Bret A, Firpo M-C, Deutsch C
Laboratoire de Physique des Gaz et des Plasmas (CNRS-UMR 8578), Université Paris XI, Bâtiment 210, 91405 Orsay cedex, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Oct;70(4 Pt 2):046401. doi: 10.1103/PhysRevE.70.046401. Epub 2004 Oct 4.
We investigate the linear stability of the system formed by an electron beam and its return plasma current within a general framework, namely, for any orientation of the wave vector k with respect to the beam and without any a priori assumption on the orientation of the electric field with respect to k . We apply this formalism to three configurations: cold beam and cold plasma, cold beam and hot plasma, and cold relativistic beam and hot plasma. We proceed to the identification and systematic study of the two branches of the electromagnetic dispersion relation. One pertains to Weibel-like beam modes with transverse electric proper waves. The other one refers to electric proper waves belonging to the plane formed by k and the beam, it divides between Weibel-like beam modes and a branch sweeping from longitudinal two-stream modes to purely transverse filamentation modes. For this latter branch, we thoroughly investigate the intermediate regime between two-stream and filamentation instabilities for arbitrary wave vectors. When some plasma temperature is allowed for, the system exhibits a critical angle at which waves are unstable for every k . Besides, in the relativistic regime, the most unstable mode on this branch is reached for an oblique wave vector. This study is especially relevant to the fast ignition scenario as its generality could help clarify some confusing linear issues of present concern. This is a prerequisite towards more sophisticated nonlinear treatments.
我们在一个通用框架内研究由电子束及其返回等离子体电流形成的系统的线性稳定性，即对于波矢(k)相对于束流的任何取向，且不对电场相对于(k)的取向做任何先验假设的情况。我们将这种形式体系应用于三种配置：冷束流和冷等离子体、冷束流和热等离子体以及冷相对论束流和热等离子体。我们着手对电磁色散关系的两个分支进行识别和系统研究。一个分支属于具有横向电本征波的类韦贝尔束流模式。另一个分支指的是属于由(k)和束流所构成平面的电本征波，它在类韦贝尔束流模式和一个从纵向双流模式延伸到纯横向丝状模式的分支之间划分。对于后一个分支，我们深入研究了任意波矢下双流不稳定性和丝状不稳定性之间的中间区域。当考虑一定的等离子体温度时，该系统呈现出一个临界角，在这个临界角下，对于每个(k)，波都是不稳定的。此外，在相对论区域，该分支上最不稳定的模式是由一个倾斜的波矢达成的。这项研究对于快速点火方案尤为重要，因为其通用性有助于澄清当前一些令人困惑的线性问题。这是进行更复杂非线性处理的一个先决条件。
