Patent GB-1006063-A (GB)
Title: High voltage vacuum tube
IPC: H01J5/06
Filed: 1962-05-21
Abstract: 1,006,063. High voltage vacuum tubes. HIGH VOLTAGE ENGINEERING CORPORATION. May 21, 1962 [May 25, 1961], No. 19418/62. Heading H1D. An elongated high voltage vacuum tube comprises a longitudinal insulating passageway provided with electric field shaping means which make the lines of electric field strength incline with respect to the longitudinal axis of the passageway to such an extent that the longest line of electric field strength within the passageway is shorter than the length of the passageway. This arrangement reduces or eliminates the so-called " total voltage " effect, i.e. breakdown caused by secondary charged particles. As shown, an insulating tube 2<SP>1</SP>, Fig. 2, has a helical resistive, india ink line on its outer surface, the turns of the helix being squeezed to the left at one side of the tube, and to the right at the opposite side, so that a potential difference applied between wedge-shaped, conductive end layers 7, 8 results in an electric field E inclined to the tube axis. These secondary particles produced by ionization of a gas molecule can only be accelerated to a fraction of the total applied voltage. In Fig. 3, the tube comprises wedge-shaped metal end flanges and insulating rings 10 having metal coatings 11 bonded together with an epoxy resin. The coatings 11 lie in parallel planes, which are not perpendicular to the tube axis, and extend into grooves 16 containing metal terminal rings 15. The metal-coated insulating rings 10 may be replaced by conductive glass rings, terminal rings 15 being provided to ensure an inclined electric field E. Alternatively, the tube may comprise insulating rings 10 separated by apertured electrode discs which may be planar or are bent to increase the angle of inclination of the field E, Fig. 8 (not shown). These tubes may be used as differential pumping tubes or neutral beam tubes. In an acceleration tube according to the invention, the electric field is inclined to the trajectory of the particles being accelerated. In Fig. 9, electrode discs 25-29, having elongated apertures, include sets which are tilted alternately in opposite directions, so that particles in the primary beam are accelerated along the tube axis, while secondary particles, which are created with negligible velocity, will be trapped. The electrode discs may be dished to provide shielding of insulating rings 24. The primary beam may be injected at an energy of 1 Mev. from a known acceleration tube provided with magnets, Fig. 12 (not shown). Alternatively, a beam may be injected from one side of, and/or at an angle to, the tube axis from a conventional electron gun, or from a cathode filament, mounted in a field free region, Figs. 14-17 (not shown). Also, electrons may commence their trajectory in a curved field to avoid ion bombardment of the filament. The tandem accelerator shown in Fig. 18 comprises three high voltage tubes 102-104 connected to a resistive path 109, 110 between electrode 100, charged to 6 million volts from belt 101, and ground. The high voltage generator and tubes are mounted in a tank which contains insulating gas under pressure, or is evacuated. In the latter case the tubes 102-104 need not be vacuum-tight. Tube 104 is a differential pumping tube, and negative ions from source 105 are accelerated by tube 102 to a stripper electrode 106 having a canal 107 to which gas is admitted so that positive ions are formed, and are accelerated through tube 103. Tube 102 may include a conventional beam-deflecting device adjacent ion source 105, and may also contain within flanged cylinder 111, a beam steering device as described in Specification 1,006,064, for directing the beam into canal 107.