扩散激波加速过程中激波厚度和级联阿尔芬波对粒子加速影响的研究

通过数值求解包含二阶费米加速的一维扩散方程,探讨在准平行激波条件下激波厚度和级联阿尔芬波对粒子加速的影响,研究粒子分布函数的演化与激波厚度和阿尔芬波强度的内禀关系.计算结果表明:(1)考虑激波厚度时,谱指数明显依赖于激波厚度,随着厚度从0.32增大到2.56,低能端(3-10 MeV)谱指数逐渐从2.1增加到3.7,高能端(20-60 MeV)谱指数从2.4增大到5.0,能谱逐渐变软;当初始注入粒子动量增大1.3倍,质子能谱指数从4.3减小到3.1,且与零厚度激波加速的谱指数差值缩小;厚度不变时,随着压缩比从2增加到4,准稳态分布时低能端(3-10 MeV)粒子能谱指数逐渐从4.0减小到1.8谱变硬;(2)在级联阿尔芬波的影响下,随着时间的增大,粒子在低能处(3-10 MeV)的谱指数从2.5减小到0.6高能端(20-60 MeV)谱指数从11.6减小到5.0,能谱变硬,拐点能量值从7.5 MeV增大到为19.6 MeV;随着波的能量密度增大,谱指数从5.8减小到2.9,这表明阿尔芬波强度越大,加速效率越高.通过与激波厚度解析结果和高能粒子事件的观测能谱比较发现两者是一致的,说明数值模拟结果是可靠的.     

太阳耀斑中^3He富化的理论

概述了太阳^3He富化的一个完整的两阶段加速模型。具有适当带电状态的太阳粒子。例如^3He，电子和一些重离子主要由频率为ω=2Ω^3He的氢回旋波所加热。这些被预热的粒子进而在费米加速过程中被加速到高的能量。这一自洽的模型解释了加速的各个方面，并预言了粒子的丰度，加热离子的带电状态，以及其能谱与观测相符和的结果。     

质子耀斑爆发相的粒子加速

本文从粒子分布函数所满足的带有规则电场的准线性方程出发,得到了包含有规则电场与湍动起伏场相互耦合作用在内的等效动量空间扩散系数,提出了太阳质子耀斑中性片中的规则电场与湍动起伏场的联合加速机制。根据太阳质子耀斑的物理条件,计算表明荷电粒子在中性片中可以被有效地加速,能量可以达到～20MeV,甚至～1GeV。本文证明了离子声湍动起伏场与规则电场的联合加速机制有效地使质子和其它重离子注入到Langmuir湍动加速区中去;并且表明,在Langmuir湍动起伏场与规则电场联合加速的情形下,可以得到与观测事实符合得较好的高能质子的谱以及高能电子的幂律分布的谱。     

太阳耀斑中3He富化的理论

概述了太阳3He富化的一个完整的两阶段加速模型。具有适当带电状态的太阳粒子 ,例如3He,电子和一些重离子主要由频率为ω =2Ω3He的氢回旋波所加热。这些被预热的粒子进而在费米加速过程中被加速到高的能量。这一自洽的模型解释了加速的各个方面 ,并预言了粒子的丰度 ,加热离子的带电状态 ,以及其能谱与观测相符和的结果。     

太阳Ⅳ型分米波爆的非线性散射机制

本文提出了一种IV_(dm)型爆发的非线性散射机制和其频谱的理论计算方法.假设被捕在磁镜(IV_(dm)爆发源)的非热电子是由损失锥间隙分布所组成.非热电子(E≈500keV)激发等离子体波,经离子上的非线性散射而转换成Iv_(dm)爆发的横波.理论计算的频谱与观测符合较好,两者比较得到非热电子在源中随高度的分布以及总的IV_(dm)爆发源中的非热电子数为10~(32).另外,朗谬尔波对背景热电子有加速作用,计算v≈24vf_e的一个热电子可加速到约6MeV.可见朗谬尔湍动对电子加速是很有效的.     

