从理论上研究了“电子束电偏转实验”中亮斑的形成原因及其线度的影响因素，推导出电子流偏转总量x、亮斑线度Δ 的表达式，并进行了数值模拟.研究结果表明，亮斑是由射入偏转电场的锥形电子束( 其锥角Δθ 实为一很小的量) 引起，而造成Δ 随加速电压U1、偏转电压Ux变化的原因是由于Δθ 关于偏转电场中心轴( z 轴) 的不对称分布.Δ 的大小还取决于Δθ 的大小.

In the electric deflection of electron beam，the causes of bright spots and the factors of spots length are studied theoretically. The total expression x，of electron flow deflection and the length Δ，of bright spots are obtained and simulated numerically. The results show that bright spots are caused by the conical electron beam introduced into deflection field ( the angle Δθ，of conical electron beam is very small) ，and the reason of Δ varying with the change of accelerating voltage U1 ，deflection voltage Ux is Δθ asymmetry distribution on the central axis of deflection field. Also，Δ depends on the value of Δθ.