Patent GB-942685-A (GB)
Title: High power electron discharge device
IPC: H01J25/42
Filed: 1961-03-20
Abstract: 942,685. Magnetrons. S.F.D. LABORATORIES Inc. March 20, 1961 [March 21, 1960], No. 10141/61. Heading H1D. An electron discharge device using crossed electric and magnetic fields for wave-electron stream interaction comprises an anode structure 21, Figs. 2, 3A, a cathode structure 23 spaced from the anode structure to form a wave-electron interaction space therebetween, and means for producing an electron stream in the interaction region, the anode being adapted to propagate an electromagnetic wave travelling in a direction substantially orthogonal to the mean direction of the electron stream, whereby energy is transferred from the electron stream to the travelling electromagnetic wave propagated by the anode over an interaction region longer than a wavelength of the dominant mode propagated by the anode structure. In one embodiment of the invention, Fig. 2, a coaxial, inside-out magnetron comprises a thick-walled hollow cylindrical anode 21 which forms a circular electric mode waveguide 22, e.g. a TE 01  mode waveguide. A hollow cylindrical cathode 23, a cold cathode of beryllium copper, surrounds and is spaced from the anode 21, the emission from which is initiated by the R.F. wave in the device. The anode structure 21 is ¥# thick, where # is the cut-off wavelength of the waveguide 22 and is provided with a plurality of resonator slots 25, Fig. 3A, which subdivide the anode into a plurality of anode members 26, each provided with a slot resonator 27 #/ 4  deep extending practically the whole length thereof. In operation, a # mode interaction takes place and a phase reversal between adjacent slots is maintained by having adjacent slots differing in length by an odd multiple of #/4. In a further embodiment, Fig. 4, the #/ 4  slot resonators 27 of Fig. 3A are replaced by <SP>5</SP>#/4 slot resonators 38 which are foreshortened by loading the inductive and capacitive portions so that it occupies the same length as the <SP>3</SP>#/4 slot resonator 25. Alternatively, Fig. 4A (not shown), #/4 slot resonators may communicate with the waveguide by reducing the inductive portion compared with the capacitive portion Mode control means may be provided in the form of dielectric rods or tubes 41, Fig. 5 (not shown), positioned within the device at the openings of slot resonators 25 into the waveguide 22 where voltage nulls occur for the desired mode, these may be covered with lossy material such as carbon or may have water flowing through them at high power levels; alternatively, axial modes may be effectively damped by cutting circular or helical grooves 42, Fig. 6, #/4 deep on the inside of anode walls 43 and filling these with lossy material or with continuous bands of lossy material such as carbonized ceramic 40, Fig. 6A (not shown). To enhance the R.F. field at the cathode, resonant slots may be cut into its interior surface opposite the anode slots 25, or a slow wave structure 47, Fig. 9, may be provided on the cathode which is identical with that, 48, on the anode. To control the operation of the device at low power levels, a plurality of thermionic strip cathodes may be positioned in axially aligned grooves in the cold cathode and set back from the surface of the cathode, Fig. 11 (not shown). Fig. 13 shows helical grooves 58 #/ 4  deep cut in the inside surface of the cathode 59; the direction in which these grooves spiral is selected to be opposed to the spiral of the helical contours of the electron " spokes " synchronous velocity and the R.F. wave, thus attenuating reflected waves travelling on the anode. In all cases a solenoid surrounds the structure to provide an axial magnetic field, and cooling channels, e.g. 28, Fig. 3A, provided in the anode portions for the circulation of water.