射电喷流中湍动阿耳芬波对相对论电子的加速

本文通过数值求解带电粒子与Ａｌｆｖｅｎ波湍动相互作用的动力学方程，得到了相对论电子在射电喷流中被加速随时间演化的解．高能电子可以加速到Ｌｏｒｅｎｔｚ因子γｙ～１０６，且形成稳态的幂律谱，尽管其谱指数Ｓ≈ｌ比观测值小，但粒子加速时间约为１０１２－１０１４秒，小于射电斑的寿命１０７年．粒子能谱指数几乎与Ａｌｆｖｅｎ波谱指数和能量损失函数无关．能量损失对加速上限有较大影响．     

太阳IV型分米波爆的波-波非线性相互作用机制

本文提议了太阳IV_(dm)型爆发的波-波非线性相互作用机制及其频谱的数值计算方法.假设Iv_(dm)型爆发源位在太阳日冕0.6 R_⊙地方,磁场强度为4G—23G的一个磁瓶.它捕获在爆炸相期间受到加速的非热电子(E_0=100keV).这些各向异性的非热电子同时激发朗谬尔波和哨声波.这两种波的非线性结合过程产生了lV_(dm)型爆发的横波.数值计算1972,8,2,0330的频谱与观测符合较好.两者比较得到非热电子数密度随频率(高度)的分布,还得到IV_(dm)型爆发源中的平均电子数密度为372/cm~3,源中的总的非热电子数为10~(32).这比迥旋-同步加速机制所需的非热电子数少1—2量级.文中还谈到了哨声波调制朗谬尔波导致分米波爆随时间振荡的可能性.     

色球和日冕的MHD加热机制

扼要地介绍了色球和日冕加热问题的研究历史。随着空间太阳观测技术的进步，人们认识到色球和日冕加热机制主要与MHD过程有关。因此，在本文中着重介绍四种MHD色球和日冕加热机制：（1）阿尔芬波；（2）MHD湍动；（3）场向电流；（4）磁重联。由于这四种加热机制的有效性都需要通过高分辨率观测来判定，所以空间太阳观测对于研究色球和日冕加热问题具有重大意义。     

相对论电子的物理效应及其在高能天体中的应用

本文对相对论电子的辐射性质、能谱演化和加速机制等进行了简要的介绍。同时，对相对论电子在高能天体中的辐射作用和特性进行了简要的综述。本文给出了相对论电子在Blazar天体的射电辐射机制、光变机制、BL Lac天体的辐射机制以及γ暴的辐射机制等方面的应用研究成果。1、提出了相对论电子的光学薄同步辐射模型：解释Blazar天体的射电平谱：Blazar中心体的剧烈活动，使射电辐射区处于等离子体湍动状态，其中的相对论电子在湍动等离子体波的二交费米加速、激波加速、辐射损失、粒子逃逸和辐射区的绝热减速等物理过程作用下，形成较平的能谱，产生射电平谱。2、提出了新的Blazar天体光变模型：当Blazar天体爆发时，中心天体产生大量的相对论电子，注入喷流中；相对论电子产生同步辐射，并不断损失能量和逃逸辐射区，使它们的能谱快速变化，引起辐射发生快速光变。3、给出了BL Lac天体的等离子体反应堆模型：大量相对论电子从中心天体注入周围的等离子体反应堆中，通过同步辐射快速损失能量，同时这些电子同步吸收反应堆中不透明的光子，产生一个稳定、各向同性的幂律分布，其谱指数为γ＝3；然后，这些相对论电子通过等离子体反应堆的爆发或其表面扩散过程逃逸出来，辐射低频的同步辐射。模型解释了BL Lac天体的高频辐射表现出快速的谱变化性质，即流量减小时谱变陡。4、提出了相对论电子的内激波加速模型，解释γ暴的尖峰光变特性：在γ暴产生的相对论运动的壳层中，有内激波产生；激波在壳层中传播，耗散壳层的运动能，使其中的部分电子加速成为相对论电子。然后，这些电子通过同步辐射产生观测到的γ辐射。模型认为，γ暴中的每个尖峰辐射是一对内激波加速相对论电子的辐射过程，复杂的γ暴光变曲线是多对内激波辐射过程的叠加。     

