Electron gun, electron beam applicator, and method for controlling electron gun

A method for controlling an electron gun that monitors an intensity change of an electron beam emitted from a semiconductor photocathode due to semiconductor photocathode degradation comprising:

• a light source,
• a semiconductor photocathode that emits an electron beam in response to receiving light from the light source,
• an anode,
• an electron-beam-shielding member with which it is possible to shield part of the electron beam,
• a measurement unit that measures the intensity change of the electron beam emitted from the semiconductor photocathode due to semiconductor photocathode degradation using a measurement electron beam shielded by the electron-beam-shielding member, and
• a control unit that adjusts the intensity of the electron beam emitted from the semiconductor photocathode in accordance with results of measurement performed by the measurement unit,
• wherein the method for controlling an electron gun comprises:
• a step for irradiating the semiconductor photocathode with excitation light from the light source, and emitting an electron beam from the semiconductor photocathode in response to receiving the excitation light;
• a step for measuring the intensity of the electron beam using the measurement electron beam shielded by the electron-beam-shielding member, and
• a step for adjusting the intensity of the electron beam emitted from the semiconductor photocathode in accordance with the intensity of the electron beam measured in the step for measuring the intensity of the electron beam;
• wherein the electron beam is formed by electrons in which electrons within the semiconductor photocathode are excited by the excitation light emitted from the light source, and the excited electrons are emitted from the semiconductor photocathode, and
• the control unit controls the light source to vary the intensity of the excitation light with which the semiconductor photocathode is irradiated either when a measurement value falls below a preset threshold value or in a prescribed period of time on a basis of the measurement value, in order to adjust the intensity of the electron beam emitted from the semiconductor photocathode such that the semiconductor photocathode degradation is compensated.