GB795803A - Improvements relating to electron discharge devices having ion trap arrangements - Google Patents

Abstract

795,803. Ion trapping in cathode ray tube. ELECTRIC & MUSICAL INDUSTRIES, Ltd. March 28, 1955 [April 9, 1954], No. 10439/54. Class 39(1). An ion trap gun comprises an electrode 7, Fig. 1 with an eccentric aperture arranged between the first and second anodes 4, 5, the arrangement being such that the electrostatic fields between 4, 7 and 5, 7 have transverse components to deflect the beam twice in the same direction, the electrons subsequently being deflected back by means of a magnetic field. By keeping the electrostatic ion trap deflections small it is stated that distortion of the beam cross section can be minimized. The potential of electrode 7 must be less than that of second anode 5 ; it is stated that the potentials of 4, 7 can be equal in which case they can be joined by a tubular member or formed as an integral structure, Fig. 2 (not shown). The beam outlet end of second anode 5 may or may not have a transverse wall 6. The ion trap magnetic field is produced by a permanent magnet held on the tube neck by a spring clip in the correct angular and axial position and magnetic focusing is achieved by an annular permanent magnet or electromagnet. Since a single ion trap magnet cannot centre the beam on the tube axis if the gun and tube axis coincide, the gun axis may be tilted with respect to the tube axis. The second anode 5 need not be the final anode but can form the first electrode of a two electrode or unipotential electrostatic lens ; in this case electrode 5 has a transverse wall between its ends to prevent negative ions or secondary electrons from reaching the lens field.