一例奇特长延迟硬X射线耀斑的解释

1989年3月6日1354－1624UT的3B级大耀斑硬X射线的峰值延迟长达130秒，而硬X射线的最低能道上升至峰值的时间（上升沿）却只有150秒。在利用电子的捕获沉降模型来解释这一奇特事件，发现当日冕密度取10^9cm^-3且存在双源作用时，捕获沉降模型可以解释观测结果。     

Formation of SCR energy spectra during stochastic acceleration with allowance for Coulomb losses

The stochastic acceleration of heavy ions by Alfvén turbulence is considered with allowance for Coulomb losses. The pattern of energy dependence of these losses gives rise to characteristic features in the energy spectra of the accelerated particles at energies of the order of several MeV nucleon^?1. The manifestation of these features in the spectra is sensitive to the temperature and density of the medium, which can serve as a basis for plasma diagnostics in the flare region. Some impulsive solar energetic particle events during which features in the spectra of ³He and ⁴He were observed are considered as an example.     

Ion and relativistic electron acceleration by Alfven and whistler turbulence in solar flares

Solar Physics - We show that protons can be accelerated to several GeV in ≲10 s by Alfven turbulence whose energy density is greater than a few erg/cm3. We also show that electrons can be...     

Ion and relativistic electron acceleration by Alfven and whistler turbulence in solar flares

We show that protons can be accelerated to several GeV in 10 s by Alfven turbulence whose energy density is greater than a few erg/cm³. We also show that electrons can be accelerated to tens of MeV on similar time scales by whistler and Alfven turbulence.     

The Influences of Shock Thickness and Alfven Waves on the Particle Acceleration by Diffusive Shocks

The influences of the shock thickness and Alfven waves on the particle acceleration by diffusive shock waves are numerically studied through solving one-dimensional diffusive equation including the second-order Fermi effect. It is shown that the spectral index of the energetic particles strongly depends on the shock thickness. For example, the spectral index increases from 2.1 to 3.7 in the low energy range of 3—10 MeV and from 2.5 to 5.0 in the high energy range of 20—60 MeV as the thickness increases. The spectral index decreases from 4.3 to 3.1 as the particle injection energy increases. The spectral index decreases from 4.0 to 1.8 at the quasi-steady stage with the enhancement of the compression ratio from 2 to 4. The results indicate that under the influence of Alfven waves, the energetic particle spectrum at lower energy becomes flat and the spectral index decreases from 2.5 to 0.6 in the low energy range of 3—10 MeV and from 11.6 to 5.0 in the high energy range of 20—60 MeV. At the same time, the turning point energy reaches 19.6 MeV. The spectral index decreases from 5.8 to 2.9 as the energy density of Alfven waves increases. All these results are basically consistent with the theoretical models, as well as the observations of typical energetic particle events.     

Shock surfing acceleration

Analytical and numerical analysis identify shock surfing acceleration as an ideal pre-energization mechanism for the slow pick-up ions at quasiperpendicular shocks. After gaining sufficient energy by shock surfing, pick-up ions undergo diffusive acceleration to reach their observed energies. Energetic ions upstream of the cometary bow shock, acceleration of solar energetic particles by magnetosonic waves in corona, ion enhancement in interplanetary shocks, generation of anomalous cosmic rays from interstellar pick-up ions at the termination shock are some of the cases where shock surfing acceleration apply. Inclusion of the lower-hybrid wave turbulence into the laminar model of shock surfing can explain the preferential acceleration of heavier particles as observed by Voyager at the termination shock. At relativistic energies, unlimited acceleration of ions is theoretically possible; because for sufficiently strong shocks main limitation of the mechanism, caused by the escape of accelerated particles downstream of the shock during acceleration no longer exists.     

