GB690332A - Improvements in and relating to cathode-ray tubes comprising ion trap arrangements - Google Patents

Abstract

690,332. Cathode-ray tubes. MULLARD RADIO VALVE CO., Ltd., JONES, T. H., and TYRRELL, A. J. July 7, 1950 [July 13, 1949], No. 18498/49. Drawings to Specification. Class 39(i) A cathode-ray tube has an ion trap employing one or more permanent magnets arranged inside the envelope of the tube in proximity to the electron beam to render the latter emerging from an inclined gun coaxial with the tube. The magnet(s) may be supported from the gun or by mica insulating spacers. Adjustment of the magnetic field may be made by magnetising or demagnetising the magnet(s) when in position in the tube, or by a magnetic shunt outside the tube, or magnets of high coercive force premagnetised before fitting in the tube may be used together with auxiliary magnets easily magnetised or demagnetised from outside the tube producing only a small field. The premagnetised and auxiliary magnets may be on opposite sides of the beam and operate at different points and pole-pieces, not touching the magnets, may be used to direct the beam. The magnetic materials require to be degassed or may all be sealed in a separate envelope inside the tube and may be surrounded by a non-magnetic conducting screen to avoid heating of the magnetic material during eddy-current heating of the gun. Specifications 440,560 and 522,731, [Group II], referred to.