射频腔光阴极注入器发射度研究

Emittance investigation of RF photoinjector

在激光驱动的光阴极注入器产生的高亮度电子束中 ,空间电荷引起发射度的增长。分析了射频腔中引起发射度增长的因素以及解决这个问题的办法——在射频腔的阴极附近加一个螺旋聚焦磁场进行补偿 ,也给出了补偿后电子束的发射度并和数值模拟结果进行比较 ,实验测试表明 ,所得结果比较符合。

A high-power laser beam illuminates a photocathode surface placed on an end wall of a RF cavity. The emitted electrons are accelerated immediately to a relativistic energy by the strong RF field in the cavity. But space charge effect induces beam emittance growth especially near the cathode where the electrons are still nonrelativistic. This paper analyzed the factors which lead the transverse emittance growth and method how to resolve this problem. After introducing solenoidal focusing near the photocathode, the beam emittance growth is suppressed dramatically. The beam emittance is given also after compensation and simulation results. The measurements show these results are coincident.