Patent GB-841791-A (GB)
Title: Improvements in or relating to travelling-wave electron discharge devices
IPC: H01J23/27
Filed: 1958-04-25
Abstract: 841,791. Travelling-wave tubes. GENERAL ELECTRIC CO. April 25, 1958 [May 6, 1957], No. 13203/58. Class 39(1). In a travelling wave tube comprising a plurality of electron beam generators projecting electron beams through a plurality of slow wave structures connected in parallel, the slow wave structures are connected together along the lengths thereof at intervals which are sufficiently small to maintain the axial component of the wave associated with each of said structures in phase. The amplifier shown comprises a travelling-wave tube 1 having two electron guns 3 and 4 mounted in an envelope 2 which is surrounded by a focusing coil 7. Electron gun 3 comprises a cathode 8, heater 9 and an apertured accelerating electrode 10 and emits an electron beam 24 which passes through a helix 29 to a collector 5. Electron gun 4 comprises similar components 14, 15 and 16 and emits a beam 25 which passes through a helix 30 to collector 5. 'The helices 29 and 30 may be wound in the same sense or in opposite senses and are welded or brazed together at points one turn apart, and are held in position in the envelope 2 by four elongated insulating members 31 which carry conductive strips 54, e.g. of graphite, to minimize reflections. Apertured electrodes 27 and 28 serve to match input and output circuits to the helices 29 and 30, electrode 27 serving also to shape the beams 24 and 25. Electrode 27 and the input end of the helices are connected through a coaxial line 36 to a source 37 of high-frequency waves. A high-frequency choke in the form of a short-circuited quarter wave line 39 is connected across the line 36, and the outer conductor of the line is grounded by a connection 38 so that the helices 29 and 30 are maintained at D.C. ground potential. Electrode 28 and the output end of the helices are connected through a coaxial line 40 to a utilization device or load 41. Power for the heaters 9 and 15 is supplied by sources 50 and 51 respectively, and the cathodes 8 and 14 and accelerating electrodes 10 and 16 are connected by respective leads to variable tapping points on a source 43 which also supplies the collector 5, thus enabling unequal velocities or unequal currents in the beams to be used to increase the bandwidth of the tube or to permit simultaneous operation in two separate frequency ranges. Alternative slow wave structures, Figs. 3-7 (not shown), comprise four or five helices arranged in contact, or two or four helices arranged with their axes separated by a distance greater than the diameter of a helix, points along the lengths of the helices being connected together by straps or by conductive rings. Electron beams are directed axially through the helices. Fig. 8 shows a " helix-derived " structure comprising two members 81 and 82 each consisting of annular conductors 83 connected together by two series of conductive straps 84 and 85, one series of straps of one member being in contact with one series of straps of the other member. A similar structure of four members, Fig. 9 (not shown), may be built up by employing four series of connecting straps in each member. Figs. 10 and 11 show a further " helix-derived " structure comprising two groups of rods 101-106 and 107-112 stacked as shown to form one and a half turns of nine "helical" configurations, the arrangement being repeated to form " helices " of the desired length.