调制电子束在空间等离子体中激发的电磁波辐射

Electromagnetic wave excitation by the modulated electron beam in the space plasma

当调制电子束入射进空间等离子体时,由于电子束本征电磁场在非均匀等离子体中的散射(渡越辐射transitionradiation)或者电子束的纵向约束性可以产生电磁波辐射。基于这两种辐射机制,研究了半无界调制电子束从航天器入射进平面分层各向同性非均匀空间等离子体产生的电磁波辐射。结果表明,由背景等离子体非均匀性产生的电磁波辐射强度高于由束的纵向约束性引起的辐射强度通过对电子束的适当调制,可以满足辐射电磁波在局部等离子体谐振区域的共振条件,从而增大辐射强度。研究结果可用于对主动空间等离子体试验数据的分析。

When modulated electron beams are injected to the space plasma, electromagnetic waves are excited either because of longitudinal restriction of electron beams, or because of transition radiation of electromagnetic eigenmodes of electron beams in inhomogeneous plasma. In this paper, the excitation of electromagnetic waves produced by these two mechanisms is studied when semi-restricted modulated electron beams are injected from spacecraft into the level-layered isotropic inhomogeneous plasma. The results from numerical calculation show that the excitation created by the latter mechanism is stronger than that created by the former. By properly modulating the electron beam, the resonance condition of radiated electromagnetic waves in local plasma can be satisfied and thereby increase the radiation intensity. This result can be used to analyze the experimental data collected in the active plasma experiments in space.