Patent GB-599253-A (GB)
Title: Improvements in or relating to electron discharge apparatus
IPC: H01J25/10
Filed: 1944-02-18
Abstract: 599,253. High-frequency discharge apparatus and generating circuits therefor. WESTERN ELECTRIC CO., Inc. Feb. 18, 1944, No. 3106. Convention date, Oct. 11, 1941. [Classes 39 (i) and 40 (v)] An electron stream controlled so as to form groups or bunches is projected through one or more elongated hollow, preferably cylindrical, electrodes 20, 21, Fig. 1, to impinge on a target 19. The hollow electrodes are connected alternately to the ends of an oscillating circuit 31, 32 ; and these electrodes and the target electrode are maintained at successively higher positive potentials relative to an earthed accelerating grid 18. The grouping means, such as space-charge control grid 17 is linked in antiphase with the first electrode 20, for example, by condenser 34 or by induction. The length of each hollow electrode is such that, at the electron velocity imparted by grid 18, the time of flight through it is one half-cycle of the oscillation. When the battery 27, resistances 28, 29, 30 and the impedance of circuit 31, 32 are adjusted to give correct operation (the conditions of self-starting and stability are discussed) the high-frequency amplitude is just equal to the potential difference between 18 and 20, which is equal to that between 21 and 19 and half that between 20 and 21. Under these conditions, as is illustrated diagrammatically in Fig. 2, each electron bunch entering the system suffers no substantial change in kinetic energy since it passes each of the gaps between the electrodes 18, 20, 21, 19 at times T1, T2, T3 when the instantaneous voltage across the gap is zero ; the energy of oscillation is derived solely from the potential energy acquired by the electrons while they are within the hollow electrodes. There may be more than two hollow electrodes connected alternately together, or only one electrode 21, Fig. 8. Instead of grid control with capacitative or inductive linkage, an electrode 20a of length twice that of electrode 21 may be used. As shown in Fig. 9 this electrode, which is biassed by battery 40 negatively relative to the accelerating grid 18 by an amount only a little less than the oscillation amplitude, only permits electrons to pass during the short period T1 at the positive peak. The group of electrons travels during one whole cycle in electrode 20a and energes at time T4 in correct phase to pass through electrode 21, without change in kinetic energy as before. Velocity modulation may be used to produce bunching provided the modulation depth is kept small to minimize differences in transit time through the conversion electrodes. To obtain the necessary increased drift time without undue length of drift space, an electrode 50, Fig. 12, at a low potential, say 50 volts positive, may be interposed in the drift space between drift tube 47 and its connected grid 51. Resonant cavity circuits 45, 41 may be used, both for velocity modulation and for conversion, the latter being split into two halves insulated at 43 to enable the successively increasing positive potentials to be applied to conversion electrodes 20, 21 ; the high-frequency potential along these electrodes is equalized by allowing a suitable amount of leakage from the resonator. Feed-back in correct phase is secured by coaxial line 48, 49. In another form, Fig. 13, velocity modulation is effected by electrode 20 itself in conjunction with grid 18 ; in this case the electrode 20 must be long to give sufficient drift time which must exceed a multiple of half-cycles by a quarter-cycle to give correct phasing.