An electron beam source for use in an electron gun. The electron beam source includes an emitter terminating in a tip. The emitter is configured to generate an electron beam. The electron beam source further includes a suppressor electrode laterally surrounding the emitter such that the tip of the emitter protrudes through the suppressor electrode and an extractor electrode disposed adjacent the tip of the emitter. The extractor electrode comprises a magnetic disk whose magnetic field is aligned with an axis of the electron beam.