GB1070529A - Electron gun - Google Patents

Abstract

1,070,529. Velocity-modulated tubes. SPERRY RAND CORPORATION. Aug. 4, 1964 [Aug. 12, 1963], No. 31055/64. Heading H1D. An electron gun for producing a hollow focused electron beam includes means for producing a magnetic field which, in the region of the cathode diverges from the axis, the cathode having a curvilinear emissive surface disposed either to coincide with a radially diverging field line, or tilted back, axially, with respect to the field line which cuts its radially innermost edge, whereby electrons emitted from any point of the surface possess a magnetic potential not greater than that of electrons emitted from points less remote from the axis. A focusing coil 11, Fig. 2, provides an axial field within the drift tube 25 of a klystron or travelling wave tube, and, with a bucking coil 12, a radially diverging end field in which the gun cathode 17 is mounted with its emissive surface 18 coincident with the flux lines. The gun further includes focusing electrodes 23 and 24, and an anode 20 which provides a substantial axial component of electric field. In another embodiment (Fig. 7, not shown) the emissive surface is tilted back with respect to those flux lines which pass through its front edge. In a further embodiment (Fig. 10, not shown) which includes focusing electrodes (87) and (88) and an anode (85), the cathode surface is located in a region in which the flux lines have reversed slope. The diverging magnetic field may, alternatively, be produced by permanent magnets opposed endto-end. The equations of electron flow in the beam are derived; comparison with the solid beam case is made; and the effect on the beam of various flux density distributions in the diverging field regions are discussed.