A method for operating a charged particle beam emitting device and, in particular, an electron beam emitting device including a cold field emitter is provided. The method includes the steps of placing the cold field emitter in a vacuum of a given pressure, the emitter exhibiting a high initial emission current I0 and a lower stable mean emission current IS under a given electric extraction field; applying the given electric extraction field to the emitter for emitting electrons from the emitter surface; performing a cleaning process by applying at least one heating pulse to the cold field emitter for heating the emitter surface, whereby the cleaning process is performed before the emission current of the cold field emitter has declined to the lower stable mean emission value IS; and repeating the cleaning process to keep the emission current of the emitter continuously above the substantially stable emission value IS.