Trajectory displacement of a single electron in the drift tube

The positive charge distribution, which is electro-statically induced by a single electron over the inner wall of a drift tube with a constant radius, is analytically calculated. The potential by it is calculated analytically also. The trajectory displacement at image plane of an objective lens, that is, the charge-induced aberration is estimated for two simple lens-models, approximating them electro-statically by a constant radius drift tube. It seems to be less than the diffraction aberration, when the accelerating voltage is higher than 100 V.