distance from the Earth along auroral field lines. Recent observational work has motivated this study, which explores the plasma regime where the thermal velocity of the electrons is similar to the Alfvén speed of the plasma, encouraging Landau resonance for electrons in the wave fields. We use a self-consistent kinetic simulation model to follow the evolution of the electrons as they interact with a short-duration wave pulse, which allows us to determine the parallel electric field of the shear Alfvén wave due to both electron inertia and electron pressure effects. The simulation demonstrates that electrons can be accelerated to keV energies in a modest amplitude sub-second period wave. We compare the parallel electric field obtained from the simulation with those provided by fluid approximations.     

太阳风质子束流的演化

太阳神飞船观测表明，太阳风高速流中质子束分量相对于核分量的密度随日心距离增加而增加．提出解释这一观测现象的机理并给出二维数值模拟结果．由于阿尔芬波速随日心距离增加而减少，第二支左旋波将与更多的质子共振，把部分原来属于核分布的质子拉到束分布中来．用数值模拟方程方法求解回旋波共振导致的准线性扩散方程，数值结果与观测结果相符合．     

Origin and energetics of the Io plasma torus

The ionization of the gas ejections from the Io satellite into the Jovian magnetosphere by the corotating magnetospheric plasma flow is considered. It is shown that the plasma flow velocity at the Io orbit exceeds the critical velocity at which the anomalous electron ionization of the heavy gas components takes place due to collisionless energy transfer from ionized gas atoms to plasma electrons. The energy, number density and spatial distribution of suprathermal electrons is calculated using the quasilinear theory of newly ionized atoms instability in a moving plasma. Saturation of the plasma density build up in a plasma is considered in terms of the instability quenching by Coulomb collisions.     

Analysis of the turbulence observed in the outer cusp turbulent boundary layer

One of the prominent features of the cusp Turbulent Boundary Layer (TBL) is a persistent low frequency electromagnetic turbulence that extends from <1Hz up to the electron cyclotron frequency, accompanied by what appears to be purely electrostatic noise above this frequency range. The Plasma Wave Instrument onboard Polar obtained plasma wave measurements in the cusp TBL in the form of waveform captures simultaneously from 6 different sensors (3 each orthogonal electric and magnetic) in the frequency range 1 Hz up to 25 kHz. This allowed us to directly calculate the phase velocity from the measured ratio of |dE| to |dB| and compare it to theoretical values for various modes. Using this technique, we have gained some insight into the mode of the electromagnetic turbulence that extends in frequency from 1 Hz up to the electron cyclotron frequency (several hundred Hz to a few kHz) in the TBL. The whistler and kinetic Alfvén wave modes are discussed as the possible modes of this turbulence. By analyzing the high time resolution waveforms, we isolate and identify some of these modes. The electrostatic turbulence above the electron cyclotron frequency is associated with pulses and quasi-sinusoidal waveforms observed in the measured time series. These do not fit any known mode, although work is continuing in this area to show that some of them may be associated with electron holes or with downshifted Langmuir waves produced through a two-stream instability.     

强磁场中电磁辐射散射的自激效应

电子在磁场中运动,对频率ω_i的外来电磁波的散射,除频率仍为ω_i的部分以外,还发出与回旋辐射相同频率的散射波,这可以称作是自激效应.除了高频极限,该效应对散射截面有相当大的影响.本文对单个电子及冷等离子体情形,给出了强磁场中非相对论性经典电子散射截面的修正计算.讨论了电子散射的谱分布,给出某些典型情形中平衡状态下磁等离子体的Thomsom吸收系数.本文结果可应用于X射线脉冲星谱线形成等问题.      

Electromagnetic ion cyclotron resonance heating in the VASIMR

Plasma physics has found an increasing range of practical industrial applications, including the development of electric spacecraft propulsion systems. One of these systems, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine, both applies several important physical processes occurring in the magnetosphere. These processes include the mechanisms involved in the ion acceleration and heating that occur in the Birkeland currents of an auroral arc system. Auroral current region processes that are simulated in VASIMR include lower hybrid heating, parallel electric field acceleration and ion cyclotron acceleration. This paper will focus on using a physics demonstration model VASIMR to study ion cyclotron resonance heating (ICRH). The major purpose is to provide a VASIMR status report to the COSPAR community. The VASIMR uses a helicon antenna with up to 20 kW of power to generate plasma. This plasma is energized by an RF booster stage that uses left hand polarized slow mode waves launched from the high field side of the ion cyclotron resonance. The present setup for the booster uses 2–4 MHz waves with up to 20 kW of power. This process is similar to the ion cyclotron heating in tokamaks, but in the VASIMR the ions only pass through the resonance region once. The rapid absorption of ion cyclotron waves has been predicted in recent theoretical studies. These theoretical predictions have been supported with several independent measurements in this paper. The ICRH produced a substantial increase in ion velocity. Pitch angle distribution studies show that this increase takes place in the resonance region where the ion cyclotron frequency is equal to the frequency on the injected RF waves. Downstream of the resonance region the perpendicular velocity boost should be converted to axial flow velocity through the conservation of the first adiabatic invariant as the magnetic field decreases in the exhaust region of the VASIMR. In deuterium plasma, 80% efficient absorption of 20 kW of ICRH input power has been achieved. No evidence for power limiting instabilities in the exhaust beam has been observed.