GB864215A - Improvements in or relating to electron beam-generating assemblies - Google Patents

Abstract

864,215. Travelling wave tubes. SIEMENS & HALSKE A.G. June 25, 1959 [June 25, 1958], No. 21844/59. Class 39(1). In an electron beam generating assembly, particularly for a travelling wave tube, a beam of electrons is emitted from a cathode 1, Fig. 3, and directed towards a region of alternating or uniform magnetic field, the gun is immersed in a magnetic field and in the space between the cathode and the said region the focussing is by magnetic means 11, 12 only, so arranged that in the direction of propagation of the beam the magnetic field increases from its intensity at the cathode surface to one value, decreases and subsequently increases to a higher value in the said region. The cathode may have a concave, planar or convex emitting surface and the magnetic means comprises an axially adjustable magnetic cylindrical member 12 in screw-threaded engagement with the exterior of magnetic member 11. The beam is focussed through an aperture in member 11 on to a helical delay winding 5. The distribution of the magnetic field along the axis Z of the tube is shown in Fig. 4, the magnetic field increasing from its value BK at the cathode surface K to maxima M and V, the axial position and magnetic intensity of the field at the maximum M being simultaneously variable by displacement along the tube axis Z of the member 12.