周期会切磁场聚焦强流相对论带状电子束的理论分析和粒子模拟

Propagation of intense relativistic sheet electron beam in periodic cusped magnetic fields

对低幅值、短周期、有偏置磁极的周期会切磁场中300 keV,3 kA带状电子束的传输进行了理论分析和粒子模拟。给出了将波导宽度考虑在内的轴向均匀带状电子束的空间电荷场和作用在有限厚度的带状电子束的短边和宽边上的聚焦力的表达式,并利用束匹配的方法得到了磁场的幅值和周期,以及电子束通道的宽度和高度等参数。最后根据理论计算的结果进行了3维粒子模拟验证,结果表明:束宽边上聚焦良好,而在短边上带状电子束的轴向有限长效应使得聚焦力与散焦力沿轴向不能完全匹配,在束包络上产生了Betatron振荡,但在300 mm的距离上传输效率仍能达到98%以上,说明有偏置磁极的周期会切磁场聚焦强流带状电子束在理论上是可行的。

The propagation of a relativistic（300 keV） sheet electron beam carrying high current（3 kA） through the offset-pole periodic cusped magnetic fields with low amplitude（0.173 T） and short period（20 mm） has been investigated theoretically and numerically.The expressions of the space-charge fields with finite width of the waveguide are given,followed by the expressions of the transverse focusing forces acting on the sheet electron beam with finite thickness.The amplitude and the period of the offset-pole periodic cusped magnetic fields,as well as the width and height of the beam channel,are obtained through beam matching.The 3D-PIC simulations according to the theoretical results show that,the intense relativistic sheet electron beam could be well focused in the horizontal direction,while the vertical focusing is not so good because of the betatron oscillations arising from the axial mismatch caused by the effect of axially finite length of the beam.Nevertheless,the transport efficiency is still more than 98% for the beam propagating through 300 mm.