Patent GB-548725-A (GB)
Title: Improvements in or relating to apparatus for controlling the flow of electrons in an electron stream
IPC: H01J25/24
Filed: 1940-03-19
Abstract: 548,725. Electron velocity-modulated tubes. LELAND STANFORD JUNIOR UNIVERSITY, BOARD OF TRUSTEES OF. March 19, 1940, No. 5120. Convention date, April 20, 1939. Addition to 523,712. [Classes 39 (i) and 40 (iii)] In ultra-high frequency oscillators such as described in parent Specification wherein a beam of electrons is velocity-modulated by standing waves to " bunch " the electrons into groups, a single resonator in two parts 21, 22, Fig. 2, is used the chamber between the two having a standing wave generated therein to react with the electron beam in the gaps 5, 5<1> ; the chamber within the cylinder 21 acts as the drift space. The gaps are unequal so that the voltage drop and field intensity will be unequal ; in consequence the node for the standing waves will be to one side of the chamber. The support wires 71 for the cylinder 21 are placed at this node. The indirectly heated cathode 11 is supported from insulating posts 15 and with the collinating electrode 16 directs the beam through the grids 18, 19 and 20 ; a bias potential from the battery 17 is applied to the resonator 22. The modulated beam reacts on the standing wave at the gap 51 to maintain oscillations, power being taken out by a loop 32. Some electrons pass through a hole 24 in the lower side of the resonator and are deflected by a magnet 25 into a velocity spectrum which is observable on the fluorescent screen 26. The oscillator is continuously evacuated by connection to a pump through the tube 30. A water cooling pipe 31 surrounds the resonator. In a modification wherein the resonator is enclosed in a sealed-off glass vessel 36, Fig. 4, tuning may be effected (i) by variable potential applied to an insulated cylinder 39 within the inner cylinder 37 and (ii) by an adjustable metal rod 41 within the projections 40. This arrangement acts as a superhet receiver with signals applied through the loop 32 mixing with the standing wave produced in the oscillator ; the beat frequency is detected by the two grids 45, 46 which reflect low velocity electrons but pass high velocity ones to an output 48 connected to an amplifier 49. By variation of potential on the cylinder 39 the oscillator may be turned on or off, and quench potentials may be applied to this cylinder. For large outputs an annular cathode and resonator can be used, the annulus having a cross-section similar to Fig. 2. The sides of the resonator cylinders may be curved as shown in Fig. 5, the resonators are of the quarter wave concentric line type but they may be long enough to allow for two nodes in the standing waves with support wires 56, 56<1>, Fig. 6, at each node. In a further construction electrons from a curved cathode 63, Fig. 8, pass through a hole 66 in a projection on an anode 73 ; this hole is focused by an electromagnet 69 on to the gap 51<1> which in turn is focused on a hole 74 in the end wall of the inner cylinder; the standing waves in the resonator give velocity modulations. The hole 74 may be large enough to allow the whole beam to pass through it under all conditions. Tuning may be effected (i) by movement of the inner cylinder 72 whose upper end bears on leaf springs 79 through insulation rods 78 the lower end bearing through other rods on the adjustable plate 78a and (ii) by adjustment of the lower side 81 of the outer cylinder by the nut 82 through rods 83. In another construction the resonator 88, Fig. 10, has a concentric inner cylinder 89 attached by the trunnions 90; in a modification of this form, a grid 97, Fig. 9, is supported from the resonator 95. The length of gap between the inlet grid 91 or 96 to the resonator to the grid 92 or 97 is such that the electron beam is subjected to more than one cycle of the standing wave which results in velocity modulation and bunching the reaction back to the standing waves being through a shorter period and giving thereby more effective interaction. In a further form a curved cathode 102<1>, Fig. 12, directs the electrons through a grid into a gapped cylindrical space insire a resonator 1001 supported by trunnions 107 ; this figure shows an annular construction but description is also given of a simple arrangement consisting in cross section of one side only of the resonator shown in Fig. 12. The Specification as open to inspection under Sect. 91 also describes matter forming the subject of Specification 545,146 and a construction, Fig. 16 (Cancelled, not shown), using two resonator chambers coupled by a rod projecting more in one resonator than in the other. The cathode is in the form of a grid with an oxide coating on the side facing the heater coil so that the coating is not subjected to bombardment by positive ions. This subject-matter does not appear in the Specification as accepted.