Patent ID: 6828565
Filing Date: 2004-12-07
Classification: H01J

Abstract:
An electron beam source for generating a beam of electrons, the electron beam source comprising:a cathode body having a source surface for emission of electrons; an anode disposed at a distance from the cathode body, for generating an extraction field for extracting the electrons from the source surface; a heater for heating the cathode body; a photon source for generating at least one photon beam directed onto the source surface for assisting in the electron emission, wherein the photon source is configured such that an intensity of the at least one photon beam is adjustable; a detector for detecting a beam current of the electron beam and for providing a measuring signal representing the electron beam current; and a controller configured to control the intensity of the photon beam based on the measuring signal in a normal mode of operation of the electron beam source, wherein, in a mode of operation different from the normal mode of operation and in which the photon beam is not directed onto the source surface, the electron beam current is higher than about 0.3 times the electron beam current in the normal mode of operation.