GB654588A - Improvements in apparatus for separating particles of different charge-to-mass ratio - Google Patents

Abstract

654,588. Discharge apparatus. SYLVANIA ELECTRIC PRODUCTS, Inc. Feb. 27, 1948, No. 6186. Convention date, Nov. 30, 1946. [Class 39 (i)] In apparatus, such as a cathode-ray tube or a mass spectrometer, having crossed magnetic and electrostatic fields for separating particles of a given ratio of charge to mass from a beam of charged particles, the pairs of elements producing the fields are so shaped that, when energized in predetermined proportion, the deflecting effects of the two fields on the selected particles are mutually cancelled at every point on the beam axis. In the preferred form, a cathode-ray tube is provided with gun 14, fluorescent screen 24 and an ion trap comprising magnet 26 and deflecting plates 34, whereby ions are deflected out of the electron beam to impinge on the disc 25. The plates are connected to potentiometer 42, the mid-point of which is connected to the coating 12 of material, known under the Registered Trade Mark " Aquadag," which ensures a uniform electrostatic field in the vicinity of the trap. Local deflections of the beam within the trap with consequent beam distortion are eliminated by shaping the plates, e.g. as shown, to conform as near as possible with the magnetic lines of force generated by rectangular polepieces; alternatively, the shape of the plates may first be determined and the polepieces subsequently designed. The electrostatic fields may be computed by immersing the plates, connected to a suitable potential, in an electrolyte. Specifications 505,632 and 538,684 are referred to.