A charged-particle source configured for emission of electrically charged particles, in particular electrons, as a charged-particle beam along a direction of emission (e), said charged-particle source comprising - a housing connectable to a vacuum system, allowing the charged-particle source being operated at a high vacuum, - an emitter electrode, having an emitter surface configured to emit charged particles of a specific particle species along the direction of emission, - a counter electrode configured to being applied an electrostatic voltage with respect to the emitter electrode at a sign opposite to that of the electrically charged particles, the counter electrode having an emitter aperture at a location downstream of the emitter surface along said direction of emission, - a source space defined between the emitter surface and the emitter aperture, - at least two adjustment electrodes (106, 107, 108, 109), located surrounding the source space between the emitter electrode and the counter electrode, each adjustment electrode being configured to being applied a controlled electrostatic voltage with respect to the counter and/or emitter electrodes, and - a pressure regulator device, said pressure regulator device being configured to control the pressure of gas present in the source space, the particle source being operable in an emission mode wherein a voltage is applied between the emitter and counter electrodes (101, 103), causing generation of charged particles leaving the particle source along the direction of emission (e), the particle source being further operable in a first cleaning mode wherein - a gas is held at a pre-defined pressure value within the source space, while applying a voltage between the emitter and counter electrodes (101, 103), wherein secondary electrons generated by charged particles at the counter electrode ionize particles of said gas in the source space, producing ionized gas particles, and - electrostatic potentials are applied to at least some of the adjustment electrodes, generating an electric field directing said ionized gas particles onto the emitter surface. - a housing connectable to a vacuum system, allowing the charged-particle source being operated at a high vacuum, - an emitter electrode, having an emitter surface configured to emit charged particles of a specific particle species along the direction of emission, - a counter electrode configured to being applied an electrostatic voltage with respect to the emitter electrode at a sign opposite to that of the electrically charged particles, the counter electrode having an emitter aperture at a location downstream of the emitter surface along said direction of emission, - a source space defined between the emitter surface and the emitter aperture, - at least two adjustment electrodes (106, 107, 108, 109), located surrounding the source space between the emitter electrode and the counter electrode, each adjustment electrode being configured to being applied a controlled electrostatic voltage with respect to the counter and/or emitter electrodes, and - a pressure regulator device, said pressure regulator device being configured to control the pressure of gas present in the source space, the particle source being operable in an emission mode wherein a voltage is applied between the emitter and counter electrodes (101, 103), causing generation of charged particles leaving the particle source along the direction of emission (e), the particle source being further operable in a first cleaning mode wherein - a gas is held at a pre-defined pressure value within the source space, while applying a voltage between the emitter and counter electrodes (101, 103), wherein secondary electrons generated by charged particles at the counter electrode ionize particles of said gas in the source space, producing ionized gas particles, and - electrostatic potentials are applied to at least some of the adjustment electrodes, generating an electric field directing said ionized gas particles onto the emitter surface. - a gas is held at a pre-defined pressure value within the source space, while applying a voltage between the emitter and counter electrodes (101, 103), wherein secondary electrons generated by charged particles at the counter electrode ionize particles of said gas in the source space, producing ionized gas particles, and - electrostatic potentials are applied to at least some of the adjustment electrodes, generating an electric field directing said ionized gas particles onto the emitter surface.