GB1462463A - Magnetic structure for focusing of linear beams - Google Patents

Abstract

1462463 Transit-time tubes VARIAN ASSOCIATES 10 April 1974 [13 April 1973] 15989/74 Heading H1D In a linear beam tube, e.g. a klystron or travelling-wave tube, the beam is magnetically focused by a structure providing an axial magnetic field and having a pair of apertured, axially spaced, polepieces the first of which- 18, 57, 56-is provided, around its aperture 36, with an annular region 43 of reduced magnetic permeability, providing a controlled increase of magnetic flux leakage into the gun region, to move the point of magnetic field reversal back behind the cathode 25 and thereby permit substantial coincidence of the magnetic and the electrostatic field lines between the cathode and the anode 28. The polepiece at the collector end of the tube may be similarly constructed, to permit a more uniform expansion of the beam in the collector, and to prevent the beam acquiring excessive rotational energy therein. The region 43 may be of copper, to facilitate cooling of the anode 28. As shown, the gun is provided with a beam focus electrode 31 and a multi-apertured shadow grid 33 closely adjacent the cathode surface, both at cathode potential, and a multi-apertured control grid 32, the apertures of which register with those of the shadow grid, and with concavities which form a dimpled surface of the cathode. Each polepiece is energized by an annular, radially magnetized magnet 21, the two magnets being coupled by a cylindrical yoke member 23.