Patent GB-706909-A (GB)
Title: Improvements in or relating to electrical amplifying devices of the travelling wave kind
IPC: H01J25/36
Filed: 1950-07-27
Abstract: 706,909. Magnetron amplifiers. M-O VALVE CO., Ltd., and CLARKE, G. M. Oct. 5, 1951 [July 27, 1950], No. 18847/50. Class 39(1) [Also in Group XL(b)] A travelling wave magnetron amplifier comprises two concentric cylindrical conductors between which a radial electric field is maintained and means are provided for setting up a circular magnetic field transverse to the radial electric field, and at least one of the conductors carries one or more helical partitions to form a coiled waveguide structure, one or more cathodes are arranged adjacent to the aligned slots between one conductor and a partition or partitions of the other conductor or between two partitions carried by the respective conductors and the structure is coupled to input and output circuits by straight sections of guide forming an integral part of the tube structure. In one form, Fig. 1, the inner conductor 1 is supported and spaced from the outer conductor 2 at each end by a glass annulus 3 sealed between flanges 4, 5 on the conductors. The conductor 2 carries a single helical partition 6 and the inner conductor is formed as an indirectly heated cathode, Fig. 2 (not shown). Input and output guide sections 9, 10 are soldered to apertures in the outer conductor, which serves as the evacuated envelope, and hermetically closed by glass windows 11, 12; 13 is a metal evacuation tube closed by cold-welding, or a glass tube may be used. The input wave may be of H 10  mode, 2 is kept positive with respect to I, and a unidirectional current is passed through 1 to set up a circular magnetic field and axial voltage gradient. The combination of the electric and magnetic fields gives the electrons an axial velocity which is correlated with the axial component of the wave velocity. The cathode is heated to emission temperature partly by the current through 1 and partly by the current through the heater (not shown). The axial voltage gradient is however not an essential feature. In a modification, Fig. 3 (not shown) the helical partition is secured to the inner conductor which is at higher D.C. positive potential than the outer conductor. A unidirectional current is passed through the inner conductor to generate the circular magnetic field and axial voltage gradient, and the outer conductor has an emissive coating and is heated by a coiled coil arrangement having as small a resultant magnetic field as possible. The inner conductor and helical partition may be formed in one piece by cutting a helical groove in a solid rod. In further modifications, the electron emission may be localized to a small region of the cathode, or a plurality of spaced cathodes may be used. A plurality of partitions may be used, and the turns of the helical guide may be spaced apart. Both conductors may be provided with one or more partitions but this is not preferred. The radial electrostatic field may be applied in pulses in which case the current setting up the magnetic field is pulsed synchronously; by varying the duration of the current pulses the cathode heating can be controlled.