对大回旋半径电子枪的渐变线圈磁场进行了设计, 采用3个线圈实现所需要的渐变磁场分布, 增加了线圈磁场系统的调节能力, 理论和计算机仿真的磁场分布结果符合得很好。将实现的渐变磁场分布同给定的静电场分布相结合, 通过求解带电粒子的运动方程得到了粒子轨迹, 在此基础上建立大回旋半径电子枪的3维粒子仿真模型, 在给定静电场分布条件下分析了3个线圈安匝数对电子束参数的影响, 完成了工作电压为40 kV、工作电流为1 A的大回旋半径电子枪的参数优化, 得到了横纵速度比为1.4～2.5, 纵向速度离散小于8%(横纵速度比为1.9时)的大回旋半径电子束。

This paper studies the smooth cusp magnetic field for an axis-encircling large-orbit electron gun, which is realized by three different coils. Theoretical analysis and computer simulation of the field distribution agree well with each other. The Lagrangian for the electron is used to deduce the electron’s equations of motion. The trajectories of electrons are then numerically calculated with the equations and the result is consistent with that of the three-dimensional particle-in-cell simulation. Through optimization of the ampere turns of the three coils, the velocity ratio from 1.4 to 2.5 and the axial velocity spread below 8% (at the velocity ratio equal to 1.9) are obtained with a 40 kV, 1 A electron beam.