无碰撞电流片低频电磁模不稳定性：MHD模型

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(k_z=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(k_z≠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. 关键词： 无碰撞电流片 磁流体力学 色散关系 不稳定性

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

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 (k_z=0),at the middl e 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≠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.