无碰撞电流片低频电磁模不稳定性:MHD模型  

Low-frequency electromagnetic instabilities in a collisionless current sheet:magnetohydrodynamic model

作　　者：魏新华[1,2] 周国成[1] 曹晋滨[1] 李柳元[1,2] 

机构地区：[1]中国科学院空间科学与应用研究中心 [2]中国科学院研究生院,北京100039

出　　处：《物理学报》2005年第7期3228-3235,共8页Acta Physica Sinica

基　　金：国家杰出青年科学基金(批准号:40025413);国家自然科学基金(批准号:40174042)资助的课题.~~

摘　　要：利用含无电阻广义Ohm定律的可压缩磁流体力学(MHD)理论,研究了在具有剪切磁场的无碰撞电流片中低频电磁模不稳定性,假定等离子体压力各向同性,推导出了三维扰动传播波模的色散关系.色散关系的数值求解集中在电流片中间平面(z=0)和半厚度边缘(z=1)上,并分别考虑了二维传播和三维传播,以及不同的离子惯性长度情况.主要结果如下:1)对于二维扰动传播(kz=0)的波,在z=0平面上,Alfven波增长率最大,不稳定的波频率和波数范围也更宽.离中间平面越远,增长率越小,波数区域越小.同时,随着离子惯性长度的增大,Alfven波不稳定性的增长率变大.2)对于三维扰动传播(kz≠0)的波,哨声是不稳定的.在电流片中间平面上,哨声有明显的增长率;而在离子惯性区外边,哨声的增长率还变大.3)在电流片中间(z=0)平面上,低频波主要是电流不稳定性激发的.在离中间平面较远处,电流、密度和压力的梯度不稳定性变得更重要.Low-frequency electromagnetic instabilities in a collisionless current sheet are discussed by using the 3-dimensional, collisionless and compressible magnetohydrodynamic model with the isotropic pressure. The linear dispersion relations are numerically solved at the middle plane (z = 0) and edges (z = 1) of the current sheet for modes of 2-and 3-dimensional propagation. The main results are as follows. (1) For 2-dimensional disturbed propagation on (k(z) = 0), at the middle plane (z = 0), the growth rate of Alfven waves is maximum, and the frequency and the wavenumber region of unstable waves are widest. The farther the distance from the middle plane, the smaller the growth rate and the wavenumber region. As the ion-inertial length becomes longer, the growth rate of Alfven waves becomes larger. (2) For 3-dimensional disturbed propagation (k(z) not equal 0), whistler waves are unstable. At the current sheet middle plane, whistler waves have an obvious growth rate. Outside the ion-inertial region, the growth rate of whistler waves becomes larger. (3) At the middle plane (z = 0), low-frequency waves are mainly excited by the current-driven instabilities. At places far from the middle plane, the gradient instabilities of the current, density and pressure become more important.

关 键 词：不稳定性 电流片 无碰撞 MHD模型 电磁 ALFVEN波 等离子体压力 扰动传播 色散关系 磁流体力学 各向同性 数值求解 三维传播 波增长率 平面 中间 可压缩 哨声 惯性区 低频波 二维 长度 波数 定律 磁场 波模 梯度 

分 类 号：O53[理学—等离子体物理]