The utilization of positive ions for investigations of stray field effects in electrostatic lenses

The paper describes a method for the investigation of stray fields caused by surface charges on the glass supports of cathode-ray-tube guns. These stray fields may penetrate into the gap of an unshielded electrostatic lens and contribute to the astigmatic distortions of the entire electron optical system. The focused spot on the screen of the tube then shows deviations from the ideal circular shape. The investigation of the stray field influences was carried out utilizing the positive ion component of the electron beam. Discoloration patterns on the second grid aperture due to ion bombardment indicated the expected distortion of the focused spot. Various gun designs were tested in this manner.