GB795090A - Improvements in or relating to travelling wave tubes with crossed electric and magnetic fields - Google Patents

Abstract

795,090. Travelling wave tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. July 3, 1956 [July 25, 1955], No. 20642/56. Class 39(1). In a travelling wave tube designed for crossed electric and magnetic fields the negative electrode 1, Figs. 1, 2, parallel to or concentric with the delay line is formed of resistive material with a loss angle of 45 degrees in the operating band and is connected to a biasing battery by a connection extending along its entire length so as to maintain its entire surface equipotential despite being struck by electrons from the beam. This impingement would normally cause generation of noise in the circuit connected to the negative electrode, particularly in high power tubes. As shown, the negative electrode 1 is carried in a peripheral groove in a metal support 2 supported by a metal disc 13 secured to three insulating rods 14, and its thickness is equal to or several times the skin depth. The resistivity of negative electrode 1 may be 50-1000 ohm.-cm, and the noise in the circuit to 1 due to electrons striking 1 is a minimum when p = 9À10#/E.W., where p = resistivity of material, e = dielectric constant, w = 2nf, the loss angle being 45 degrees. For h = 10 cm., p = 50 ohm.-cm. the skin depth is 6À5 mm. Collector 9 and screen 10 for decoupling the input 5 and output 6 may be integral, as shown, and the focusing electrode 8, which is positive to the cathode 7, is secured to the envelope by insulating supports 16. The invention can be applied to other types of travelling wave tubes of the crossed electric and magnetic field type, such as forward or backward wave amplifiers or oscillators of circular or linear type.