GB628806A - Improvements in apparatus for accelerating charged particles, especially electrons, to very high velocity - Google Patents

Abstract

628,806. Discharge apparatus. GENERAL ELECTRIC CO., Ltd., and WILLSHAW, W. E. Nov. 14, 1945, No. 30531. [Class 39 (i)] Apparatus for accelerating charged particles such as electrons or ions, comprises spaced along a stream of the particles a plurality of hollow resonators, each traversed only once by the particles and each arranged to produce when excited an oscillating electric field capable in the appropriate part of the oscillatory cycle, of accelerating particles in the stream, and means for exciting the resonators in such phase relationship that some particles of the stream are accelerated by the resonator fundamental oscillation at each of the resonators in succession. The resonators may be excited each from a separate source, or all from a single source by one or more waveguides. With a single waveguide, the length of waveguide between successive resonators may be greater than the distance between the resonators along the stream, or with cylindrical resonators whose resonant frequency is independent of their axial length, the axial length of the resonators may increase progressively along the particle stream, and the coupling points varied relative to the axial centres of the resonators. According to the Provisional Specification two waveguides, both fed from the same source and each connected to every other resonator, may be used. An electron beam may be produced from a thermionic cathode arranged within the first accelerating resonator, or by an electron gun, which may be pulse-operated in synchronism with the pulse-operated highfrequency source. The electron stream may be initially focused to counteract spreading of the beam in passage through the resonators, with or without additional focusing means, such as magnetic coils, round the stream between the resonators, or grids in the path of the stream. The successive resonators may consist of a cylindrical tube divided into separate resonators by annular partitions fixed within the tube or of a solid metal block pierced by a cylindrical hole, out of which open recesses forming the cavity resonators. The walls of the resonators may form part of the walls of a vacuum-tight enclosure, or they may be totally enclosed within an evacuated outer jacket. As shown, three cylindrical resonators 3, 4, 5 are joined by tubes 6, 7 coaxial with them. A tube 8 fixed to the resonator 3 is terminated by a glass seal 9 supporting a thermionic cathode 10. Within the tube 8 is a diaphragm 12 acting as an accelerating electrode. Flexible leads 13, 14 for the cathode and heater pass through a further glass seal 15 in the jacket 1. At the other end of the jacket a Lenard window 18 is situated opposite the outlet tube 17 from resonator 5. A rectangular waveguide 19 sealed through the jacket 1 is fixed to the lower part of each of the resonators. The end 20 of the waveguide is closed, and the end 21 emerging from the jacket is connected through a vacuum-tight joint 22 with an attenuating section 23 of waveguide, fed from a pulseoperated magnetron 24. The waveguide 19 is coupled to the resonators by loops 25, 26, 27 mounted on conical supports. The loops are spaced at half-wavelength intervals, and the loop 27 spaced from the closed end 20 by a quarter-wavelength. The resonators may be tuned by adjustment of the plugs 31, 32, 33. The apparatus of Fig. 1 may be modified, Fig. 2 (not shown), for X-ray generation, by replacing the Lenard window 18, Fig. 1, by a water-cooled target. The resonators 3, 4, 5 may be watercooled.