Travelling wave tube with external permanent magnetic focussing device - has annular pole shoes of two coupled annular discs, one disc thickness corresponding to magnetic flux

摘要

The travelling wave tube has a cylindrical vacuum vessel, and the permanent magnetic focussing device is mounted on the vessel outer wall. the device consists of several permanent magnet rings, between which are fitted annular pole shoes which surround closely the vacuum vessel by their inner aperture. The pole shoes consist of two coupled annular discs, one being of greater thickness corresponding to the magnetic flux. This ring surrounds the vacuum vessel at a slight spacing. The other annular disc is of flexible sheet metal and has an inner aperture,slightly smaller than the vacuum vessel diameter. Thus the edge of the inner aperture bends in a funnel-shaped manner when inserted onto the vessel, which results in centering of the pole shoes.