离化靶中多脉冲强流电子束的不稳定性

Instabilities of multi-pulse intense electron beam in ionized target

多脉冲强流电子束轰击轫致辐射靶,在靶面形成等离子体层,将对后续电子束脉冲的稳定性产生影响。从基本等离子理论出发,利用成熟的等离子体粒子模拟程序计算在不同等离子条件下电子束流的稳定性。模拟显示在无外场情况下,当等离子体与电子束的密度比小于1时,能量20MeV、束流强度2.5kA、焦斑1.5mm的电子束出现腊肠不稳定性,但相对靶面焦点区而言,束流稳定;当密度比在1～100时,箍缩不稳定性能够改善电子束的聚焦;当密度比在100～1000时,扭曲不稳定性起主导作用,靶面焦点区电子束流仍然稳定;当密度比大于1000后,成丝不稳定性破坏束流,电子束无法在靶面聚焦。

In multi-pulse X ray photography,plasma created by earlier pulses will affect the up-coming later ones,and cause concerns on the stability of the beams.Based on the basic theory of plasma,we simulate the beam-plasma interaction and address the instability problems in different plasma density scenarios.In external magnetic field free situation,simulation shows the beam（20 MeV,2.5 kA,1.3 mm） exhibits different instability properties as the density of the plasma changes.For the density ratio of beam-plasma being less than 1,sausage instability appears,but the beam is generally undisturbed and the hotspot is good.For the density ratio of beam-plasma being between 10 and 100,the pinch effect of the plasma improves the focusing.Filamentation instabilities become prominent as the density ratio of beam-plasma is greater than 1000,the beam emittance grows rapidly,and the target hotspot is dispersed.