A multi-beam particle microscope with a micro-optical unit for generating the multiplicity of individual beams is disclosed. The micro-optical unit comprises a mechanism for setting and maintaining an unchanging imaging property of the multiplicity of individual beams. In one example, the micro-optical unit comprises at least one measuring apparatus used to sense a change in length, a change in distance, a contamination or degradation of a component of the micro-optical unit during operation. A multi-beam particle microscope comprises a control unit which establishes an effect on at least one individual beam from a change in length, a change in distance, a contamination or degradation of the component. A multi-beam particle microscope also comprises a compensation element for compensating the effect on the at least one individual beam. According to a method for operating a multi-beam particle microscope, a remaining service life of the multi-beam particle microscope which meets a demand with respect to a wafer inspection is also established.

A system and a method for an adaptive plasma-cleaning process for a reaction chamber allow continual monitoring by a residual gas analyzer, while active plasma-cleaning is carried out in the reaction chamber. The system includes a valve system and a pump system that allow the residual gas analyzer to perform continual monitoring at a favorable pressure condition that is independent of the active plasma-cleaning process.