Fringe field effects on electrostatic deflection of electrons by a pair of charged plates

Electrostatic deflection of electrons by a pair of charged metal plates was studied over a range of electron kinetic energies. This was achieved using an electron gun in a cathode-ray tube assembly powered by a variable high-voltage controller. A deflection voltage was applied across charged symmetrical metal plates to deflect an electron beam vertically, and tracked on the phosphor screen of the cathode-ray tube. The deflection plates were shaped to allow maximum deflection: the beginning half of each was parallel, while the end portion was tapered. Our experimental results confirmed a universal scaling relationship between the electron deflection, as measured by the deflection tangent, and the voltage ratio of deflection versus acceleration, within 2% uncertainty over the range of accelerating voltage between 248 V and 527 V. A proper geometric ratio of plate length over its separation was 3.41 which by conventional analysis without considering the fringe field, served as a scaling factor for beam deflection versus the voltage ratio of deflection and accelerating biases. Our study demonstrated that fringe fields contribute considerably to the electron beam deflection, both prior to and after it going through the charged region. By considering the effects of the fringe fields, our model analysis revealed that fringe fields contribute up to 20% of the electron deflection, accounting for experimental results within 2%.