Field enhancement in traveling wave tubes with tapered pole pieces

Abstract

In many millimeter and microwave devices, the heaviest component is the magnetic focusing structure. Therefore, a decrease in the bulk of this structure can produce a significant reduction in the mass of the entire device. In this paper, we propose a tapered pole piece designed to reduce bulk and/or enhance fields in periodic permanent-magnet focusing structures. To compare these structures with conventional designs, computer calculations have been performed by the finite-element method. The calculations show that the tapered pole piece can offer field enhancement or reduction of mass and bulk of the order of 50%. Finite-element analyses of heat conduction show a favorable comparison of the tapered pole piece with conventional structures in transporting heat away from the working space. The simplicity of form of the tapered pole-piece design, the considerable reduction of bulk it affords, and its adequate heat-handling capabilities make it a promising candidate for widespread traveling wave tube use.