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  

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

作　　者：朱庆利[1] 吴桂平[1] 孔德泉 

机构地区：[1]东南大学物理系,南京211189

出　　处：《天文学报》2009年第1期45-53,共9页Acta Astronomica Sinica

基　　金：国家自然科学基金(10773032;10833007)资助项目

摘　　要：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.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---450 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 rollover energy reaches 19.6 MeV. The spectral index decreases from 5.8 to 2.9 as the energy density of Alfven waves increase. All these results are basically consistent with the theoretical models, as well as the observations of typical energetic particle events.

关 键 词：日-地关系 物理数据与过程:粒子的加速 激波 波 

分 类 号：P142[天文地球—天体物理]