| 摘要 |
752,452. Velocity-modulated tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. March 15, 1954 [March 24, 1953], No. 8013/53. Class 39 (1). In an electron discharge device having a hollow elongated electron collecting electrode, a barrier is provided within and extending across said electrode away from the open end thereof and is arranged so as to allow electrons to pass into said electrode but substantially prevents electrons or charged particles from escaping therefrom. The structure shown is part of a high-power klystron and comprises a drift tube 1 and resonator 2 through which an electron beam is projected into a hollow collecting electrode 4 of stepped construction which is cooled in operation by the circulation of fluid or forced air over its external surface. The electrode 4 is made of copper or iron which readily acquire an oxidized surface which is bombarded by electrons so that secondary electrons and charged particles such as positive ions are released. In the normal course of events these secondary electrons and charged particles would return through the resonator 2 to form an additional beam loading which would reduce the efficiency of the device, while the positive ions would bombard the cathode, resulting in poisoning in the case of an oxide cathode. According to the invention a barrier comprising four structures, Fig. 2, each in the form of a grid having a series of slats 7 arranged across a circular frame 8 is secured to the annular steps 6 along the wall of the electrode 4 to collect the secondary electrons and charged particles. The barrier structures are arranged so that the slats 7 in successive structures assume different angular positions relatively to the axis of the electrode 4. The secondary electrons and charged particles travel mainly in a direction towards the axis of the electrode 4 and will thus in all probability strike one of the slats 7 and be collected thereby. The open end of the electrode 4 is made conical in shape to collect any secondary electrons produced by electrons of the beam striking the edges of the slats 7 of the first barrier structure. A more efficient arrangement whereby the charged particles are fixed or absorbed as by a gettering action may be achieved if the slats 7 are either formed of or coated with a getter material such as zirconium, thorium, tantalum, molybdenum or hafnium. By suitably selecting the surface area of each slat 7 it may be arranged that the centre of the slat attains a temperature of about 1000‹ C. under the primary electron bombardment, at which temperature the getter materials are most efficient. Since positive ions are prevented from returning to the cathode, an oxide-coated cathode may be employed in the high-power device. A barrier of the kind described may be employed in the collecting electrode of a travelling-wave tube. |
