摘要:
为了进一步研究相对论电子束-离子通道辐射实验和理论的需要,研究了相对论电子束入射中性气体以及通过碰撞电离动态加载等离子体实现对高能束流的自聚焦传输过程PIC（particle in cell）模拟发现,电子束电离出的离子背景能够实现对电子束的聚焦传输.但是离子背景横向和纵向的不均匀性对束流的传输特性有显著影响.在此基础之上,提出了电子束在横向不均匀离子背景中传输的理论模型,给出了束流的自聚焦条件.数值计算结果表明,横向不均匀性会导致电子束的混合相位传输,使得焦点附近内层电子可能跑到电子束外而被散焦损失,这与PIC模拟的结果相符.此外,PIC模拟还发现,由于电子束的自聚焦,在焦点处将电离出更多的离子而引起纵向不均匀性,纵向不均匀性使得碰撞后的低能电子被俘获,俘获电子效应会大幅降低电子束的传输效率.但是俘获电子在纵向呈准周期分布,对传输电子起到静电Wiggler场的作用,可能实现静电Wiggler场的动态加载.研究结果对于进一步研究电子束-等离子体系统的实验以及理论模型提出有一定的参考价值.
Abstract:
In order to further study the radiation of the relativistic electron beam-ion channel experimentally and theoretically,the propagation of a relativistic electron beam in neutral gas and its self-focusing process are investigated.Particle in cell（PIC） simulation shows that the electron beam can self-focus and transmit the dynamically loaded plasma through impact ionization.The transverse and the longitude inhomogeneities of the ion background have significant effects on the transport properties of the electron beam.Base on these researches,a model of transmission of electron beam in a transverse non-uniform ion background is supposed.And the condition of self-focus is given.The numerical results show that the transverse inhomogeneity will lead to the mixed phase transmission of the electron beam,and the inner electrons can defocus near the focus point,which is consistent with the PIC simulation.The PIC simulation also shows that due to the self-focusing of the electron beam,there are much more ions to be ionized at the focus point, which will capture the lower-energy electrons after collision,the capture electron effect will significantly reduce the efficiency of the transmission of the electron beam.But the distribution of the captured electrons in the longitude direction is quasi-periodic,which acts as the electrostatic Wiggler field.These may achieve the dynamical loading of the electrostatic Wiggler field.These results give new clues to the further study of electron beam-plasma system in experiment and the establishment of theoretical models.
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