GB616816A - Improvements in or relating to velocity-modulated discharge tubes - Google Patents

Abstract

616,816. Velocity-modulated tubes. PHILIPS LAMPS, Ltd. March 9, 1946, No. 7440. Convention date, June 25, 1941. [Class 39 (i)] An electron beam, velocity-modulated in control system 5, 6, 7, Fig. 1, passes to a brake field electrode 10 which is perforated and is held at such a potential that the slower electrons are reflected back into the control system, while becoming bunched, so as to reduce the effective damping of the resonant circuit 8 connected to this circuit, while the faster ones pass on through the aperture and give up their energy to an output circuit 12 connected between the electrode 10 and a collector electrode 11. The reflected electrons are again reflected near the cathode by reflector 4, and these electrons thus oscillate to and fro, giving up energy to the control system each time, the transit time from the centre of electrode 5 to either reflector and back being for this purpose chosen to be one or more periods of the control oscillation. Magnetic focussing by a coil or a permanent magnet is employed to prevent electrons straying from the beam before they have made a sufficient number of transits. The transit time between electrodes 10 and 11 for optimum energy transfer by the faster electrons is one or an odd multiple of a halfperiod of the oscillation. The circuits 8, 12 may be coupled inductively-or the same circuit may serve both functions. In a modification the accelerating electrode 3 is dispensed with, the boundary electrode 6 taking its place. The control electrode 5 may be divided into two parts 5a, 5b, Fig. 5, oscillating in antiphase ; these electrodes may be cylinders or, as shown, discs connected to opposite conductors of a Lecher wire circuit 16, to one end of which output electrode 11 is also connected; in this arrangement the boundary electrodes are omitted, so that a weak velocity-modulating field extends right up to the reflectors 4, 10. The energy may be extracted from the 'faster electrons by an electrode system 17, 18, 19, Fig. 6, similar to the control system, the spent electrons being collected at low velocity by collector system 21, 22. Alternatively these electrons may be reflected back into the output system by a reflector 25, Fig. 7, and multiple reflections may also occur in this system; as shown, the control and output systems are twin cylinders 5a, 5b, 17a, 17b, oscillating in antiphase, but the disc arrangement of Fig. 5 may also be used for both systems. When used as an amplifier, the reduction of damping by the reflected electrons is adjusted to be less than that required for self-sustained oscillations, and the control signal is applied to the electron gun or to the reflecting electrode.