GB424822A - Improvements in or relating to x-ray tubes having an anode adapted to move when in use - Google Patents

Abstract

424,822. R÷ntgen-ray tubes. MULLER AKT.-GES., C. H. F., 24, R÷ntgenstrasse, Hamburg, Germany. Sept. 28, 1934, No. 27849. Convention date, Sept. 30, 1933. [Class 39 (i)] In an X-ray tube having an anode moving relatively to the electron beam, the electron density in the beam is non-uniform so that the specific load on the focal spot decreases in the direction of movement of the anode. The anode 1, Fig. 1, moves in the direction of the arrow and the electron density of the beam from the helical cathode 2 decreases from left to right. Each point of the anode surface is heavily loaded when it first enters the focal spot and its temperature is raised to the maximum permissible temperature more rapidly than would be the case if the electron beam were uniform. The total load is thus increased without overheating the anode. The non- uniform emission may be produced by non- uniform cathode temperatures, the left-hand side of the coils of the filament 2 being kept at a higher temperature than the right-hand side by making the left-hand side 4 of the recess in the focusing device 3 a better heat reflector than the right hand side, which may be spaced away from the filament 2 as shown. In a modification (Fig. 2, not shown), the recess in the focusing device is symmetrical and the non-uniform temperatures are produced by etching or otherwise reducing the diameter of the filament at the left-hand side, the filament being an oval helix or being bent to and fro in loops. In further modifications, (Figs. 3 and 4, not shown), the cathode consists of parallel filaments of different resistance, for example, of the same material and different diameters, the temperature of the thickest filament being the greatest if the filaments are connected in parallel and the least if they are connected in series. In another modification, (Fig. 5, not shown), the non-uniform electron beam is produced by a grid of non-uniform mesh in front of the cathode and at the cathode or a slightly lower potential. The non-uniform beam may also be produced by increasing the emission surface at the left-hand side. A helical or looped filament, Fig. 6, has additional small loops 13, or a small helix is arranged eccentrically in a larger helix, (Figs. 7 and 8, not shown). In a further modification, an additional filament 19, Fig. 9, screened from the anode 1, heats the left-hand side of the filament 18 and also adds its emission to the left-hand part of the beam. The anode may be rotated by a magnetic stator external to the tube, or may be moved with the tube whilst keeping the cathode stationary, or the electron beam may be deflected electrically or magnetically and the anode moved relatively thereto.