Patent GB-867699-A (GB)
Title: Improvements in or relating to space-charge wave tubes
IPC: H01J25/34
Filed: 1957-12-06
Abstract: 867,699. Space charge wave tubes. SIEMENS & HALSKE A. G. Dec. 6, 1957 [Dec. 7, 1956], No. 38065/57. Class 39(1). In a space charge wave amplifier or oscillator tube device, the beam is given periodic characteristics in dimension such as a ripple, Fig. 2 (not shown) or indirection e.g. a slalom or cycloidal path, Figs. 3, 4, along its length and carries a slow backward or forward space charge wave, while the unloaded hollow pipe waveguide carries a fast forward wave a spatial harmonic of the slow space charge wave interacting with the fast waveguide wave to give up energy thereto so as to operate as a forward wave amplifier or a backward wave oscillator. The spatial harmonic components utilised travel faster than the fundamental. In Fig. 2 (not shown) the gun potentials are such as to launch a rippling beam, a uniform axial magnetic field keeping the amplitude and wave length of the ripples constant along the length of the beam, or alternatively the beam ripple may be produced by an AC longitudinal magnetic field. In the modification of Fig. 3 a slalom electrostatic focusing field is produced by plates 8, 9 and rods 10, the plates 8, 9 preferably forming parts of the waveguide wall. The waveguide mode is a H 11  or H 10  mode depending on whether the waveguide is of circular or rectangular cross section (respectively). The electric component of the wave is transverse and is strongest at the Z axis so that the interaction between waveguide wave and beam space charge-wave is effectively at discrete points along the Z axis. In a modification, Fig. 4 (not shown) the electron beam follows a cycloidal path in crossed electric and magnetic fields, the electric field plates preferably forming part of the waveguide walls as in Fig. 3. The E component of the wave is longitudinal (E 01  wave for circular crosssection or E 11  wave for rectangular crosssection waveguide) interaction taking place in the large loops of the cycloids, or the E component of the wave is transverse and is coupled to the beam in the small loops of the cycloids, in which case the wave is an H 11  wave or an H 10  wave according as to whether the waveguide is of circular or rectangular cross-section respectively; in these cases the E wave component direction reverses as the electron direction reverses in the small loops thereby improving the interaction. In another modification, Fig. 5 (not shown) a forward wave amplifier has a waveguide bent at both ends and carrying an E 01  or E 11  wave according as to whether the waveguide is of circular or rectangular cross-section, and the gun potentials are such that the beam has ripples, the amplitude and wave length of the ripples being kept constant by a focusing magnet which comprises a plurality of bar magnets or a cylindrical magnet. Glass or ceramic windows soldered or alloyed in position seal the ends of the guide. In a backward wave oscillator Fig. 6 the waveguide is bent at the output end 26 adjacent the gun and has a non reflecting lossy block 30 at the collector end. The waveguide wave is 'forward' and the space charge wave backward. The gun 29 and collector 28 in Figs. 5 and 6 may be inside the guide instead of outside as shown but this increases spurious reflections.