Particle acceleration during the explosive phase of a solar flare

Starting with the quasi-linear equation of the distribution function of particles in a regular electric field, a combined diffusion coefficient in the momentum space conbining the effects of the regular field and a turbulent field is obtained and a combined mechanism of acceleration by the regular and turbulent fields in the neutral sheet of solar proton flares is proposed. It is shown by calculation that conditions in solar proton flares are such that the charged particles can be effectively accelerated to tens of MeV, even ~1 GeV. It is shown that the combined acceleration by a regular electric field and ion-acoustic turbulence pumps the protons and other heavy ions into ranges of energy where they can be accelerated by Langmuir turbulence. By considering the combined acceleration by Langmuir turbulence and the regular electric field, the observed spectrum of energetic protons and the power-law spectrum of energetic electrons can be reproduced.     

Study of nonlinear interaction of waves through plasma-maser in magnetosphere plasma

A theoretical study is made on the generation mechanism of electrostatic Bernstein mode wave in the presence of electromagnetic Kinetic Alfven wave turbulence in magnetized inhomogeneous plasma on the basis of plasma-maser interaction. It is shown that a test high-frequency electrostatic Bernstein mode wave is unstable in the presence of low-frequency Kinetic Alfven wave turbulence. Because of the universal existence of the Kinetic Alfven waves in large-scale plasmas, the result has potential importance in space and astrophysical radiation process. The growth rate of the test high-frequency Bernstein mode wave is obtained with the involvement of spatial density gradient parameter. A comparative study on the role of density gradient in the generation of Bernstein mode on the basis of plasma-maser effect is presented.     

Kinetic Alfven waves in plasma sheet boundary layer—particle aspect analysis

The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping rate and associated currents in homogenous plasma. Kinetic effects of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (T_i/T_e) affect the dispersion relation, damping-rate and associated currents in both cases (warm and cold electron limits). The treatment of kinetic Alfven wave instability is based on the assumption that the plasma consists of resonant and non-resonant particles. The resonant particles participate in an energy exchange process, whereas the non-resonant particles support the oscillatory motion of the wave.     

Nonlinear low frequency cut-off of the spectrum of the lower hybrid magnetospheric plasma turbulence

By solving the nonlinear equation of the magnetized plasma in the weak turbulence limit the level of the spectral energy density of the lower hybrid oscillations expanding in the plasma of the Earth's polar magnetosphere, is found. As an approximation the instability which initiates turbulence is considered in a plasma with two interpenetrating beams of nonrelativistic electrons with velocities along the geomagnetic field. The saturation of the instability is due to induced scattering of the oscillations by electrons and ions of the plasma.The spectral distribution of the lower hybrid turbulence has a maximum near the low frequency boundary.     

Proton Irradiation of Centaur,Kuiper Belt,and Oort Cloud Objects at Plasma to Cosmic Ray Energy

Times for accumulation of chemically significant dosages on icy surfaces of Centaur, Kuiper Belt, and Oort Cloud objects from plasma and energetic ions depend on irradiation position within or outside the heliosphere. Principal irradiation components include solar wind plasma ions, pickup ions from solar UV ionization of interstellar neutral gas, energetic ions accelerated by solar and interplanetary shocks, including the putative solar wind termination shock, and galactic cosmic ray ions from the Local Interstellar Medium (LISM). We present model flux spectra derived from spacecraft data and models for eV to GeV protons at 40 AU, a termination shock position at 85 AU, and in the LISM. Times in years to accumulate dosages ～100 eV per molecule are computed from the spectra as functions of sensible surface depth less than one centimeter at unit density.The collisional resurfacing model of Luu and Jewitt is reconsidered in thecontext of depth-dependent dosage rates from plasma, suprathermal,and higher energy protons, and global exposure, by micrometeoroiddust grain impacts, of moderately irradiated red material below athin crust of heavily irradiated neutral material. This material should be more visible on dynamically `cold’ objects in the ～40 AU region.