基于会切磁场的理论模型，采用粒子模拟软件对0.6 THz三次谐波的太赫兹回旋管所需的大回旋电子光学系统进行研究。通过大量的模拟计算，分析讨论了不同参数对电子注的横向速度离散、纵向速度离散及横纵速度比的影响，优化了电子光学系统的性能参量，得到符合设计要求且具有工程实际应用的电子枪，该电子枪能够产生55 kV，1 A，横向速度离散为3.39%、纵向速度离散为7.10%、横纵速度比为1.53的大回旋电子注。

Large orbit axis-encircling electron beams can provide improved coupling and mode selectivity in a high harmonic terahertz gyrotron. For developing a 0.6 THz 3rd-harmonic large orbit gyrotron, a cusp gun with a beam voltage of 55 kV and a beam current of 1 A has been designed based on a comparatively simple Pierce-type electron gun and cusp magnetic field. The optimized result shows that the velocity ratio, axial velocity spread and transverse velocity spread are 1.53, 7.10% and 3.39%, respectively.