| 摘要 |
767,446. Thermionic cathode tubes. WESTERN ELECTRIC CO., Inc. May 28, 1954 [June 15, 1953; June 15, 1953; June 15, 1953], No. 15854/54. Class 39(1). An indirectly heated hollow cathode with an interior coating of emissive material has at least one aperture for the egress of electrons, the dimensions of the aperture being such and so correlated that the emergent beam has a predetermined cross-section and density, and a perveance of at least 10 x 10<-6> amps/volt<3>/2. The interior may be a closed cylinder, Fig. 2, with a circular aperture 14 of diameter D and length L, Fig. 3. A solid or hollow beam is obtained according to whether D/L is < 1 OR > 1. The cathode may be usefully operated at 700‹C., i.e. about 100‹ below the normal temperature for oxide-coated cathodes, and has high emission and high perveance under low accelerating voltages. The aperture may be frustoconical outwards or inwards, Figs. 5 and 6 (not shown), to control collimation, or convergence or divergence, of the beam. The aperture may be rectangular, Fig. 7 (not shown) and Fig. 8, producing a rectangular beam, which may be solid or hollow as B/L is <1 OR > 1. If the coating is a strip only, of less length than the length A of the aperture, as shown in Fig. 8, the condition B/L> 1 gives two planar sheets of electrons. Fig. 9 has an internal screen 30 which acts as a conventional control grid. In Fig. 10 (not shown), an internal pointed rod acts as a control or accelerating electrode. The hollow may be spherical, Fig. 11 (not shown), and may have more than one aperture, 114, 124, Fig. 14, each with its corresponding anode 111, 121. Fig. 16 has a toroidal hollow 152, with an annular orifice 154. In this arrangement, since no portion of the emissive coating directly faces the anode 157, the coating is shielded from positive ions and other particles from the anode. Fig. 18 shows another form of toroidal cavity 171, with an annular orifice 173. Under the condition for hollow beams, this arrangement produces two coaxial hollow beams, which may be of advantage for dual stream travelling wave tubes. The spherical cavity types may also have an internal control or accelerating electrode, Figs. 19 and 20 (not shown). If this electrode is of the pointed rod form, it may have a secondary emissive coating. A cathode may have several apertures, each with its corresponding separate anode which can be independently controlled to vary the current in one beam without affecting the adjacent beams. Similarly independent modulating electrodes may also be provided. Fig. 25 has a single anode 255 receiving electrons from the cathode 251 through several apertures. The cathode may be hemispherical, Fig. 26, to combine the advantages of a large internal surface and uniform anode-cathode spacing. The control electrode may be a mesh, or a plate with apertures corresponding to the cathode apertures. |
