Electrostatic lenses are ion-optical elements used to guide and focus charged particle beams without changing their kinetic energy.
The most prominent representative is an Einzel lens which consists of three cylindrical electrodes. Focusing of the beam is achieved by applying a high voltage to the central electrode.
Electrostatic lenses can be used in broad pressure ranges, down to ultra-high vacuum conditions.
Figure 1: Schematic view of a cylinder symmetrical Einzel lense configuration showing the ion path. Three cylindrical electrodes are parallel to the ion flight path with the center cylinder at a particular potential, in deceleration mode. (Exemplary sketch by Schnieri - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=58602669)