An arrangement of two conducting sheets forming a capactor and giving a radial electrostatic field which is used to deflect and focus ion beams of different energies. The capacitor may, for example, be cylindrical, spherical or toroidal.
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1544 (https://doi.org/10.1351/pac199163101541)