GB781205A - Improvements in travelling wave tubes - Google Patents

Abstract

781,205. Travelling-wave tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. March 4, 1955 [March 4, 1954], No. 6521/55. Class 39(1). In a high power travelling-wave tube of the magnetron type, the negative electrode 27, Fig. 1, has a part 2 near the cathode which is highly secondary electron emissive and a part 3 near the collector which absorbs primary electrons and is prevented from emitting secondary electrons. Preferably part 2 is five times as long as part 3. The cathode and collector ends of the system may be curved, Figs. 9, 10. The negative electrode may be divided into an element 320, Fig. 11, with the cathode 301 and a secondary electron emissive part 310, an element 302 with a secondary electron emissive part 310<SP>1</SP> and an element 303 which absorbs secondary electrons. A relatively weak field between element 303 and collector 9 helps to prevent the escape of secondary electrons. The end of element 302 next to element 303 may also absorb secondary electrons. Element 303 may be subdivided into several parts at successively higher potentials. Element 303 may be wholly within the interaction space and nearer the delay line 305. In Fig. 12, element 421 is plane and element 422 has the secondary electron emissive and absorbent parts 410<SP>1</SP>, 403. The delay line has an attenuating zone 8, Figs. 1 and 10, or 308, Figs. 11 and 12. The tube may be of the backward-wave type with a circular structure. The highly secondary electron emissive parts may include a layer of a metal such as platinum deposited electrolytically, or of an alloy such as copper beryllium. Alkaline oxides may be deposited on a surface treated mechanically or chemically to form a rough or porous surface ; e.g. molten metal may be sprayed on the surface. The secondary electron absorbing parts may include parallel longitudinal grooves in the direction of the beam. Similar grooves may be provided at the sides of the secondary electron emissive parts.