Patent ID: 7595490

Claim:
A method for operating a charged particle beam emitting device comprising a charged particle beam source having an emitter surface, the method comprising the steps of: (a) placing the charged particle beam source in a vacuum of a given pressure, the charged particle beam source exhibiting a high initial emission current I 0 and a lower stable mean emission current I S under given operational conditions; (b) applying the given operational conditions to the charged particle beam source for emitting charged particles from the emitter surface, so that the emission current of the charged particle beam source is higher than the stable mean emission current I S ; (c) performing a cleaning process by applying at least one heating pulse to the charged particle beam source for heating the emitter surface to a temperature T C , whereby the cleaning process is performed before the emission current of the charged particle beam source has declined to the lower stable mean emission value I S ; and (d) repeating the cleaning process to keep the emission current of the charged particle beam source continuously above the substantially stable emission value I S .