MAGNETIC CIRCUIT FOR MM-WAVEBAND MAGNETRON WITH AXIAL CATHODE SUPPORT

Abstract

We report composite permanent magnet and iron pole-piece magnetic circuit for 8 mm waveband (35 GHz) non-incandescent cathode magnetrons operating in the spatial-harmonic regime. This reduces required values of magnetic induction to affordable figures and allows one to design magnetron permanent magnet magnetic circuits that have simple system assembly, reasonable mass-dimensional characteristics, and low cost impact.
We chose to assemble the outer rim (magnetized normally towards to and away from the z-axis in the left and right poles, respectively) of each pole from a number of identical segment blocks with the same external diameter of magnetic material. Total axial extent of the both pole assembly and its external diameter are varied to achieve optimal mass-dimensional characteristics; central inserts house the iron pole-pieces, which also serve as magnetic field concentrators in the work gap of magnetron. Standard distance between the left and right pole assemblies of the permanent magnet focusing systems for mm waveband magnetrons manufactured at the Vacuum Laboratory of Department of Vacuum Electronics of IRE NAS of Ukraine is 25 mm.
As the engineering criterion, we adopted the principle of the equal specific contribution into the z-component of the magnetic induction at the center of the work gap from a given portion of magnetic material. Practically, for the given magnetic induction value at the center of the work gap (which was set at 0.85 T), we calculated the total volume of magnetic material (of the both magnet poles) for possible dimensions of the magnetic circuit and chose those with minimal possible total mass.
Thus, we worked out the design of permanent-magnet magnetic circuit for millimeter wavelength range magnetrons, which ensures optimum mass-dimensional characteristics at a given value of magnetic induction necessary for their operation.
This work is supported in part by Emerging Security Challenges Division in the framework of NATO Science for Peace and Security Programme (Grant G5195)

Keywords: magnetic circuit; permanent magnet; spatial-harmonic magnetron; vacuum electron device; mm-waveband