Patent GB-743593-A (GB)
Title: Improvements in or relating to electron velocity modulation apparatus
Inventor: BECK ARNOLD HUGH WILLIAM
IPC: H01J25/24
Filed: 1953-02-27
Abstract: 743,593. Velocity-modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. Feb. 27, 1953, No. 5567/53. Class 39 (1). Space jump amplification is obtained in a velocity-modulated tube by changing the crosssectional area of the drift tube at suitable intervals, preferably an odd multiple of a quarter plasma wavelength, along the length thereof, so that the plasma wavelength and hence the propagation constant of the space charge waves along the drift tube is altered in such a manner that useful amplification, which may be positive or negative, is obtained. The effect may be combined with the known velocity jump amplification process by maintaining the sections of the drift tube at different D.C. potentials, and a schematic of such an arrangement is shown and discussed in a mathematical analysis which brings out the relationship between space jump and velocity jump amplification. Embodiments are also described in which space jump amplification is usefully employed without combining it with velocity jump amplification. In one such embodiment, Fig. 4, the velocity-modulated tube comprises two resonators 16 and 17 joined by a drift tube having three narrow sections 18, 19 and 20 and two wider sections 21 and 22, all combined in an integral metal structure having an extension forming an electron collector electrode 23. A thermionic cathode and focusing cylinder 24 are supported in a vitreous envelope portion 25 sealed to the resonator 16 by a cylindrical flange 26, the wall of the resonator 16 forming the anode of an electron gun, the beam from which is focused by a magnetic field indicated by the lines B. The resonators 16 and 17 are provided with respective sets of hollow cylinders 27 and 28 to form a buncher gap 29 and a catcher gap 30 and have input and output loops 31 and 32. In a further embodiment, Fig. 7, a triode electrode structure comprising an indirectly heated cathode 36, control grid 37 and electron permeable accelerating anode 38 is contained in a glass envelope portion 35 sealed to the end wall of a wide section of drift tube 39 which communicates with further alternately narrow and wide sections 40, 41 and 42. Section 42 is joined to an extension 43, such as a glass tube, containing a helix 44 and terminated by a collector electrode 45 which is provided with a heat radiator 46. The helix 44 is terminated by a probe 47 and quarter-wave sleeve 48 for transferring waves into an output wave-guide 49 provided with a matching section 50. A magnetic focusing coil 51 energized by a source 52 surrounds the amplifier tube. The anode 38, the drift tube and the collector electrode 45 are maintained at earth potential. The cathode 36 is connected through bias resistor 53 to the negative terminal of the high tension supply 54 and the grid 37 is connected to a coaxial line input circuit 58. Input signals applied to the grid 37 cause the electron beam passing through the anode 38 to be charge density modulated. The drift tube sections 40 and 41 are each a quarter plasma wavelength long, and section 42 is of such a length that the A.C. current is a maximum within the helix 44. Other types of wave-guide propagating electromagnetic waves in a slow mode may be used in place of the helix 44, and such wave-guide means may also be used at the input end. Negative space jump amplification may be used to reduce the shot noise in an electron beam prior to crossing the buncher gap of a klystron and an arrangement is described in which a space jump drift tube having two wide sections and one narrow section is located between an electron gun and the buncher resonator of a conventional klystron and is terminated by a grid. The cathode is surrounded by a shielding magnetic pole-piece which also forms the anode of the electron gun, and in conjunction with a second pole-piece surrounding the collector electrode sets up a magnetic field along the beam axis.