Magnetron generators with cold secondary emission cathodes, triggered by field cathodes

Abstract

As is well known, a magnetron is a generator of the microwave range. One of its most important operational characteristics is its durability. This is both a technical and economic characteristic. Therefore, increasing the service life of the device will always remain a relevant task, on a par with improving its technical characteristics. The article discusses existing designs, proposes new ones, and determines the direction of development in this area. Historically, all electron vacuum devices had a thermionic cathode. Magnetrons were no exception. However, the durability of a thermionic cathode is quite low due to its constant heating, i.e., it simply burns out. The next step was to propose the use of a secondary emission cathode (SEC) as the main cathode. Moreover, it was cold. This raised two questions. The first was the material from which to make the VEC, and the second was the need for a source of primary electrons to start secondary electron emission. The first question is still being resolved, but it is more technological in nature. The second question was initially solved simply by using the same thermionic cathode. Although the starting currents are not large, the disadvantage remained, namely the heating of the cathode. This approach increased durability by 2 to 4 times. The next step in development was the use of autoemission (field) cathodes as starting cathodes. The implementation of this approach required additional electrodes, and initially these electrodes were located in the interaction space. Along with the appearance of electrons, this approach also had disadvantages, which consisted in the unevenness of the electric and magnetic fields in the same interaction space. The next step was to move the additional electrodes outside the interaction space. This created some technological difficulties, since the geometric dimensions of the electrodes are quite small. It should be noted that in the latest proposed designs, the starting cathode is located on the VEC itself and uses the principle of superposition of electrostatic fields. In addition, such designs allow for automatic switching on/off of autoemission. This has a positive effect on the equalization of spatial charge density inhomogeneities. The use of autocathodes to start the main cathode has led to an increase in durability by 4-5 times compared to starting with a thermionic cathode. Further development in this area may be linked to the appearance of primary electrons due to the ionization of residual gases. To implement this approach, a modulator is needed to provide the necessary anode voltage pulses. Some problems associated with this approach are already apparent, although there are ways to solve them.