Abstract: A millimeter coupled cavity travelling wave tube has each of its slow wave structures formed of at least one longitudinally extending member having holes made therethrough by a hobbing process, which holes constitute at least in part the cavities of the slow wave structure. In a preferred embodiment a one and one only such longitudinally extending member is provided, the holes therein each a whole cavity. The hobbing is such that a buttress is left outstanding from each cavity facing surface of a cavity separating wall and the beam hole is bored axially through said member from end to end through said buttresses. After machining of the cavity coupling holes in the cavity separating walls (e.g. by spark erosion) the cavities are closed by plates brazed to opposite faces of the member.

Abstract: A travelling wave tube of the kind having clover leaf cavities is provided with a periodic permanent magnetic structure, in which the magnetic material is located within noses projecting into the cavity space. A barrier between the magnetic material and the cavity space defines an evacuated envelope. Because the magnetic material is within the volume swept out by the cavity dimensions, it is positioned very close to the electron beam path.