GB918016A - Improvements in or relating to magnetic-focusing systems for travelling wave tubes - Google Patents

Abstract

918,016. Travelling wave tubes. PHILIPS ELECTRICAL INDUSTRIES Ltd. June 24, 1959 [June 27, 1958], No. 21690/59. Class 39 (1). In a magnetic focusing system for a travelling-wave tube having a longitudinally extending delay line 28, comprising two spaced apertured polepieces 11 to each of which is attached a set of radially-extending permanent-magnet bars 12 the bars of one set being magnetized in the opposite radial direction to the bars of the other set and the polepieces being spaced apart with their axes coaxial so as to accommodate the delay line between them, soft iron members 13 connecting the outer ends of the bars, and a series of apertured high-permeability ferromagnetic discs 17 alternating with non-magnetic (e.g. hard paper) spacing discs 18 arranged coaxially between the polepieces to improve the field uniformity; there are provided adjacent each polepiece two soft-iron rings 19, 20, 21, 22 of which the ones 19, 21 nearest the polepiece have an internal diameter which is substantially equal to the maximum cross-sectional dimension of the polepiece, an axial dimension substantially equal to that of the polepiece and a radial width half the axial dimension, while the second rings 20, 22 have the same external diameter as the first rings, one half the radial width thereof and from one third to one half the axial dimension thereof, the rings 19, 20 and 21, 22 each being spaced apart a distance equal to one half the axial dimension of the second rings. The ring 19 at the gun end may have a slightly reduced outer diameter for about half its length so that its radial width is reduced by about a quarter at this point 27. Spacer members 23, 24, 25 are of hard paper, members 26, 27 are of brass.