GB850521A - Travelling wave tube attenuator - Google Patents

Abstract

850,521. Travelling wave tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Aug. 20, 1957 [July 5, 1956], No. 20861/56. Class 39(1). In a travelling wave tube in which a loaded hollow pipe waveguide has cavities of clover leaf cross-section formed by radial inward projections, the guide is divided into two longitudinal parts each terminated by an attenuator formed of non metallic blocks of power absorbing material comprising at least part of the inward projections and located on opposite sides of a dividing metallic plate between the two parts of the guide. The guide is loaded with transverse baffles and the lossy blocks are in contact with the dividing metal plate. The heat dissipated in the lossy material can thus be conducted away to the partition which is hollow for water cooling or may be provided with an internal water jacket or coiled pipes. The delay line is preferably of clover leaf type having baffles between adjacent resonators each baffle being provided with light slots, and adjacent resonators being relatively rotated by 45 degrees while the resonators themselves are given clover leaf form by four inwardly radially projecting fingers or wedges which give the magnetic field component radial as well as circumferential components. The wedges of the mid filter section of the delay line are recessed so that lossy blocks 4 can be inserted therein and adjustably preset to obtain the desired degree of magnetic field component current interception by the loss material and by the outer guide wall. Alternatively the lossy blocks can be fixed and soldered to plate 3 and adjustment of the relative amounts of magnetic field component current interception obtained by means of adjustable stubs in the waveguide walls, e.g. ring or sleeve stubs. The lossy material may be of porous alumina ceramic impregnated with carbon. The wedges or fingers 1 may be wholly of resistive (lossy) material. The lossy blocks may be so designed and positioned as to terminate each half of the delay line in its characteristic impedance so that together with plate 3 they provide complete isolation of the output from the input. The Provisional Specification states in addition that the invention can be applied to linear accelerators.