Patent GB-686830-A (GB)
Title: Improvements in or relating to electron discharge apparatus
Inventor: BECK ARNOLD HUGH WILLIAM
IPC: H01J25/12
Filed: 1949-06-08
Abstract: 686,830. High-frequency discharge apparatus. STANDARD TELEPHONES & CABLES, Ltd. June 8, 1949, No. 15259/49. Class 39(i) Apparatus of the kind in which a plurality of electron discharge devices are distributed at half wavelength intervals along and afford coupling between a pair of transmission lines, is characterized in that the said transmission lines are lengths of hollow rectangular waveguide abutting one against the other, preferably with a common wall, and that each said discharge device is similarly orientated with respect to the waveguides and is arranged to project a beam of electrons from one side of one of the said waveguides across the guide through a buncher gap therein and across the other waveguide through a catcher gap therein, the two said gaps being separated by a drift tube passing through the abutting walls or the said common wall, respectively. The oscillator shown comprises two sections 1 and 6 of rectangular waveguide. Section 1 is closed at one end by a sheet of copper 2 forming a reflecting termination and at the other end by a window 3 communicating with a further portion of waveguide 4 which is provided with a tuning piston 5. Two electron guns mounted in cups 18 secured to the wall of the waveguide and closed by glass presses 19, one of which carries an exhaust tubulation (not shown), are spaced half a wavelength apart. Waveguide section 6 is coupled at one end by a window 3 to a tuning section 4 provided with a tuning piston 5 and at the other end by a window 7 to an output waveguide 8. The window 7 is designed to match the apparatus to the load by, for example, making it the same as the windows 3 and clamping a thin matching diaphragm over it. Drift tubes 9 project through the dividing wall 10 and form gaps with projections 14 and 14<SP>1</SP> on the outer walls. The upper projections 14<SP>1</SP> may be omitted, in which case the upper wall forms a collector for the electron beam, or separate collector electrodes 15 are provided. insulated by glass collars 16 from metal collars 17 mounted on the wall. The electron guns may use either circular beams or beams of rectangular cross-section, in which case the drift tubes 9 collars 16 and cups 18 are of oval cross-section. A slot 22 in wall 10 provides a feedback path between the output and input sections of the oscillator, and diaphragm 27, which may be of lossy material or may be made resistive by painting on a suitable colloidal graphite preparation, are provided to suppress any tendency to oscillate at one half the desired wavelength. For use as an amplifier, the reflecting termination 2 is replaced by an input waveguide which may be similar to the output waveguide 8 and coupled by means of a matching window similar to 7, the coupling slot 22 and diaphragms 27 being omitted. A " transparent " amplifier, i.e. one whose input and output impedances are matched to the input and output waveguides, respectively, is obtained by omitting the tuning pistons 5 and replacing them with matching terminations. The waveguide sections 1 and 6 are secured to the tuning sections 4 and 41 and to the output guide 8 by means of flanges 25 and 26 bolted together, so that additional two beam units can easily be added. Each unit is basically in the form of a rectangular box made of steel or one of the special alloys which readily seal to glass. The dividing wall 10, flanges 25, drift tubes 9, projections 14 and 14<SP>1</SP> collars 17 and cups 18 are secured weakly in position and copper wire placed round all the joints. The box is then raised to a temperature of from 1090‹ to 1100‹K in a reducing atmosphere so that the copper melts and brazes all the parts together. The box is then copper plated internally. Alternatively, all the parts may be copper plated initially and the copper made to flow to solder the parts together. The solder used to secure the metal frames of the windows 3 and 7 in position may be a copper-silver or copper-gold eutectic alloy.