Charged particle apparatus with improved vacuum chamber

An apparatus, comprising:

• a vacuum chamber;
• an emission source located inside the vacuum chamber and configured to emit charged particles;
• a first aperture plate comprising a first plurality of holes, the first aperture plate being configured to block a portion of the emitted charged particles and pass the remaining emitted charged particles as a plurality of charged particle beamlets;
• a second aperture plate comprising a second plurality of holes and configured to pass the plurality of charged particle beamlets without blocking further charged particles;
• and
• an outgassing source;
• wherein the second aperture plate is configured to reduce passage of gas molecules from the outgassing source to the emission source.