GB856123A - Vacuum-tubes - Google Patents

Abstract

856,123. Discharge tubes. MULLARD Ltd. Feb. 9, 1959, No. 4444/59. Class 39(1). An electron beam tube comprises a single vacuum-tight envelope within which are disposed an electron-beam device, an ion pump assembly and means for forming a film of getter metal on a surface inside the envelope and adjacent the ion pump assembly. In the tube shown, the electron-beam device is a backward-wave oscillator comprising a cathode K, cathode electrode C and anode A forming an electron beam which passes along a slow-wave structure D such as an interdigital line to a collector electrode X. The output is taken through a matching section M such as a fin-line structure to a window W which is formed in a metal end-cap L and may be as described in Specification 787,925 [Group XL(b)]. The ion pump comprises a filament F and auxiliary filament S surrounded by a helical grid G. The auxiliary filament S consists of a wire of getter metal such as titanium or zirconium wound around a heating wire. Shielding discs B confine the deposition of vaporized getter metal to the region of the envelope adjacent the ion pump assembly. The filament F may be dispensed with and the heating wire utilized also to produce ionizing electrons. The getter film may be produced by any other method. The ion pump maintains a low pressure in the envelope and prevents undesirable noise modulation in the backward-wave oscillator by ionized residual gas. The invention is applicable to any electron-beam device.